Commands list

Commands list

[Through release 4.19. Last updated: 8-October-2004 -- by Jim Solomon]

ABS
Compute the absolute value of the pixels intenity.

ADD [NAME]
Add the image in memory to the image designated by NAME on the disk (the image must be in the current directory).

ADD2 [NAME] [NUMBER]
Adds [number] images in the sequence of images having the generic name [name].

Example

ADD2 I 3

adds the images I1.PIC, I2.PIC & I3.PIC.

Click here for an application.

ADD3 [NAME] [FWHM] [NUMBER]
When using the command REGISTER with deep-sky images, a file FWHM.LST is created on your hard drive. In this file, the first column contains an image index and the second one corresponds to the largest FWHM (along either X or Y axis, whichever is greater) of stars within the image.

Images indexes appears according to increasing FWHMs. So, it is possible to determine the best images in the series by a simple look at this file. The command ADD3 is essentially the same as ADD2, except that only the images with FWHM better that [FWHM] will be added. ADD3 uses the file FWHM to do so. Then you may add only the best images of the series.

Example: ADD3 M51- 1.9 12

ADD_MAX [NAME]
Suppose the intensity I1(x,y) of a pixel in the image I1 at coordinates (x,y) and the intensity I2(x,y) of a pixel in the image I2 at the same coordinates (x,y). ADD_MAX produce a new image, I, where the intensity of pixel (x,y) is:

I(x,y)=I1(x,y) if I2 <= I1
I(x,y)=I2(x,y) if I2 > I1

In other word, a pixel of image I1 is replaced by a pixel of image I2 if the local intensity of I2 is superior to I1.

The usage of ADD_MAX is simple:

LOAD I1 (load in-memory the I1 image) ADD_MAX I2 (compute substitution)SAVE I (save the result)

ADD_MAX is compatible with 16-bits format (gray level images) and 48-bits format (true-color images).

Click here for a typical application.

ADD_MAX2 [NAME] [NUMBER]
Function very similar to ADD_MAX but process many images simultaneously. For example for stack images I1, I2, I3, I4, I5, enter the command:

ADD_MAX2 I 5

This function is very efficient for construct long exposure star-trails images. About this method read the excellent paper of Peter Michaud (Gemini observatory) in the Marsh 2004 issue of Sky and Telescope. Click here for an example.

ADD_MEAN [NAME] [NUMBER]
Calculate the average of a sequence of images.

ADD_NORM [NAME] [NUMBER]
Same command as ADD2 but normalise intensity to 32700 if value of one or many pixels are upper to 32768 after coading.

ADD_NORM2 [NAME] [NUMBER]
Same command that ADD_NORM (addition of a sequence of images and normalize the most intense pixel to 32767 if necessary), but the zone where normalize is computed is selected with the mouse. This gives flexibility for some situation cases to avoid saturating a specified part of the image.

AF3 [COEF]
Adaptive filtering of the noise in an image. Adaptive filtering consists of adjusting the strength of the filter as a function of local statistical criteria. The filter will be most active where the signal to noise ratio is low. This type of filter reduces the noise while conserving a maximum of details in the image.

The parameter [coef] contains a value that fixes the global strength of the filter. The filter does not act if [coef]=0, and the filter gets stronger as the value of [coef] increases. Typically, [coef] is between 0.1 and 5.

AF3 uses a zone of 3x3 pixels, centered on the pixel being processed, for the statistical calculation.

See also EXPORTASC.

Example: IMPORT_ASC FILE

IMPORT_ASC2 [NAME] [SIZE X] [SIZE Y]
Load an image stored in an ASCII file in the simple form of a single column of real numbers. The length of this vector must be equal to [SIZE X] x [SIZE Y]. See also command IMPORT_ASC.

INFO
Returns information about current image (size, date/time of exposure, integration time). For a FITS file the command return also principal keyword of the header.

INSERT [IN1] [IN2] [MASK] [VALUE]
For a given pixel of coordinate (x,y) in the [IN1], [IN2] and [MASK] images, if the intensity in the [MASK] image is equal to [VALUE] then the in-memory intensity image pixel is [IN2], else the intensity is [IN1].

Example:
LOAD M51
OFFSET -500
CLIPMIN 0 0
SAVE MASK
INSERT MASK M51 MASK 0

JD2DATE [JULIAN DAY]
Convert Julian day to date.

JPG2PIC [IN] [OUT] [NUMBER]
Convert a sequence of JPEG file to PIC or FITS sequence (the final format is dependant of the choice in the setup dialog box of File menu).

Consider the input sequence IM1.JPG, IM2.JPG and IM3.JPG. To convert to image R1.PIC, R2.PIC and R3.PIC (or R1.FIT, R2.FIT and R3.FIT), enter the command:

JPG2PIC IM R 3

L_ADD [LINE1] [LINE2]
Computes for each row of the current image the add of lines between [line1] and [line2]. The sum is maximized to 32767. The "L_" commands (line commands) are adapted for spectra processing. Click here for details.

The result is represented as a new image with the same width as the input image and 20 identical lines in height. Each pixel corresponds to the mean of the input lines in the current row.

L_ADD2 [LINE1] [LINE2] [SKY BACKGROUND] [GAIN] [READOUT NOISE]
Same as L_ADD but by taking into account the noise for the calculation of a weight function. SKY BACKGROUND is the present sky level in ADU (Analog Digital Unit). GAIN is the camera gain (i.e 2 electrons/ADU). READOUT NOISE is the noise of camera in electrons (i.e. 18 electrons).

L_BIN
Carry out an operation of binning along vertical axis on a spectrum whose dispersion axis is horizontal. The addition zone along the vertical axis is such as with final the result of the addition contains 93% of the information of the real spectrum. Iris calculates the optimal addition width zone for reduce noise in the result. The max intensity in the binned image is normalized to 32766. The result is an image of the spectral profile where this one is to duplicate 20 times along the vertical axis. Before run the command you must frame the spectrum of a rectangle to be traced with the mouse.

For an introduction tutorial to spectrography, click here.

L_BIN2
Same function that L_BIN, but the normalization is carried out starting from the most intense pixel which is in the selection zone and not over the entire length of the spectrum.

L_CORREL [NAME]
Compute the shift in pixel unit along the x-axis of the in-memory spectrum and the [name] file spectrum. Before running L_CORREL define with the mouse a rectangle for the cross-correlation computation.

L_COUNT
Compute the mean level of a 2D spectrum (in ADU or Analog/Digital Unit). The concerned part is selected with mouse.

L_CURVE [LINE1] [LINE2] [RADIUS]
Same as L_ADD but the binning is made along a curved spectrum. The radius of curvature of the spectrum is [RADIUS]. Click here for details.

L_CURVE_TEST [LINE1] [LINE2] [RADIUS]
Draw line along the spectrum to test parameters of L_CURVE command.

L_DIV [NAME] [COEF]
Same principle as L_SUB with a division with the line and a [coef] coefficient.

L_EXPAND [HEIGHT]
Creates a new image with [height] identical lines equal to the line obtained with, L_MEDIAN, or L_ADD.

L_GAUSS [SIGMA]
Convolution of a vector image by a gaussian function. The sigma of the gauss function is given in parameter. For a typical application click here.

L_MEDIAN [LINE1] [LINE2]
Same command as L_ADD except that a median is applied instead of a mean.

L_MEDIAN_CURVE [LINE1] [LINE2] [RADIUS]
Useful for spectra processing. Same command as L_MEDIAN but along a curved spectrum. The radius of curvateur in pixels is [RADIUS].
See exemples here.

L_MERGE [FILE #1] [FILE #2] [X1] [X2]
Merge two spectra [FILE #1] and [FILE #2]. The point of at the coordinate [X1] (pixels unit) into the spectrum #1 correspond to the point [X2] into the spectrum #2. The intensity are normalized at around this point. Click here for an example.

L_MERGE2 [FILE #1] [FILE #2] [X1] [X2]
Same as L_MERGE. The only difference: the spectra are not normalized at the common point.

L_NOISE
Compute the mean level and the RMS noise of a 1D spectrum - The wavelength limits of the computation are selected with the mouse.

L_OPT
An easy to use optimal extraction function of the 1D spectrum from the 2D spectrum. See L_OPTBIN.

L_OPTBIN [LINE1] [LINE2] [GAIN (e/ADU)] [RON (e-)] [MEAN SKY LEVEL (ADU)] [KAPPA]
Optimal extraction for CCD spectroscopy. Click here for a description.

L_OPTBIN2 [LINE1] [LINE2] [GAIN (e/ADU)] [RON (e-)] [MEAN SKY LEVEL (ADU)] [KAPPA]
Optimal extraction for CCD spectroscopy. Click here for a description.

L_ORI
Return the orientation of a spectrum relative to the horizontal axis. Draw first a rectangle in the current image with the mouse around the spectra.

L_PLOT [HEIGHT]
Creates a new image with a plot of the line obtained with L_MEDIAN, or L_ADD. The width of the plot is the line width, and its height is [height]. This command produce also the ASCII file PLOT.LST.

L_POS [FLAG] [WIDTH]
Compute the position of a spectral line. If FLAG=0 the line is in absorption. If FLAG=1, the line is in emission. WIDTH is the typical width of the line(FWHM). Select un area around the line with the mouse then execute L_POS.

L_POS2
Precise evaluation of the position of a spectral in a 1D spectrum. The line influence zone is selected with the mouse. The command return the position in pixel and also the FWHM of the line.

L_REGISTER [IN] [OUT] [FLAG] [WIDTH] [NUMBER]
Register a sequence of NUMBER spectral images with the aim of a spectral line. If FLAG=0 the line is in absorption. If FLAG=1, the line is in emission. WIDTH is the typical width of the line(FWHM). Select un area around the line with the mouse then execute L_REGISTER.

L_SINC [FACTOR]
Scale a spectral image by the coefficient [FACTOR]. This function use the sinc intrepollation. For an application example click here.

L_SKY [LINE1] [LINE2] [LINE3] [LINE4]
Computes the median value for each row of the current image between [LINE1] and [LINE2]. This give the value V1. Computes the median value for each row of the current image between [LINE3] and [LINE4]. This give the value V2. The value (V1+V2)/2 is computed and substracted to each row of the current image. L_SKY is useful to correct gradient background for spectral image. In the normal situation the area between [LINE1] and [LINE2] is upper the spectrum and the area between [LINE3] and [LINE4] is in the opposite side relative to the spectrum.

L_SKY2
Command allowing to estimate the level of the sky background on both sides of a spectrum. The sky background is modelled by calculating for each columns of the images taken independently the median value of the intensities of the pixels in two zones that one definite interactively. The operator define these two zones by 4 clicks of the mouse as shows it the following image:

The click order of the points is not critical. L_SKY2 then substrat from all the columns the average of the two median intensities calculated in each one of them. The effect is to bring the level of the sky background to zero. It is an essential operation before being able to extract the spectral profile from a spectral image because it fixes the origin of the scale of the intensities. Click here for an illustration.

