An image must be read into XIMAGE using either read_image or simulate. The former is used if the image is taken from a specifed file that can be:
If a photon event file is available then this can also be read in to create an image using the read/rfits command. Currently only the ROSAT FITS format is supported. Various default image sizes have been established for each mission, that can be changed using the /size and /rebin qualifiers.
Once an image has been loaded it is displayed using the display command, but first the plot device must be set using the cpd command. XIMAGE supports many different plot devices, though the best performace is obtained using x windows. On VMS use cpd /x11 and on unix cpd /xw to set the plot device to X.
The color table is selected automatically. It can be changed using the cct command. A number of alternate color tables are available and these can be stepped through using cct/loop. For devices with limited colors or without image display capability a contour plot can be made with the contour command. The image should be smoothed beforehand using the smooth command.
saoimage can also be used to display an image. This is useful for panning and zooming of the image. The display is handled by writing an intermediate file. SAOIMAGE is run simply by typing saoimage at the ximage command line. It is not possible, however, to overlay grids and other items on the image.
Images can be placed side by side for comparison purposes using disp/left and disp/right/overlay. The currently active window is the last one displayed.
read/fits im1.fits ! read the 1st image display/left ! display the 1st image grid ! overlay the sky grid read/fits im2.fits ! read the 2nd image disp/right/overlay ! display the two side by side grid ! overlay the sky grid
The exact position and size of the image on the screen can be controlled using the /v qualifiers with the disp command. This is best done as part of a script .xco file, since it usually takes several attempts to get things right. Here is an example of plotting six images in four adjacent panels, with each label specified individually:
read/fits/size=64/xpix=440/ypix=410 s0_noflare2.img title " " title/low " " smooth/sig=0.8 DISP/V1=0.1/V2=0.4/V3=0.1/V4=0.4/no/log info/xs=15/scale=0.75 "Quiescent (smoothed)" read/fits/size=64/xpix=440/ypix=410 s0_yygem_flare.img title " " title/low "25/26 Oct 1993 ASCA SIS0" smooth/sig=0.8 DISP/V1=0.317/V2=0.617/V3=0.4/V4=0.7/overlay/no/log/scale=0.9 info/xs=15/scale=0.75 "YY Gem flare (smoothed)" read/fits/size=64/xpix=440/ypix=410 s0_castor_flare.img title " " title/low " YY Gem and Castor " smooth/sig=0.8 disp/v1=0.1/v2=0.4/v3=0.4/v4=0.7/overlay/scale=0.9/no/log info/xs=15/scale=0.75 "Castor Flare (smoothed)" read/fits/size=64/xpix=440/ypix=410 s0_noflare2.img title " " title/low " " disp/v1=0.317/v2=0.617/v3=0.1/v4=0.4/overlay/no/log info/xs=15/scale=0.75 "Quiescent"
Current and saved arrays are available to read in an exposure map. An exposure map contains as each element the total number of seconds that each pixel was exposed. Once an exposure map has been read in, then it is assumed that the vignetting correction has been applied to the map. If it has not, then the vignetting command can be used to apply the correction (for a known instrument).
The read/exposure command will read in an exposure map that is in FITS format. The exposure map must be read in after the corresponding image has been read, and it must have the same binning and size as that image. The map can be displayed using the disp/exp command. The exposure corrected image is displayed using disp/correct.
These are currently only supported for the EXOSAT CMA. In a future release it will be possible to read in a FITS image containing the background map.
XIMAGE keeps two images in its volatile memory. These are called the ``current image" and the ``saved image". The current image can be saved using command save_image and the saved image can be copied onto the current image with command restore_image. The first image loaded by XIMAGE is automatically saved.
The write command allows images to be written out in a number of different formats including FITS. The current exposure map can also be written using the /exposure qualifier. The currently displayed image is written using the /disp qualifier.
The extract command is used to obtain a spectrum and/or a lightcurve for the selected region (the default takes the whole image). The spectra are in the ASCII dump of the XSPEC sf format. The XSPEC mkpha program is used to convert it to XSPEC sf format. The lightcurve is an ASCII file in QDP format. It can be plotted using either QDP, or XRONOS. In the near future this will be changed so that the output is FITS files.