L_SKY3
Command, very similar to L_SKY2, allowing to estimate the level of the sky background on both sides of a spectrum. The sky background is modelled by fitting linear lines distinct for each columns from the image. The pixels of the image which are used to calculate these fit are in two zones on both sides spectrum that the operator define by 4 clicks of the mouse as shows it the following image:

L_SKY_CURVE [LINE1] [LINE2] [LINE3] [LINE4] [RADIUS]
Same as L_SKY but along a curved spectrum. Click here for exemple of use.

L_SUB [NAME]
Subtracts from each line of the current image the line in the [name] image obtained with L_MEDIAN, or L_ADD.

LAPLACIAN
Calculate the Laplacian of the image in memory.

LOAD [NAME]
Load an image in memory from the current directory (defined in the item Current Directory from the Settings tab – File menu). You can also indicate in which directory to load a particular image by specifying the full path of the image. For instance: LOAD c:\nuit7\m51.

LOADBMP [NAME]
Load a 8-bits BMP file in memory from the current directory.

LOADBMP24 [NAME] [R] [G] [B]
Load a 24-bits BMP file from the current directory and copy the RGB planes in the images [r], [g], [b] respectively.

LOADBMP24BW [NAME]
Load a 24-bits BMP file from the current directory in memory and convert the RGB planes into a B&W images.

LOADCAM [NAME]
Converted RAW file coming from a digital camera into a color image which is displayed (see also Load... command of the File menu).

Example: LOADCAM CRW_0347

LOADCFA [NAME]
Display a CFA image extracted from a RAW file (CFA = matrix of coloured filters covering the pixels of the electronic sensor).

LOADRAW [NAME] [R] [G] [B]
Converted a RAW in three files containing the primary layers of colors. For example:

LOADRAW CRW_0347 R G B TR R G B

LOADSB [NAME]
Loads an image in CCD SBIG (ST4, ST4X, ST6, ST7, ST8...) format into memory. This command also accepts compressed format.

Example: LOADSB M51

LOADSX [NAME]
Load into memory an unsigned 16-bits image (dynamic range between 0 and 65535). The level of the pixels is multiplied by 0.5 to bring final dynamics between 0 and 32767. See also: CONVERTSX, SIGNED.

LOADSX2 [NAME]
Load into memory an unsigned 16-bits image. The level of the pixels is not modified, but the images is truncated for intensities higher than 32767.

LOADSX3 [NAME]
Load into memory an unsigned 16-bits image. Value 32767 is subtracted from the intensity of all the pixels. The final level lies between -32768 and 32767.

LOADTIFF [NAME]
Load a 8-bits uncompressed TIFF file in memory from the current directory.

LOADTIFF24 [NAME] [R] [G] [B]
Load a 24-bits uncompressed TIFF file from the current directory and copy the RGB planes in the images [R], [G], [B] respectively.

LOADTIFF24BW [NAME]
Load a 24-bits uncompressed TIFF file from the current directory in memory and convert the RGB planes into a B&W image.

LOG [NORM]
Calculates the base 10 logarithm of an image where [norm] is a coefficient which adjusts the maximum dynamics of the output image and Max(imput image) is the intensity of the brightest pixel in the input image.

The logarithm of an image is used to display the range of intensity levels in one visualization. Often, during deep sky image processing, the OFFSET command is used first to bring the sky background close to level 0. The depiction of faint details is then greatly improved.

Let's calculate the logarithm of the image M51.FIT, whose sky background level is around 130:

LOAD M51
OFFSET –100
LOG 1000
VISU 1000 400

With the STAT command, you can verify that there are no pixels with intensities over 1000 in the final image.

The LOG command allows you to transform the linear intensity scale into a magnitude scale, to within a constant. This can be very useful in photometry or in various kinds of image representation (for example isophotes vizualisation).

LRGB [IN_R] [IN_G] [IN_B] [IN_L] [OUT_R] [OUT_G] [OUT_B]
Give tri-color images IN_R, IN_G & IN_B, the program compute the RGB to HSI conversion, then replace the I image by the IN_L image (luminance image). Finaly, the program perform the HSI to RGB conversion for producing the output images OUT_R, OUT_G & OUT_B.

See also: RGB2HSI, HSI2RGB, RGB2PCA, PCA2RGB, TRICHRO.

MAX [PIXEL NUMBER]
Draw a rectangle in the current image with the mouse before running that command. This will replace the [pixel number] brightest pixels of the rectangle by the median value of the remaining pixels (the median value is computed at each iteration).

This command is good for interactively removing cosmetic artefacts in an image, such as warm pixels. To remove a single pixel you will type MAX 1. But you may also remove several pixels at a time, and even remove a star (e.g. MAX 30).

MEDIAN3 [COEF]
Performs median filtering on the current image. The median value of the intensities of the pixels in a 3x3 matrix around a pixel is calculated for each pixel in the image. The corresponding point in the output image is set to this median value.

[coef] is a parameter that adjusts the strength of the filter (the action of the filter is maximum if [par]=0). If we number from n=1 to 9 the values of a 3x3 matrix sorted on increasing order, if I(n) represents the intensity of the points in the matrix and if I0 represents the intensity of the point at the center of the 3x3 matrix, MEDIAN3 performs as follows:

- if the absolute value of (I0 - I(5)) is greater than: [coef]. . (I(8)-I(2)) then the corresponding pixel I0 in the output image will be given the median value I(5);

- otherwise, the pixel I0 of the output image will keep the value of I0 from the input image.

Median filtering is an excellent tool for eliminating impulse noise in an image (cosmic rays, interference in one or two pixels, etc.). The original version of the median filter is very energetic. Used without finesse, this filter may suppress useful information (faint stars) and give an artificial texture to the filtered image. This is why a weighting factor has been added to the Iris implementation of the median filter. For images that are not too noisy, the parameter [coef] is typically between 0.80 and 0.99:

MEDIAN5 [COEF]
Same comand as MEDIAN3 but with a 5x5 matrix.

MEDIANF [SIZE] [COEF]
Carry out same work as MEDIAN3 or MEDIAN5 but by using a kernel (zone in which the median is calculated) of adjustable [SIZE]. Size must be imperatively an odd value. For example MEDIANF 9 0.8. This command is practical to erase the details of relatively large size.

MEM [#ITER]
Deconvolution using a Maximum Entropy Method. The process is iterative and contains [#iter] iterations. The size of the image must be square and equal to a power of 2 (see WINDOW3 and PADDING commands). Before running the command, select an isolated star with the mouse. It has to have a good signal to noise ratio, but not too bright, in order to avoid saturation.

Generally, 15 to 20 iterations are recommended. Try also to have a sky background close to zero (use the OFFSET command) but strictly positive.

MIN [PIXEL NUMBER]
Same command as MAX, but applies on pixels having a level lower than the median level of the area (e.g. for removing non active pixels).

MIRRORX
Rotate the image around a vertical axis.

MIRRORY
Rotates the image around an horizontal axis.

MIRRORXY
Invert the X and Y axis.

MIRRORXY2 [IN] [OUT] [NUMBER]
Permutation of axes X and Y for a sequence of images.

LOAD M51

With the mouse, define a rectangle about 30 to 40 pixels in width, avoiding the galaxy and stars. then run the STAT command (contextual menu). Iris returns a standard deviation around 8 (it is the estimation of the sky background). Then type:

MMSE 8.0

The MMSE command allows reduction of noise in the image while preserving fine detail.

MMSE [SIGMA]
Filters adaptatively noise by using the "Minimum Mean-Square Error" method. The [SIGMA] parameter contains the typical value of noise in the sky background. This value may be obtained for example with the STAT command. For example, load the M51.PIC image.

MODULO [VALUE]
Computes for each pixel the value modulo [VALUE]. The result is the current image in memory. This command allows to produce some isophote effects that may be useful to visualize images with large dynamic ranges. Select the false color palette to a better rendering.

MOSA [NAME] [DX] [DY] [TYPE]
MOSA allows you to include a set of elementary images in one image. The images are merged two at a time. The first image is in memory. The second image is designed by the parameter [NAME].

The shift between two points on the images you want to merge is contained in the variables ([DX],[DY]).

When the two images have points that overlap (which is not required), the value contained in the variable [type] allows you to choose the state of the overlapping zone in the final image:

If [TYPE] = 0: the second input image (the name in IN2) overwrites the first input image ( the name in IN1) unless the pixels in the second input image have the intensity zero. In this case, the values from the first input image are used.
If [TYPE] = 1: the first input image overwrites the second input image unless the pixels in the first input image have zero intensity, in which case the values from the second input image are used.
If [TYPE] = 2: the pixels in the output image take the maximum value of the pixels from the two input images.
If [TYPE] = 3: the pixels in the output image take the minimum value of the pixels from the two input images.
If [TYPE] = 4: the pixels in the output image take the average value of the pixels from the two input images.
If [TYPE] = 5: a bilinear interpolation is performed on the common parts of the two input images.

The format of the input images can be different.

The MOSA command is used primarily to put together several shots of the same object in order to have a single image of this object. Click here for an example.

MULT [COEF]
Multiply all the current image pixels by the constant COEF.

MULT2 [IN] [OUT] [COEF] [NUMBER]
Multiplies all the pixels of a sequence of images by [COEF]. The generic name of the [NUMBER] input images is [IN], whereas the generic name of the output images is [OUT].

Example: MULT2 I J 0.5 7

NEW [X] [Y]
Creates a new image filled with zeros. The image has a size of [X] x [Y].

NGAIN [NORM]
Normalizes the median level of an image to [norm] by multiplying the image by a constant value. This command is generally used to change the median level of a flat-field image, in order to prepare a median sum.

NGAIN2 [IN] [OUT] [NORM] [NUMBER]
Normalizes the median level of a sequence of [number] images having a generic name [in] to [norm] by multiplying each image with a constant value. The generic name of the output images is [out].

NGAIN3 [IN] [OUT] [NORM] [NUMBER]
Normalization of a sequence of images. For the difference of NGAIN2 it is necessary to define with the mouse the zone of the image in which the calculation is carried out.

NOFFSET [NORM]
Normalizes the median level of an image to [norm] by adding a constant value to the image.

NOFFSET2 [IN] [OUT] [NORM] [NUMBER]
Normalizes the median level of a sequence of [NUMBER] images of generic name [IN] to [NORM] by adding a constant value to each image. The generic name of the output images is [OUT].

NOFFSET3 [IN] [OUT] [NORM] [NUMBER]
Normalizes the median background level of a series of [NUMBER] images having the generic name [IN] to [NORM]. The generic name of the output images is [OUT]. You have to select the area in which the background level will be estimated before running the command. Use the mouse for that. This command is very useful to normalize background levels in a series of planetary images. For example, the PREGISTER command works best when the background level is close to zero, and when the image background is uniform including near the image edges (windowing is often necessary to avoid edge effects). So, a typical sequence to register a series of planetary images will be for example:

`WINDOW2 JUP I 5 5 170 170 9`	(in order to supress bad border)
`NOFFSET3 I J 0 9`	(in order to make zero level background around the planet)
`PREGISTER J K 256 9`	(in order to register the images)
`MULT3 K K .3 9`	(in order to avoid integer overflow when adding the images)
`ADD2 K 9`	(in order to composite the 9 images)

NUMBER [GENERIC NAME]
Return the number of images of an image sequence. For example, if the sequence is M31_1.FIT, M31_2.FIT and M31_3.FIT, NUMBER M31_ return 3.

OFFSET [VALUE]
Adds the constant [value] to the current image. The constant can have a negative value.

OFFSET2 [IN] [OUT] [OFFSET] [NUMBER]
Adds the value [offset] to [number] images having the generic name [in]. The parameter [out] contains the generic name of the output images.

OPT [DARK FRAME NAME]
In long exposure CCD imagery, one of the major difficulties posed during preprocessing is the dark current correction. This interference signal, due to thermal charges, is added to the signal produced by the observed objects. The problem is to suppress this interfering component of the image because it is noise that impairs the detectability.

A classic solution is to take an exposure of the object under study with an integration time T, then to take another exposure of length T while placing the detector in total darkness. This last exposure is called the dark current map. This map is a constant, to within a coefficient, for a given CCD. To first order, the coefficient is proportional to the temperature of the CCD and to the integration time. In the preceding procedure, the dark current map is simply subtracted from the image of the object.

This is, however, far from the ideal solution. In fact, this procedure implies that a dark current map must be taken after each image of the object. This is very constraining when the exposure time is several minutes or more.

Things seem to go better if the temperature of the CCD is perfectly stable. In this case, a priori only one map is necessary. It can be taken, for example, at the beginning of the observing session, and can be used to correct all the images. If the exposure time is not the same on the dark map and the image to be processed, the dark map must be multiplied by a coefficient before the subtraction. The coefficient is the ratio of the exposure time of the image to the exposure time of the dark map.

Besides the fact that is a delicate matter to maintain the detector at a fixed temperature, this method has the following inconvenience - the dark map has its own noise (readout noise) and when the map is subtracted from the images, this noise is actually added to the images.

There is a more efficient method:

- Take several (5 to 10) dark images with integration times that are not necessarily equal, but long enough to be sensitive to the dark current (they should have the same duration as the observation exposures). The CCD should be cooled to reduce the readout noise as much as possible.

- For each exposure in darkness, another one with a minimal integration time is taken. This provides the offset map.

- For each of the dark images, subtract the corresponding offset map. The resulting images then contain only the thermal component of the signal.

-Sum all the images from the previous step to obtain the dark map. This adds the thermal contributions from each image, but averages the readout noise. This map can be considered constant for a given CCD (it is still good to redo this procedure every 1 or 2 months to allow for any possible change in the electronic characteristics of the detector).

- Now a given image must be corrected. The difficulty is in finding a multiplicative coefficient, to apply to the dark map, which will optimally correct this image. This is what the command OPT does.

Iris solves this problem nearly instantaneously using an analytical approach.

You have to select an area typically 30 to 100 pixels in width with the mouse. Then run the command. [dark frame name] is the name of the dark current map. The program will return the coefficient to apply to the dark current map to create a new map that is optimal for the image to process.

Example: OPT DARK calculates the optimal coefficient for the dark map DARK.PIC to correct the current image.

The OPT command should be systematically used to preprocess deep sky images. With this command in hand, you do not need to worry about taking dark images during the night. The result is quite good because the criteria chosen minimize the noise.

OPT2 [IN] [DARK] [OUT] [NUMBER]
Same command as OPT but applies on a sequence of [NUMBER] images having the generic name [IN]. [OUT] is the generic name of the output images.

OPT3 [IN] [DARK] [OUT] [NUMBER]
Same command as OPT2 the with a more fully procedure (it is not necessary to select a zone in the image).

OPT_SUB [NAME]
Convolution of the image in memory by a kernel calculated by the command so that the PSF of stars are most similar to the image [name]. The kernel is saved at ends under the name @k.

PADDING [LX] [LY]
Sets the size of the current image to [lx], [ly]. If the image is larger than ([lx], [ly]), it is truncated. If the image is smaller than ([lx], [ly]), it is completed by pixels of zero intensity.

This command is generally useful for comparing images taking with differents CCD or before using commands that perform Fast Fourier Transforms for which the image must have a size equal to a power of 2. For example, the command:

PADDING 256 256

guarantees that the image in memory has a size of 256x256 pixels.

PADDING2 [IN] [OUT] [LX] [LY] [NUMBER]
Same function that PADDING, but applying to a sequence of images.

PCA2RGB [C1] [C2] [C3] [R] [G] [B]
The PCIA2RGB command performs the reverse transformation of the RGB2PCA command, that is, it goes from the space of the principal components to the space of the fundamental colors (R,G,B). To do this, this function needs the file containing the matrix of the eigenvectors of the covariance matrix of the three initial trichromatic images (pci.lst). For more information on this technique, see the RGB2PCA command.

PHOT [RADIUS1] [RADIUS2] [RADIUS3] [OPTION]
Computes aperture photometry. After running the command, one or several circles appear in the field. By centering the circles on the stars and then clicking on the left button of the mouse the program returns information about the star intensity.

If [option]=1, a simple circle appears.The returned information is the sum of the intensitites of the pixels inside the circle (i.e. the sum of the star intensity and the sky background).

If [option]=2, two circles appear. The signal of the star plus the sky background is integrated in the inner circle. In the area between the two circles, the mean sky background is measured. PHOT then returns the signal of the star alone (sum of the intensities I, and instrumental magnitude M). The inner circle radius is [radius1], and the outer circle radius is [radius2].

If [option]=3, three circles appear. The most outer circle radius is [radius3]. It is the same method as previously, except that the backgroung level is calculated from the area between circles 2 & 3. This allows sometimes to avoid close stars to the measured star, that may bias the measure of the sky background.

To exit the PHOT mode, execute the commande PHOTOFF.

Examples:

PHOT 6 0 0 1
PHOT 6 11 18 3

Note: it is important that a rather large number of pixels are used to determine the sky background. Moreover, as far as the inner circle is concerned, it has to be large enough to contain the whole star, but not too big in order to minimize noise level.

See application here.

PHOTM [RADIUS1] [RADIUS2] [RADIUS3] [OPTION]
This command is close to the PHOT command. The difference is that a median is used to compute the sky background level instead of a simple average. It may be useful to minimize the effect of feeble stars in the measure annulus. To exit the PHOT mode, execute the commande PHOTOFF.

PIC_ANIM [INPUT] [OUTPUT]
Function very close to DATA_ANIM. The latter calculates interpolations starting from data curves, in particular of spectra (click here for an example). PIC_ANIM applies to 2-D images to improve fluidity of the animation of a sequences. For that of the intermediate images are calculated by simple linear interpolation starting from the acquired images.

The parameter [INPUT] indicate the name of a text file which respectively contains on two columns the name of the acquired images and date of acquisition of these images (or all other identifying function of time, as for example an index value which goes into increasing).

The parameter [OUTPUT] indicate the name of a text filwhich respectively contains on two columns the name of the interpolated images and dates for which the interpolation is calculated (or an identifier function of time, in conformity with that used in the input file).

Suppose 5 images to be interpolated with the names MET1, MET2, MET3, MET4 and MET5. We create in the working directory a text file of name IN.LST containing (use a text editor for that):

met1 1 met2 2 met3 3 met4 4 met5 5

We create the output file OUT.LST:

r1 1.00 r2 1.25 r3 1.50 r4 1.75 r5 2.00 r6 2.25 r7 2.5 r8 2.75 r9 3.00 r10 3.25 r11 3.50 r12 3.75 r13 4.00 r14 4.25 r15 4.50 r16 4.75 r17 5.00 r18 4.50 r19 4.75 r20 5.00 r21 4.50 r16 4.75 r17 5.00

The images R1 and R5 for example will be identical to images MET1 and MET2 (correspondence of the dates). But moreover, between the two images observed, command PIC_ANIM will generate the intermediate images R2, R3 and R4, and so on for the whole of the sequence.

Note: file OUT.LST can be creates automatically with the assistance of command GEN_OUT, which is quite practical for long sequences. In the example one will make:

GEN_OUT OUT R 1 5 0.25

After having saved the file IN.LST and OUT.LST, we produce the interpolated sequence:

PIC_ANIM IN OUT

The sequence R1 ... R17 synthesized can be visualized with the Animation... command from Visualisation menu. You can also save the sequence in the form of BMP images for produce an animated GIF or a AVI film for example with the assistance of an adequate software:

PIC2BMP R RR 17

You have now on the disc a sequence RR1.BMP..., RR17.BMP.

PIC2BMP [INPUT] [OUTPUT] [NUMBER]
Convert of a sequence of FITS or PIC images to a sequence of 8-bits BMP images.

PIC2DATA [DATA FILE NAME]
Convert the values of the first line of the image in memory into a text file of name [DATA FILE NAME]. This command is particularly useful for the analysis of the spectral data starting from a spreadsheet or a program of display of curves.

And also an improved version of the command NUMBER. Suppose the sequence M57-1, M57-2, M57-3. The command NUMBER M57- return the number of images in the sequence (3) but mid-date of the acquisition.

PIC2FITS [IN] [OUT] [NUMBER]
Convert a sequence of PIC image into FITS a sequence. Parameters:

[IN] is the generic name of the input sequence.
[OUT] is the generic name of the output sequence.
[NUMBER] is the number of images in the sequence.

PLOT2 [DATA] [DIM X] [DIM Y] [YMIN] [YMAX] [TITLE]
Even function that ANIM_PLOT but applying to only one data file [DATA].

POINTON
This command permits selection of any points on a sky background. The list of points will then be used by commands such as POLY and SYNTHE in order to produce synthetical sky backgrounds.

Each time you click with the mouse, a small cross appears in the image, a counter increments and the pixel coordinates and intensities are stored in memory. The maximum number of points is 5000.

To come back to normal cursor mode type: POINTOFF. For an example click here.

See also: POLY, SYNTHE.

POINTOFF
See POINTON.

POLAR [0°] [60°] [120°] [DEGREE] [ANGLE] [SCALE]
Computes the polarization angle and level from 3 images obtained through a polarizing filter at angles of 0°, 60° & 120°. The three parameters [0°], [60°], and [120°] contain the names of the three corresponding images. The two resultant images contain the linear polarization level (named with the [degree] parameter), and the polarization angle (named with the [angle] parameter), respectively. The parameter [scale] allows to normalize the levels in the degree of polarization image. If [scale]=100, the image will contain the polarization degree in percents. The intensities in the polarization angle image corresponds to degrees of polarization (between 0° and 180°). The angle origin correspond to the filter with the 0° orientation. Angles are oriented counter-clockwise.

Example: POLAR P0 P60 P120 POL ANGLE 100
Click here for examples. See also POLAR_CARTO command.

POLAR2 [0°] [45°] [90°] [135°] [DEGREE] [ANGLE] [SCALE]
Computes the polarization angle and degree from 4 images obtained through a polarizing filter at angles of 0°, 45°, 90°& 135°. The four parameters [0°], [45°], [90°] and [135°] contain the names of the four corresponding images. The results consists in an image containing the polarization level (named with the [degree] parameter), and an image containing the polarization angle (named with the [angle] parameter). The parameter [scale] allows to normalize the levels in the polarization degree image. If [scale]=100, the image will contain the polarization degree in percents. The intensities in the polarization angle image corresponds to degrees of polarization (between 0° and 180°).

For an application, we are going to process a set of four images of the moon taken through a polarizing filter with four position angles 45° apart. This filter was placed just in front of a CCD detector. The exposure times are identical for the four images, which are called MP1.PIC, MP2.PIC, MP3.PIC, and MP4.PIC. The offset signal has been subtracted from each of these images (see the SUB command) and they have been carefully centered to within a fraction of a pixel with respect to each other. Then:

POLAR2 MP1 MP2 MP3 MP4 P A 100
LOAD P
VISU 5 0

The intensity levels in P.PIC express the polarization degree. For the moon the degree is often small as 5%. Comparing the polarization map and the albedo image is instructive. For the most part, the polarization rate is higher in the continental zones than in the seas. Nevertheless, there are some notable local exceptions. You will also note that some craters have a particularly high polarization rate. Click here for an example.

This type of polarization map provides information about the roughness of the lunar surface. The interpretation of this kind of document requires prudence (for example, the polarization rate at a given point on the moon is strongly dependant on the elevation of the sun at the point, and on the mineralogical makeup of the ground).

POLAR3 [0°] [45°] [90°] [DEGREE] [ANGLE] [SCALE]
Same as POLAR2 but for only three angles : 0°, 45° and 90° of the polaroid analyzer.

POLAR_CARTO [DEGREE] [ANGLE] [STEP] [SCALE]
The POLAR_CARTO command creates a polarization map from an image containing the polarization magnitude and an image containing the polarization angle (in degrees). The output image is formed of small vectors whose length is proportional to the polarization degree and whose orientation is equal to the polarization angle. An angle of 0° corresponds to a vertical vector. The center of the vector is at the point where the calculation was done.

[MAGNITUDE] is the polarization magnitude image name and [ANGLE] is the angle image name. The calculation of the vectors is performed at the intersection of a mesh whose stepsize, in pixels, is contained in the parameter [STEP]. Note that the displayed result is the average of the polarization degree and the polarization angles calculated on a zone of dimension [STEP] centered on the point.

The parameter [SCALE] adjusts the length of the vectors as a function of the polarization rate. It is expressed in pixels per percent of polarization (if the polarization rate is itself in percent).

Example: POLAR_CARTO POL ANGLE 10 30 , draws a polarization map from the images POL and ANGLE. The calculation stepsize is 10 pixels, and each segment has a length of 30 pixels per polarization percentage (this requires that a polarization rate of 100% is equivalent to level 100 in the image POL.PIC).

POLY [ORDER]
In many cases it is very important that the level of the sky background becomes as uniform as possible, and with a given value (for low flux detection, photometry,...). If the background is not uniform enough after preprocessing to perform such analyses, a solution may be to synthetize a background using mathematical functions that fits the real background. The synthetic background will be then subtracted from the original image.

POLY calculates the coefficients of a polynomial by the method of least squares from data obtained by making pointings in the image background (see the command POINTON).

The parameter [ORDER] contains the order of the polynomial to calculate. The order can range from 0 to 5. For a fifth degree, the polynomial has the form:

V = CONSTANT +C1.X + C2.Y + C3.X.Y + C4.X2 +C5.Y2 +C6.X2.Y + C7.X.Y2 +C8.X3 +C9.Y3 + C10.X4 + C11.Y4 + C12.X5 +C13.Y5

When a lesser order polynomial is calculated, only the related coefficients are included (the others are set to zero). For example, for a second degree polynomial, only the coefficients from C1 to C5, as well as the constant, are significant.

Click here for an example.

See also: SYNTHE, SUBSKY, POINTON, POINTOFF

POWER [VALUE]
Rise the intensity of the pixels of the current image to the power. The value of the power is provided by the user ([value]).

PR [INPUT] [DARK + OFFSET] [FLAT] [OUTPUT] [NUMBER]
The PR command (PR=PreProcessing) is an important command for the preprocessing of a sequence of [NUMBER] images. The [INPUT] parameter contains the generic name of the images to process. [DARK + OFFSET] is the name of sum of the dark current image and of the offset signal. So, the dark image has either to be obtained in the same conditions as the images themselves (same exposure time, same temperature), or to be computed (see the OPT command). [FLAT] contains the flat-field image. [OUTPUT] is the generic name of the output images. See also: FULL_PR

The command PR produce preprocessed images that may be, for example, combined later after registration (see REGISTER, ADD2, ADD3, DRIZZLE, COMPOSIT, SMEDIAN, FULL_PR commands). Click here for details.

PREGISTER [IN] [OUT] [SIZE] [NUMBER]
Performs the registration of [NUMBER] planetary images having the generic name [IN] using an intercorrelation method. The size for the intercorrelation is given by [SIZE]. It must be a power of 2 (128, 256, 512...). The size should be larger than the planet diameter. [OUT] is the generic name of the output images. Before use PREGISTER define a selection rectangle around the planetary disk (drag with the mouse). Note that the size of rectangle is not important (the rectangle mark only the center of interest of the image).

Example: PREGISTER MARS I 256 7

To verify the efficiency of this command, you may subtract an image from another one, e.g.:

LOAD I1
SUB I3 2000
VISU 3000 1000

The observed residuals mainly come from the atmospheric turbulence.

See here for an application example.

PREGISTER2 [ENTERED] [LEFT] [SIZE] [A] [NUMBER]
Very similar function that PREGISTER for the registration of the planetary images by the technique of the intercorellation in the Fourier domain. PREGISTER relative make registration of each image of the sequence to the first image of this sequence. PREGISTER2 on the other hand calculates the intercorellation of the image of row N relative with the image of row N-1. This is of an interest when the detail which is used to center the images changes of form notably (a solar protuberance for example).

PREREGISTER [IN] [OUT] [NUMBER]
Command for fast registering of a sequence image. The algorithm is fast (special cross correlation in the spatial domain) but less precise compared to REGISTER, PREGISTER, or CREGISTER for example (PREREGISTER use a registration at the nearest pixel for minimal degradation of image quality) . PREREGISTER is used as a first step registration for difficult case (if traditional registration command are not applicable - situation of large de-registration for example). Applied command like REGISTER or COREGISTER for a second pass (registration at a pixel fraction). Parameters:

[IN] generic name of the input sequence
[OUT] generic name of the output sequence
[NUMBER] image number

Before run PREREGISTER select with the mouse a rectangle around a contrasted details. For important de-registration do not hesitate to select the whole image.

PROD [NAME] [COEF]
Performs the multiplication pixel by pixel of the current image by the image [NAME]. The result is muliplied by [COEF]

Example: To calculate the square of the image M51.PIC:

LOAD M51 PROD M51 .05 VISU 10000 0

PUT [X] [Y] [V]
Attributes the intensity [V] to the pixel at coordinates ([X], [Y]). See also: GET

QR [NAME1] [NAME2] ( or QREGISTER [NAME1] [NAME2] )

Command for a quick and a easy registering of deep-sky image pairs. The method used involve interactively identifying common point sources (stars) in overlapping images fields. This functions are compatible with 16-bits (black & white) and 48-bits images (true colors). [NAME1] and [NAME2] are the file name of the images to be register. The reference is the image [NAME1]. The QR command applied a sample translation to the image [NAME2] for superposition. Click here for details.

QR2 [NAME1] [NAME2] ( or QREGISTER2 [NAME1] [NAME2] )

Command for a quick and a easy registering of deep-sky image pairs. The method used involve interactively identifying common point sources (stars) in overlapping images fields. This functions are compatible with 16-bits (black & white) and 48-bits images (true colors). [NAME1] and [NAME2] are the file name of the images to be register. The reference is the image [NAME1]. The QR2 applied an affine transform to the image [NAME2] for superposition. Click here for details.

RAINBOW [NAME] [LAMBDA1] [LAMBDA2]
Useful for the representation of the spectral data. Colorize with the rainbow colors the image [NAME]. The coloured distribution is realistic and takes into account which the first pixel on the left is with the wavelength [LAMBDA1] and which the last pixel on the right is with the wavelength [LAMBDA2].

REC2SKY [X] [Y]
REC2SKY returns the equatorial coordinates of a point on the image whose Cartesian coordinates in pixels are in the parameters ([x],[y]), using the polynomial files POLX.POL and POLY.POL (created by Astrometry/Photometry dialog box).

Example:

REC2SKY 12.67 321.12

Calculates the equatorial coordinates of the point with Cartesian coordinates (12.67, 321.12) from the parameters contained in the files POLX.POL and POLY.POL.

REGISTER [IN] [OUT] [NUMBER]
Registers [NUMBER] images of a sequence having the generic name [IN] with respect to the first one. The generic name of the output images is [OUT]. The registration consists here in a simple translation.

Draw a rectangle with the mouse around an isolated, non-saturated star. The registration of the images will be done with respect to that star. The size of the rectangle has to be large enough so that it contains the displacement of the star between two contiguous images (if this not the case, Iris could take a wrong star to perform the registration).

Example: REGISTER I J 7

Registers the images I1.PIC ... I7.PIC and produces the output images J1.PIC ... J7.PIC.

The registration is generally followed by a combination of the images (see e.g. ADD2, ADD3 or COMPOSIT). Click here for an example.

REINDEX [IN] [OUT] [FIRST INDEX IN] [FIRST INDEX OUT] [NUMBER]
Reorganize the indices of a sequence. Let us suppose a sequence: I1, I2, I3, I4. One wants to transform it into a sequence J5, J6, J7, J8. One will write:

REINDEX I J 1 5 4

The input and the output sequences cannot have the same name. [NUMBER] is the number of image to be converted.

REMOVE@
Delete all the files of the working directory starting with the character @. Equivalent with command DOS: DEL @*.*

REPAIRX [X]
Replaces the column of rank [x] by the average of the columns of rank [x]-1 and [x]+1. See also REPAIRY.

Example: REPAIRX 66

Replaces the column of rank 66 by the average of columns 65 and 67.

REPAIRX is used for the cosmetic correction of images: suppressing electronic interference or a defective line in the detector.

REPAIRX2 [IN] [OUT] [X] [NUMBER]
Same as REPAIRX but for an image sequence.

REPAIRY [Y]
Replaces the line of rank [Y] by the average of the columns of rank [Y]-1 and [Y]+1.

Example: REPAIRY 90

REPAIRY2 [IN] [OUT] [Y] [NUMBER]
Same as REPAIRY but for an image sequence.

RESET
Update position of dialog box (command , threshold, ...). Useful when the screen resolution is modified.

RGB2HSI [R] [G] [B] [H] [S] [I]
The RGB2HSI command converts an image defined by its Red, Green, and Blue components into an image defined by its Hue, Saturation and Intensity components.

The starting element is a trichromatic image whose three components have been obtained in distinct spectral bands (not necessarily red, green, blue). The names of these images are in the parameters [R], [G], AND [B].

Starting from these three images, RGB2HSI produces three new images:

An image [H] that expresses the hues of the trichromatic image in a gray scale. In this image, pixels that are predominantly red in the trichromatic image will be represented by high levels, pixels that are predominantly green will be represented by intermediate levels, and pixels that are predominantly blue will be represented by low intensity levels.
An image [S] that expresses the saturation of the colors in the trichromatic image in a gray scale. The areas of the trichromatic image where the colors are purest will be represented by the high levels in S.
An image [I] that expresses the average intensity of the three components in a gray scale. The I image is the one that most resembles each of the monochromatic components of the trichromatic image.

See also: HSI2RGB, LRGB, RGB2PCA, PCA2RGB, TRICHRO

RGB2PCA [R] [G] [B] [C1] [C2] [C3]
The RGB2PC1 command (PCA = "Principal Component Analysis") corresponds to a coordinate transformation of a trichromatic image that is represented in the space of fundamental colors (Red, Green, Blue). After the transformation, the axes are the eigenvectors of the covariance matrix of the three input images. The three resulting images are obtained by projecting the three starting axes (R,G,B) onto the three resulting axes. Without going into the mathematical details, it is interesting to choose this coordinate system because it defines three new images that are as uncorrelated from each other as possible, from the chromatic point of view. The matrix of eigenvectors, as well as the associated eigenvalues, are stored in a separate text file (pci.lst).

The first axis, also called the principal axis, corresponds to the largest eigenvalue of the covariance matrix. Generally, this axis is very close to (but not coincident with) the "achromatic axis" (which is the axis of the I image in the RGB2HSI command). This axis contains most of the intensity information and is often close to the average of the input images..

The two other axes (ordered in decreasing eigenvalues) can thus be interpreted as linear combinations of the input images that lead to information that is not correlated to the first axis or to each other. The two corresponding images generally have much weaker dynamics, and are centered around zero. These images thus have a rather low signal to noise ratio, especially for deep sky images, and sometimes require a low pass filter (median type, for example) in order to be correctly visualized.

The interest in this transformation is twofold:

(1) First, visualizing the three images in principal components allows a hierarchical classification of the information contained in the starting trichromatic image. This visualization can be done independently, or trichromatically (by putting the image of the first eigenvector in red, the second in green, and the third in blue). In this case, it is clear that the resulting image is not at all representative of the "true" colors of the image, nor is it very aesthetic, but it is the representation that gives the optimal visualization of the chromatic information in the image.

(2) Second, processing can be done in the space of principal components (primarily adaptations of the dynamics and filtering) and the results can then be brought back to the starting space (R, G, B) (with the PCA2RGB command) to obtain a visual improvement in the original trichromatic image. It is worth noting that for this particular manipulation, the transformation is not as rigorous as the commands (RGB2HSI, HSI2RGB), and is trickier to use. It is generally reserved for images with a good signal to noise ratio (for example, planetary images or bright planetary nebulae).

See also: PCA2RGB, RGB2HSI, HSI2RGB, LRGB, TRICHRO

RGRADIENT [XC] [YC] [DR] [DALPHA]
Computes the rotational gradient of an image. Starting from an input image (in memory), RGRADIENT creates two images, with a radial shift ([dr] in pixels) and a rotational shift ([dalpha] in degrees) with respect to the point ([xc], [yc]). Between these two images, the shifts have the same amplitude, but opposite signs. The two images are then added to create the final image.
In polar coordinates (r, a) with respect to the point ([x],[y]), we have:

B'(a,r,da,dr) = 2.B(a,r) - B(a-da, r-dr) - B(a+da, r-dr)

with:

B = the starting image
B' = the resulting image
da = the parameter [dalpha] of the command
dr = the parameter [dr] of the command

The RGRADIENT command can be executed also from a dialog box (Processing menu).

The rotational gradient is used to observe poorly contrasted details in a bright object which exhibits a symmetry of revolution (dust in an elliptical galaxy or jets in the tail of a comet). The gradient removes the object with a symmetry of revolution with respect to ([x], [y]). Click here for a typical application.

RING_MEDIAN [RADIUS]
Use a particular version of median filtering in order to eliminate from the image of large sizes. The value of the parameter [radius] must be roughly the size in pixels of the objects which one wishes to erase.

RL [#ITER] [COEF]
Restores an image using the Richardson-Lucy method. [#ITER] is the number of iterations to be performed (typically between 10 and 50). If [COEF]=0, the original Lucy algorithm is applied. If [COEF]>0, a relaxation method is used to reduce noise, but convergence is slower. Before running the command, lower the level of the sky background to a level close to zero (use the OFFSET command, the BG command allows you to measure this level). Then choose with the mouse (small rectangle around a star) an isolated, non-saturated star, then run the command, e.g.:

RL 15 0

It is recommended (but not mandatory) that the image has a square size equal to a power of 2 (128, 256, 512...). See here for examples.

RL2 [NB ITER] [COEF]
Modified version of the Richardson-Lucy deconvolution algorithm. The difference with command RL comes from the reduction of granular structure and ringing effect around the bright point-like objects. The reconstruction is effective only for pixels which have an intensity higher than the computed sky background. Just like RL, RL2 command use Fourier transforms and it is recommended to crop the image so that these with dimensions has a size equal to a power of 2 (128, 256, 512 pixels). Use for that WINDOW3 command, especially designed to isolate a squared part of an image. RL2 is used like RL (select with the mouse an unsaturated star before run it). Click here for an example.

ROT [XC] [YC] [ANGLE]
Rotates the current image around the point ([xc], [yc]) by the angle [angle]. The center of the rotation can be off the screen. Note that the coordinates of this center can be noninteger. [angle] is in degrees.

The rotation of an image is used to orient an image with respect to a reference direction (towards the north, for example). ROT is also used with TRANS and SCALE to register images taken with different instruments.

In the following example, we will rotate the image M51.PIC, then go back to the initial orientation:

LOAD N2207
ROT 100 130 22.3
ROT 100 130 -22.3

ROT2 [IN] [OUT] [XC] [YC] [ANGLE] [NUMBER]
Same as ROT but for a sequence of images.

RREGISTER [IN] [OUT] [SIZE] [NUMBER]
Command RREGISTER carries out the registration of a sequence of images of the deep sky by taking of account an accidental field rotation. The principle of the command rests on the pointing of two stars of the fields rather distant from each other but present in all the images of the sequence. The first selected star will be used to carry out registration in translation and will also be used as pivot at the time of the following phase of angular registration (the first star is the center of rotation). The position of second star pointed compared to first star is used to calculate the swing angle of field from one image to another. If possible it is necessary that the stars are not saturated (i.e. too brilliant) to reach a maximum precision.

The pointing of two stars is carried out by using the Select objets command of the Analysis menu. It is only after the two pointed stars operation (click with the mouse) that you can run command RREGISTER. Parameters:

[IN] is the generic name of the sequence of images to be treated.
[OUT] is the generic name of the centered images.
[SIZE] is the size in pixel of with dimensions of a rectangular surface which must contain at least stars pointed between two successives images of the sequence. This size is all the more large since the displacement of the successive images is significant.
[NUMBER] is the number of images of the sequence.

For an application, click here.

SAVE [NAME]
Save the image in memory in the current directory (defined in the item Current Directory from the Settings tab). You can also indicate in which directory to save a particular image by specifying the full path of the image. For instance: save c:\nuit7\m51

SAVE_TRICHRO [R] [G] [B] (or SAVE_TR [R] [G] [B])
Save the colors layers of the current displayed true color image into three distinct file.

SAVEBMP [NAME]
Save the image in memory in the current directory under the form of a bitmap file. The color palette used to create the file is the active palette. The BMP image is a 24-bits images if a tri-color is loaded (see TRICHRO command).

SAVEJPG [NAME] [QUALITY]
Save current image into a JPEG file. You have the possibility to adjust the compression factor. A value 1 for quality parameter offers best fidelity. A quality of 5 corresponds to the maximum compression ratio. It is also possible to produce an JPEG image from the Save... function of File menu.(quality = 2).

SAVEPPM [NAME]
Store current image in the form of a PPM file (Portable Pixel Map - 24-bits format). You can save true colors images (24-bits) but also, black and white images (16-bits)

SAVEPSD [NAME]
Save the in-memory image into a Photoshop PSD 48-bits file (16-bits by color plane). Note: The image must not contain any negative pixel values for this function to work correctly. See CLIPMIN, OFFSET, and MULT.

SBLUR [ SIGMA] [GAMMA ]

Command SBLUR (for Selective Blur i) generates a blur in the image with a force more higher since the objects are more intense. This function is used on star fields to produce an Akira Fujii effect, for example to reveal the contour of the constellations. The parameter SIGMA permit to adjust the degree of the blur (select values between 2 and 15) and the parameter GAMMA makes adjust the sensitivity to the brightness of stars (the characteristic value is between 4 and 10). For an optimal effect it should be taken care that the most brilliant stars are not saturated. This command boost the colors and can be also used in combination with ASINH. Click here for examples.

SCALE [OPTION] [XF] [YF]
The SCALE command can be used to enlarge or reduce the current image. Each axis can have a different scale factor.

The parameters are:

- Type of interpolation:

- [option] = 1, for an enlargement, interpolation by pixel duplication; for a reduction, interpolation by undersampling
- [option] = 2, bilinear interpolation
- [option] = 3, spline interpolation (only for enlargements).

- [xf] = scale factor along the X axis

- [yf] = scale factor along the Y axis.

The SCALE command can be used to detail regions of an image by enlarging it. Some types of processing, like restoration, photometry, and astrometry, become more precise when the image is oversampled. You can artificially oversample with the SCALE command.

Reducing images is also useful when they take up too much space, or to build a library of quick-look images (where only an approximate look is important).

To see the influence of the different types of interpolation, execute the following commands:

LOAD M51
SCALE 1 3 3

Interpolation by pixel duplication conserves the sharpness of the image, but of course the result has an artificial look.

LOAD M51
SCALE 2 3 3

Bilinear interpolation gives the image a smoother look than simple pixel duplication. Nevertheless, for large enlargement factors, some artificial geometric structures can appear around stars. The spline interpolation reduce this effects.

LOAD M51
SCALE 3 3 3

Try also:

SCALE 2 2.7 0.76

SCALE2 [IN] [OUT] [OPTION] [XF] [YF] [NUMBER]
Same function that SCALE but applies to a sequence of images.

SCALECOLOR [IN] [OUTPUT] [REFERENCE INDEX] [NUMBER]
Scale the input images sequence [I] for color combining (or drizzling algorithm). For each images, a rescaled sky was substracted and a gain ajusted relative to a reference image of the input sequence. The index of the reference image is [REFRENCE INDEX]. The generic name of the output sequence is [OUTPUT].

Before SCALECOLOR command select an unsatured star with the mouse (the images are to be registered before applying SCALECOLOR, see REGISTER or COREGISTER for example). Idealy, for a good color balancing, select a solar type star (a G star).

Example:

SCALECOLOR I J 2 3
Scale the images I1, I2, I3 relative to the image I2. This produce the scaled sequence J1, J2, J3. If J1 is the R component of a tricolor image, if J2 is the G component and J3 is the B component, than you can made:

TRICHRO J1 J2 J3

SCALECOLOR2 [R] [G] [B]
Adjust the respective levels of the images [R], [G], [B] so that their intensities are identical on average in a zone of the image defined as a preliminary with the mouse. More precisely, Iris multiplies the images [G] and [B] by a distinct coefficient and their additions a constant to equalize them with the image [R]. This command is very practical to carry out the chromatic balance of the planetary images (click here for an example). For the stellar images it is necessary to employ command SCALECOLOR.

SCAN [X1] [Y2] [INTEGRATION TIME] [LINE NUMBER]
Acquisition in scan mode (TDI) since a Audine camera. Click here for more details.

SCAN2PIC [NAME] [X0] [NUMBER]
Select the column of coordinate [X0] in the first image of a sequence of [NUMBER] images of generic name [NAME]. This column becomes the first column of a new image which is built in the memory of the computer. The column of coordinate [ X0 ] in the second image of the sequence becomes the second column of the image in memory, and so on for all the images of the sequence. Finally, the image in memory, and which is displayed after the processing, has a horizontal format equal to the number of images of the sequence and a vertical format equal to the number of pixels along the axis Y in the images of the sequence.

A use of SCAN2PIC is the synthesis of a monochromatic image of the Sun while scanning its disc on the entrance slit of the spectrograph and by making a regular acquisition of images simultaneously. These images become the input sequence of SCAN2PIC. The coordinate [X0] is for example the core of a spectral line (the H-alpha line in the red for example) or the close continuum if one want an image standard photosphere. Click here for an illustration of this principle.

It is necessary if possible to adjust the frequency of acquisition of the images with the scanning speed if one want that the scale of the image is the same following axes X and Y. The final improvement of a different scale along the axes is possible with SCALE command which acts independently as X and Y. Command WIN_WEBCAM is useful to isolate the strictly necessary of the image during acquisition (some pixels on the right and on the left of a spectral line for example).

SCAN_CALIB [NAME] [NUMBER]
Method of synchronization of PC time. Click here for an application example.

SETBASE [BASE]
Define the first index for an input sequence for the commands CONVERTBMP, CONVERTBMP24, CONVERTBMP24BW, CONVERTTIFF, CONVERTTIFF24 and CONVERT24BW. The default value is 1. The over typical value is 0. For this enter the command:

SETBASE 0

SETFINDSTAR [SIGMA]
Define the threshold above the noise for stars detection with FINDSTAR and COREGISTER commands. The RMS noise in the background image is determined, then the threshold is : [SIGMA] x (RMS noise). The default value for SIGMA is 7. Example:

SETFINDSTAR 10
set the sigma coefficient to 10.

SETREGISTER [POLYNOM ORDER]
Define the order of the polynom for registration with the COREGISTER command. The default is a polynom of degree one. If it is necessary to correct distortion between images you can increase this value. The max value is 5. Example:

SETREGISTER 2
set the polynom to the order2.

SETSPLINE [MODE]
If you carry out command SETSPLINE 0 all operations of registrations run since the line of commands use the bilinear interpolation to calculate the registered images. If you carry out command SETSPLINE 1 same the operations use the spline interpolation method. The advantage of the spine interpolation spline is a less smooth of the images and thus a better preserved details. On the other hand the calculating time is longer. The commands concerned are for example REGISTER, PREGISTER, CREGISTER, RREGISTER. For the simple translation or the simple rotation of the image in memory you can use commands STRANS and SROT to profit from the spline interpolation spline (symmetrical functions the TRANS one and ROT which use they a bilinear interpolation). The profit of the spline mode is particularly visible in deep sky imagery.

The interpolation spline was already present in the preceding version of IRIS, but only for the accessible commands since the menus (for example the command Registration of stellar images... of Processing menu).

SETSUBSKY [SIGMA] [POLYNOM ORDER]
Define the polynom order for the fit of the sky with the SUBSKY command and the threshold above the noise for backgound detection. The default value are standard for the majority of situations (SIGMA=5, POLYNOM ORDER=3). Example:

SETSUBSKY 8 1
set the fit to order to one and the sigma coefficient to 8.

SET_DATE [DATE]
Modify the date of acquision of an image. Example: SET_DATE 16/09/2000

SET_FITS [BSCALE] [BZERO]
If necessary define manually the parameters BSCALE and BZERO before loading a FITS image (for example for fit the dynamics to the authorized range for Iris [-32768..32767] for difficult case like no full compatible FITS header).

SET_HOUR [HOUR]
Modify the hour of acquision of an image. Example: SET_HOUR 20:05:45

SIGNED
Convert 16 bits unsigned in-image to a 16 bits signed image. Usefull for some imported images. See also: LOADSX, CONVERTSX.

SKY2REC [RA] [DEC]
Starting from the polynomial files POLX.POL and POLY.POL (created by Astrometry/Photometry dialog box), SKY2REC returns the Cartesian coordinates of a point on the image whose equatorial coordinates are in the parameters ([alpha], [delta]).

SKY2REC 8H34M20.3s –05d12’34"

SLANT [Y0] [ALPHA]
Rectification of tilted stellar spectra. See here for an application.

SLANT2 [INPUT] [OUTPUT] [Y0] [ALPHA] [NUMBER]
Equivalent to SLANT, but for an images sequence.

SMAX [NAME] [NUMBER]
For a given pixel in the output image, SMAX calculates the maximal of the intensities of the corresponding pixels in a set of images whose generic name is in the parameter [name]. The number of image in the stack is [number]. See also: SMIN.

SMEDIAN [NAME] [NUMBER]
For a given pixel in the output image, SMEDIAN calculates the median of the intensities of the corresponding pixels in a set of images whose generic name is in the parameter [name]. The pixel in the output image is set to the value of the median intensity.

The generic name is the root of the name of an image which is completed by a number and an extension. The first number added is 1 and the last is [number]. Thus, with the generic name "image" and [number]=5, the processing will act on the images:

IMAGE1.PIC
IMAGE2.PIC
IMAGE3.PIC
IMAGE4.PIC
IMAGE5.PIC

Recall the definition of the median. Start with the set of numbers:

5, 9, 1, 0, 3

Arranging these numbers in an increasing order gives:

0, 1, 3, 5, 9

The median value is the number 3.

At the end of the calculations, SMEDIAN provides the percentage of the contribution from each input image to the final median image.

The maximum number of images is 19 (see also: SMEDIAN2).

Exemple: SMEDIAN IMAGE 5

The principal application of SMEDIAN is the calculation of a flat-field from a sequence of images containing stars. For the flat-field to be correct, the field of view should be different for each image in the sequence. This way, the median flat-field will not have stars, since there is little chance that a star would be on the same pixel on all the images in the sequence if the number of images is relatively high (greater than or equal to 5).

On the other hand, SMEDIAN can be used on a set of centered deep sky images. In this case, you obtain an image with the same density as an individual image, but on which most of the artefacts have been eliminated (electronic interference, cosmic rays, satellite tracks, etc.).

Before calculating the median image, it is important for each image in the set to have the same signal level (see NGAIN2 anf NOFFSET2 commands).

It is good to compare this image with one of the individual images to see that in the flat-field image the stars have totally disappeared and the noise is noticeably attenuated.

It is important to study the contribution of each input image to the median image. Ideally, the percentage for each image would be identical. In this case, since we have used 5 images, the percentage for each one should be about 20%. Any significant difference is a sign of an anomaly. This is one way to find that an image is not homogeneous with respect to the others (bad offset, for example).

Click here for a typical application example.

SMEDIAN2 [NAME] [NUMBER]
Same command as SMEDIAN, slower but unlimited as far as the number of images is concerned.

SMILE [Y0] [RADIUS]
Change the curve of the spectral lines to compensate an distortion optical defect of smile type, a traditional problem in spectrograph. The parameter [RADIUS] is the radius of curvature of the spectral lines. [Y0] is the vertical coordinates corresponding to the vertex of the curve. For an example, click here.

SMILE2 [IN] [OUT] [Y0] [RADIUS] [NUMBER]
Same command that SMILE but applying to a sequence of image. This makes it possible to correct the distortion of the spectral lines in order to make them quite right, which is in particular significant in a command like SCAN2PIC during the synthesis of a spectroheliogramme of the Sun.

SMIN [NAME] [NUMBER]
SMIN calculates the minimal intensities of a stack of [number] images of generic name [name]. Click here for an application. See also: SMAX.

SQR [NAME1] [NAME2] ( or SQREGISTER [NAME1] [NAME2] )

Same as QR command, but use spline interpolation. Click here for details.

SQR2 [NAME1] [NAME2] ( or SQREGISTER2 [NAME1] [NAME2] )

Same as QR2 command, but use spline interpolation. Click here for details.

SROT [CX] [CY] [ANGLE]
Command similar to ROT but using the spline interpolation instead of the bilinear interpolation. SROT makes it possible to obtain images having a factor of smoothing less significant than ROT, which preserves resolution.

STAT
Return global statistic of the image.

STRANS [DX] [DY]
Command similar to STRANS but using the spline interpolation instead of the bilinear interpolation. STRANS makes it possible to obtain images having a factor of smoothing less significant than TRANS, which preserves resolution.

SUB [NAME] [OFFSET]
Subtract to the image in memory the image on disk designated by [neme]. The constant value [offset] is added to the result.

SUB2 [IN] [OPERAND] [OUT] [OFFSET] [NUMBER]
Subtracts from the [number] images of a sequence of images with the generic name [in] the image [operand] then adds the value [offset] to these images (see the command SUB). [out] is the generic name of the output images.

SUBSKY
Computes the level of the local sky background and subtracts it from the image. The level is determined from 2000 points in the image (avoiding stars and galaxies). From these measures, by default, a 3rd-degree polynom is computed that fits the sky background. A synthetic image is then created and subtracted from the original one. See also: SETSUBSKY.

SUBSKY2 [IN] [OUT] [NUMBER]
Same as SUBSKY but for a sequence of NUMBER images.

SUBSTITUTE [NAME1] [MAME2] [DELTA]
Performs the pixel by pixel comparison of the images [NAME1] and [NAME2], and for each of these pixels:

if ABS([NAME1]-[NAME2])>[DELTA] then
    result = [NAME2]
otherwise
    result = [name1]

(ABS signifies absolute value).

The SUBSTITUTE command is used in conjunction with the image modeling commands (i.e. FIT ELLIPSE command) in order to suppress the stars in the original image. This creates a new image that is better analyzed after a second pass.

There are three steps:

Build a rough model of the original image;
Apply SUBSTITUTE in order to produce an image that is close to the original, but where the zones that are difficult to model (stars, etc.) are replaced by their equivalent in the calculated model;
Calculate a second model from the image determined in the preceding step. This model is generally more satisfactory than the first.

SYM [CX] [CY]
Copies a part of an image into another part of this image symmetrically with respect to the point ([cx],[cy]). The window to copy has to be drawn first with the mouse.

Symmetry with respect to a point is used to suppress an undesired object in an image. The area containing the object is replaced by a similar area taken from the same image. The duplicated area should not, of course, contain undesirable objects itself. For a deep sky image, make sure that the sky background has the same value in the two zones. The SYM command can be used to erase certain defects in an image (cosmic rays, etc.). It is often used in conjunction with the FIT ELLIPSE command to suppress the bright stars in the object to be modeled.

For exemple, let's suppress the star in front of the elliptical galaxy UGC 4170 (see here a tutorial) at the coordinates (50,91). Using the cursor, we find that the center of the galaxy is, to within a pixel, (66, 103). The process is the following:

LOAD U4170
VISU 560 370
Drag the star
SYM 66 103
VISU 560 370

SYNTHE
Synthetizes an image from polynoms created by the command POLY.

The whole procedure is as follows:

- Load the image to processs and visualize it.
- Type POINTON
- Select hundreds of points avoiding stars and any object in the field.
- Compute the polynoms, e.g. by typing POLY 3
- Synthetize the background by typing: SYNTHE
- Save the synthetic background, e.g. SAVE SKY
- Reload the original and subtract the background (add a constant to make the visualization easier): SUB SKY 500
- Go back to standard mode: POINTOFF

Click here for an example.

See also: SUBSKY that performs all these procedure with a single command.

T_ADD [R] [G] [B] [NUMBER]
Addition of the images of each color planes (equivalent ADD2). Operation carried out:

(R1+R2+..+Rn, G1+G2+..+Gn, B1+B2+..+Bn) -> [R], [G], [B]

For application examples of T-Tools commands, click here.

T_ADD_NORM [R] [G] [B] [NUMBER]
Even operation that T_ADD but standardizes the images on level 32000 with the need if this level is exceeded (equivalent ADD_NORM).

T_COMPOSIT [R] [G] [B] [SIGMA] [NB ITER] [FLAG MAX] [NUMBER]
Produce three images [R] [G] and [B] by making an optimal addition of the images of the sequences R1... Rn, G1... Gn, B1... Bn (equivalent COMPOSIT). The procedure is iterative if [NB ITER] is higher than 1. The threshold of rejection of the bad values is adjusted by the variable [SIGMA] (typical real value between 2 and 3). Level 32000 after addition is not exceeded if FLAG MAX = 1 (a normalization of the intensities is done). Limited to 19 input frames.

T_COPY [in R] [in G] [in B] [out R] [out G] [out B] [NUMBER]
Duplicate a trichromatic sequence. Carry out the operation:

(in R1... in Rn, G1... in Gn, B1... in Bn) -> (out R1... out Rn, out G1... out Gn, out B1... out Bn)

T_CREGISTER [THRESHOLD] [NUMBER]
Registration of planetary images by adjusting a circle on level [THRESHOLD] around planet limb (equivalent to CREGISTER).

T_DIV [R] [G] [B] [NUMBER]
Divide the sequences R1... Rn, G1... Gn, B1... Bn by the images [R], [G] and [B] (equivalent has DIV, but the parameters of standardization is calculated automatically in T_DIV). Carry out the operation:

(R1/[R]... Rn/[R], G1/[G]... Gn/[G], B1/[b]... Bn/[B]) -> (R1... Rn, G1... Gn, B1... Bn)

T_GAUSS [SIGMA]
Convolution by Gaussian of the trichromatic image defined by the file R, B and B. Equivalent to command GAUSS2.

T_MULT [coef R] [coef G] [coef B] [NUMBER]
Multiply each image of the sequences R1... Rn, G1... Gn, B1... Bn by constants (equivalent with MULT2). Carry out the operation:

(R1*[coef R]... Rn*[coef R], G1*[coef G]... Gn*[coef G], B1*[coef B]... Bn*[coef B]) - > (R1... RN, G1... Gn, B1... Bn)

T_NGAIN [NORM] [NUMBER]
Multiply each images of the 3 sequences by a constant calculated by Iris in manner what the median level of each image is equal to [NORM] (equivalent with NGAIN2). This command is in particular used for stack flat-field images before median composite.

T_NOFFSET [NORM] [NUMBER]
Add (or subtract) to each images of the three sequences a constant calculated by Iris in manner what the median level of each image is equal to [STANDARD] (equivalent NOFFSET2). Useful to bring at the same the level the sky background on deep-sky images.

T_OFFSET [offset R] [offset G] [offset B] [NUMBER]
Add a constant to each images of the sequences R1... Rn, G1... Gn, B1... Bn (equivalent with OFFSET2). The constants can have negative values. Carry out the operation:

(R1+[offset R]... +.Rn+[offset R], G1+[offset G]+... +Gn+[offset G], B1+[offset B]+... +Bn+[offset B]) - > (R1... RN, G1... Gn, B1... Bn)

T_PREGISTER [SIZE] [NUMBER]
Equivalent with PREGISTER for the registration of the planetary images. Registration is calculated on the sequence G1... Gn then is the parameters of translation are applied to the sequences R1... Rn, B1... Bn. It is thus supposed that it is the green component of the three-colour process which presents the best details and contrasts.

T_PREREGISTER [NUMBER]
Equivalent with command PREREGISTER.

T_REGISTER [NUMBER]
Equivalent with command REGISTER. Ideal for the deep-sky images (uses the position of a reference star to be selected in the first images of one of the series, image G1.FIT for example).

T_RESTORE
Carry out the opposite operation of T_STORE : restore in the files image R, G and B the contents of file # R, # G and # B.

T_SCALE [OPTION] [FX] [FY]
Change the scale of a trichromatic image defined by the files R, G and B. Same parameters as command SCALE.

T_SELECT
Simultaneous sort by decreasing quality the images in the red, green and blue planes (equivalent to SELECT). It is necessary to have run before command BESTOF on one of the components trichromatic (the green one for example).

T_SMEDIAN [R] [G] [B] [NUMBER]
Median stack of the sequences R1... Rn, G1... Gn, B1... Bn by producing the images [R] [G] and [B] (equivalent with SMEDIAN). Algorithm fast but limited to 19 images.

T_SMEDIAN2 [R] [G] [B] [NUMBER]
Even function that T_SMEDIAN, slightly slower but the number of images is unlimited (equivalent to SMEDIAN2).

T_STORE
Copy the three images having for name R, G and B respectively in files # R, # G and # B.

T_SUB [R] [G] [B] [NUMBER]
Subtract the images [R], [G] and [B] to the sequences R1... Rn, G1... Gn, B1... Bn (equivalent with SUB2 or SOUST2). Carry out the operation:

(R1-[R]... Rn-[R], G1+[G]... Gn+[G], B1+[B]... Bn+[B]) - > (R1... Rn, G1... Gn, B1... Bn)

T_TRICHRO or T_TR
Display a color image color from the files images R, G and B.

T_UNSHARP [SIGMA] [COEF] [FLAG]
Display a color image starting from the files images R, G and B, but applies a unsharp masking filter with each components as a preliminary. Same parameters as command UNSHARP.

T_UNSHARP2 [SIGMA] [COEF] [FLAG] [NUMBER]
Calculate the unsharp masking of each images of the three sequences (equivalent with UNSHARP2).

TCL [SCRIPT] [PARAMETER₁] [PARAMETER₂] ... [PARAMETER_N]
Execute a Tcl script. [SCRIPT] is the name of the scripting file in the disk. [PARAMETER1], [PARAMETER2], etc is a variable number of parameters for the script. For details about the powerfull TCL command see the ASTP protocol Web page.

TEXT [TEXT] [X] [Y] [INTENSITY]
Allows to write a text in the image. This function modifies the intensity of the pixels in the 16-bits image. You can retrogress while using the button " undo " tools bar.

[TEXT] is the contents of the text.
[X] and [Y] are the coordinates in pixels of the position of the beginning of the text.
[INTENSITY] is the intensity of the text, a number ranging between 0 and 32767.

Example:

Text Zeta_Tau_____April_2002 30 5 32000

Note the use of the character " _ " to write white.

TH_CUT [IN] [OUT] [HIGH LEVEL] [LOW LEVEL] [NUMBER]
Adjusts thresholds of visualization [HIGH LEVEL] [LOW LEVEL] for a sequence of images having the generic name [IN]. The generic name of the output images is [OUT]. See here an application example.

TIFF2PIC [IN] [OUT] [NUMBER]
Convert a sequence of TIFF file to PIC or FITS sequence.

TILT [X0] [ALPHA]
Rectify a spectrum whose axis of dispersion forms an angle [ALPHA] compared to the horizontal axis of CCD sensor. Calculation is done by vertically shifting each column of the adequate fraction of pixel. The pivot of rotation is located at the horizontal coordinate [X0] counted in pixels. The angle is in degrees and can be signed. Click here for an application.

TIME
Return the actual hour.

TRACK [NAME] [NUMBER]
Analyze a star selected in a sequence of images and produces files DX.DAT and DY.DAT allowing to observe the drift of a telescope according to time.

TRAIL [Y0] [Y1] [Y2]
Align the points of drift star trace or a spectrum. Click to see an application.

TRAIL2
Interactive version of TRAIL, requiring only two clicks of the mouse upper and downer of a star trail or a spectrum to obtain a straight trail or a straight spectrum.

TRANS [DX] [DY]
Translates the current image by [DX] along the X axis and by [DY] along the Y axis. The calculation is performed using bilinear interpolation.

Example: TRANS -12.3 4.02

Translates the image by -12.3 pixels along the X axis and by 4.02 along the Y axis.

Translation is a fundamental tool that is often used to center a set of images with respect to each other so that they can easily be compared and processed (for example, summation of a set of images).

In the following example, translation is used to produce two images which are slightly shifted from each other, starting from the same original. The difference of these two images gives a characteristic bas-relief effect (or gradient effect):

LOAD M51
TRANS 1 0
SUB M51 100
VISU 150 50

TRANS2 [IN] [OUT] [DX (PIX./HOUR)] [DY (PIX./HOUR)] [NUMBER]
Transform a sequence of image into another sequence by making a translation of a certain number of pixels depending on the hour of acquisition of the images and the shift in X and Y specified in parameters (in pixels per hour). The typical use is the centering of a sequence on the movement of a comet or of an asteroid in such a way that this object appears fixed after stacking. One generally proceeds in two times: registration on a star of the field (REGISTER command for example), then, application of the command TRANS2 command. Supposing that the ephemeris (or a direct measurement in the image) teach us that mobile object moves 0.230 pixel/hour in X and of -0.763 pixel / hour in Y in the sequence I1, I2, I3... I20. One obtains a new sequence J1, J2.... J20 where the movement of the object is cancelled while making:

TRANS2 I J 0.230 -0.763 20

Click here for an exemple of the use of TRANS2.

TRICHRO [R] [G] [B]
Load R, G & B 16 bits componants of a tri-color image and vizualise the 24-bits results. Example:

TRICHRO M57R M57G M57B

UNSHARP [SIGMA] [COEF] [FLAG]
The UNSHARP command performs filtering by unsharp masking on the current image.

This type of filtering is high pass: it tries to eliminate the low frequencies in the image, accentuate the high frequencies and then add them, with a weighting factor, to the original image. The process is:

Convolve the image to be processed by a gaussian whose width is in the parameter [sigma] (see the GAUSS and GAUSS2 commands).
Subtract the result of this convolution from the original image. The result is an image with an average level close to zero, and whose low frequencies (slow variations in the image) have been strongly attenuated. At this stage, a positivity constraint can be applied (this sets all the negative values to zero). If [FLAG]=0, the constraint is not applied. This option should be used for processing planetary images. If [FLAG]=1, the constraint is applied. This option should be used for processing deep sky images.
Multiply the result of the preceding step by the constant whose value is in the variable [coef], then add it to the original image. The result is the final image.

Unsharp masking is a very simple, but nevertheless powerful tool for enhancing the contrast of an image. It is one of the basic tools for planetary image processing.

With Iris, unsharp masking can easily be performed with the GAUSS (or GAUSS2), SUB, MULT, and ADD commands. The UNSHARP command simply puts all these operations into one command.

The values of the variables [SIGMA] and [COEF] need to be adjusted by trial and error. As a general rule, a small [SIGMA] (<1) and a large coefficient enhance the finest details, but then the noise may become overwhelming.

UNSHARP2 [IN] [OUT] [SIGMA] [COEF] [FLAG] [NUMBER]
Even command that UNSHARP but for a sequence of images.

UNSHARP3 [SIGMA] [COEF] [EDGE TUNING] [FLAG]
Has a similar effect to the Unsharp Masking... dialog box in the Processing menu. Click here for details.

UNSHARP_TRICHRO [R] [G] [B] [SIGMA] [COEF] [FLAG]
Carry out an operation of filtering of unsharp masking type on the three components of a trichromy image at the same time and display the result.

Syntax is similar to command UNSHARP but it is necessary to provide the name of the three images correspondents to the red, green and blue channel. For example for a planetary image one will do something which resembles:

UNSHARP_TRICHRO R G B 1.8 4 1

VANCITTERT [FWHM] [#ITER]
Restores an image with the Van-Cittert method. [#ITER] gives the number of iterations to be performed (typically between 5 & 20), whereas [FWHM] is the caracteristic FWHM of the stars in the image to restore.

Before running the command, lower the sky backgroug to a level close to zero (use the OFFSET command for example).

Example:
LOAD M51
OFFSET -100
VANCITTERT 1.8 5

VIDEO [X1] [X2] [INTEGRATION TIME] [SIZE OF A BLOCK] [BLOCK NUMBER]
Acquisition in VIDEO mode with the Audine camera. Click here for more details.

VIDEO_GRID [SIZE]
Display in the image a horizontal grid with a step in pixel equal to the value of the parameter size]. This grid is a help to position at the good place objects for the VIDEO mode acquisition (Audine CCD camera). You can also reveal this grid by typing with the keyboard simultaneously the combination of key <Ctrl><F6> (you must have click in the image before).

VISU [HIGH] [LOW]
Display an image with HIGH as the high threshold and LOW as the low threshold.

WAVELET [OUT1] [OUT2] [SCALE]
The WAVELET command performs a wavelet transform on an image. This analysis decomposes the current image into images that each show details of increasing scales. This amounts to multiresolution analysis of the initial image.

The algorithm used in Iris is called "à trous" ("with holes"). It calculates an approximation to the input image by considering only the pixels on the crossings of a mesh whose step varies by a factor of 2 between two scales. In a way, as the scale increases, you see the objects as they would look if you moved away from them by a factor of 2 from one decomposition to the next.

Points that are between the mesh crossings are approximated with an interpolation function - the wavelet. The interpolation is done with a 3x3 matrix. Many classes of wavelets can be defined, but they all have common characteristics (in particular, they are functions with a zero average). Wavelet analysis is a new method for interpreting the contents of images. It studies structures of different sizes in the image, and analyzes their relations. It is called analyzing the hierarchy of structures of the objects in the image.

The decomposition of the image into structures with distinct scales allows the reconstruction of the initial image so that only the pertinent details remain (the algorithm programmed in Iris permits this reconstruction). This yields a very precise filtering of the image. Note also that wavelets are at the core of some image compression algorithms.

The parameter [OUT1] contains the generic name of the approximated images with increasing scales. The number of scales is contained in the variable [scale]. The image with the smallest scale has the index 1, the following 2, and so on.

The parameter [OUT2] contains the generic name of the images corresponding to the difference between two successive approximations (namely the wavelet coefficients). These images contain the details that disappear from one scale to the next (the image with index 1 contains the details from scale 1, the image with index 2 those from scale 2, the image with index 3 those from scale 4, the image with index 4 those from scale 8, and so on).

The number of scales analyzed is in [SCALE]. Typicaly scale=3 to 5.

Let's perform wavelet analysis on the image M51:

LOAD M51
VISU 800 40

Wavelet analysis will allow us to study the relationship between structures with different scales (groups, arms, nucleus, etc.). We will also attempt to enhance the appearance of the groups by reconstructing the image.

Perform the transform:

WAVELET I J 6

The images I1...I6 contain the successive approximations of the image in increasing scales. The images J1...J6 are the wavelet coefficients for the successive scales 1, 2, 4, 8, 16, and 32.

Let's examine the wavelet coefficients for each of the scales:

LOAD J1
VISU 100 -100

It is difficult to recognize the galaxy on this image. In fact, at the scale 1, the image contains mostly noise, which is why it is so uncorrelated with the input image.

LOAD J2
VISU 100 -100

At this scale, the nodules in the arms are brought out.

LOAD J3
VISU 100 -100

The arms start to be continuous. Note the strong hierarchical relationship of the details between this scale and the previous one.

LOAD J4
VISU 100 -100

The large scale structures of the galaxy are becoming evident...

LOAD J5
VISU 200 -200

This trend continues...

LOAD J6
VISU 300 -300

At this last scale, only the massive central part of the galaxy is visible.

You can, of course, examine the corresponding approximations (images I1.PIC, I2.PIC, etc.). The last one is special since it is the residual of the transform. To understand the contents of this images, imagine how the galaxy would look if you moved away from it while you were observing it through a telescope with constant resolution.

It is possible to reconstruct the initial image by adding the set of wavelet coefficients and the residual:

LOAD J1
ADD J2
ADD J3
ADD J4
ADD J5
ADD J6
ADD I6
VISU 800 40

ADD2 J 6
ADD I6

However, since we have seen that the coefficients of the first scale only correspond to noise, it is wise to eliminate the details of this scale from the reconstruction. Also, we want to enhance the contrast of the stellar groups. To do this, we will assign a weight greater than 1 to the coefficients corresponding to the details of scale 2 and 4 (the weighting factors of 2 and 1.5 that we have used are arbitrary; it requires several trials to estimate the best values for a given application):

LOAD J2
MULT 2
SAVE K
LOAD J3
MULT 1.5
ADD K
ADD J4
ADD J5
ADD J6
ADD I6
VISU 800 20

The noise has been noticeably reduced and the contrast increased.

You have probably noticed that the previous process is very similar to traditional unsharp masking. However, one of the fundamental differences is that the unsharp mask is performed with only one scale while the WAVELET command offers a multiscale analysis that acts more finely on the contents of the final result. Click here for some example.

WAVELET2 [OUT1] [OUT2] [SCALE]
Same command WAVELET but uses 5x5 wavelets.

WAVELET_FILTER [NOISE] [COEF] [NUMBER]
Apply a filter to the current image for noise suppression. For this, WAVELET_FILTER use an evolued procedure that limit resolution degration. [NOISE] parameter is the RMS noise in the background of the image (it can be measured with the command Statistics from the contextual menu. [COEF] is a rejection noise factor. Typicaly [COEF] value is between 2 et 4. [NUMBER] is the number of wavelet plane (see WAVELET command). Typicaly [NUMBER] = 5.

Example for M51 image:

LOAD M51
WAVELET_FILTER 7.8 3 5

WDATE
Write the acquisition date in the image. The same effect is obtained while making: Ctrl+F8. For memory, the combination of Ctrl+F9 keys copies the image in the clipboard.

WHITE
To restore just colors of tri-color images it is some time necessary to the balance the white. The version 3.83b integrates two new commands which make it possible to carry out this operation with precision and speed. The second command, WHITE, makes the adjustment of the white itself. The three colors planes are treated simultaneously (as opposed to what made SCALECOLOR2 command). One selects a reputed white area in the image with the mouse (Iris calculates the median intensity in the window). In the case of the planet Mars the polar cap is ideal for that (but attention, one should not have saturated the image at this place due for example to a too long exposure time). Iris turns return the coefficients by which it has to multiply components RGB to adjust the levels in the selected zone. Note that commands BLACK and WHITE must be executed in the order given hereafter. See also the BLACK command.

WHITE2
Harmonize the three layers of a color image (48-bits) by equalizing the intensity of the same star in these layers (multiplication by suitable coefficient). The program carries out a Gaussian adjustment of star. The selected star must be surrounded by a small rectangle before run the command (click here for a typical application). See also the command WHITE which uses the median value of a zone selected with the mouse and the black command for adjust the background level (click here for another example).

WIN
Crop an image interactively. Click with the mouse two points around the area to isolate.

WINDOW [X1] [Y1] [X2] [Y2]
The WINDOW command creates the output image from a window defined in the input image.
The window is here defined with the 2 points ([x1],[y1]), ([x2],[y2]).

Example: WINDOW 23 45 450 640

The WINDOW command allows you to unify the formats of images. This is important when you want to process images coming from different sources.

WINDOW2 [IN] [OU] [X1] [Y1] [X2] [Y2] [NUMBER]
Same command as WINDOW, but applies to a sequence of [number] images having the generic name [IN]. The generic name of the output images is [OUT].

WINDOW3 [SIZE]
The WINDOW3 command allows you to isolate a square area of size [size] in an image. You have to define first the center of the window by drawing a small rectangle around it with the mouse. The WINDOW3 command is useful to prepare images for which size has to be a power of 2 (see for example PREGISTER command).

WINDOW4 [IN] [OUT] [SIZE] [NUMBER]
Same function that WINDOW3, but applying to a sequence of images.

WIN_WEBCAM [X1] [Y1] [X2] [Y2]
Defined coordinates of a window in the images resulting from a webcam source and acquired with the command Images acquisition of Webcam menu. Let us suppose for example that the format of the images is 320x240 pixels (Size of the images... from Webcam menu. If before launching acquisition you type in the console:

WIN_WEBCAM 100 1 120 240

then, all the acquired images (including in sequence mode of course) will have a size of 20x240 pixels, isolating in the full format image a sub-images delimited by the coordinates (100,120)-(1-240). To reset the full format you must in this example type in the console:

WIN_WEBCAM 1 1 320 240

(the effect is similar if you leave, then enter the program).

The interest of WIN_WEBCAM is a substantial saving in place on the disc if the object observed is of small size compared to the format of the image. The speed of acquisition is also increased. Another typical application is the acquisition of large number of images of a spectral line of the Sun whereas the disc of this one travels on the input slit of the spectrograph. It is in this manner possible to reconstitute a monochromatic image of the Sun (see command SCAN2PIC).