Advanced use of `image'

Now consider this more complex sequence of commands.

   % xdisplay abc.inter.net
   % xmake xwindows -g 400x300 -c 128

   ICL> image image=a_file prompt
   HARDCOPY - Use "hard" devices rather than imaging device /FALSE/ >
   IDEV /'xw'/ >
   ERASE - Erase screen before display /FALSE/ > t
   YSTART - First Y value to be displayed /1/ > min
   YEND - Last Y value to be displayed /256/ > max
   XSTART - First X value to be displayed /1/ > min
   XEND - Last X value to be displayed /256/ > max
   LOG - Display using logarithmic scaling /FALSE/ >
   OPTIMIZE - Amount of histogram optimisation (0 to 1) /0.5/ > 0
   AUTOSCALE - Calculate display limits automatically /TRUE/ >
   NEGATIVE - Set limits to give a negative image /FALSE/ > t
   XPLACES - Number of sub-displays across screen in X /1/ >
   YPLACES - Number of sub-displays across screen in Y /1/ >
   ASPECT - Maintain correct aspect ratio for image? /TRUE/ >
   IMARRAY /0/ >
   IMFILE /''/ >

   ICL> image a_file negative=t
   ERASE - Erase screen before display /FALSE/ >
   YSTART - First Y value to be displayed /1/ > 173
   YEND - Last Y value to be displayed /256/ > 191
   XSTART - First X value to be displayed /1/ > 94
   XEND - Last X value to be displayed /256/ > 117
   OPTIMIZE - Amount of histogram optimisation (0 to 1) /0/ >
   AUTOSCALE - Calculate display limits automatically /TRUE/ >
   XPLACES - Number of sub-displays across screen in X /1/ > 0
   XORIGIN - Origin of display in X in display pixels /0/ > 250
   YORIGIN - Origin of display in Y in display pixels /0/ > 150
   XPIXELS - Number of display pixels to use in X /149/ >
   YPIXELS - Number of display pixels to use in X /149/ >
   ASPECT - Maintain correct aspect ratio for image? /TRUE/ >

If you are not familiar with the necessities of using X windows over the computer network, see the section on plotting a spectrum.

In the first `image' command the keyword `prompt' is used. While `accept' suppresses prompting as far as possible, `prompt' causes any command to ask you everything. This is a good way of learning the capabilities of commands, but it also causes some spurious prompts like the ones for `idev', `imarray', and `imfile'. You should just accept the defaults offered for these parameters.

The first thing we learn through the `prompt' keyword is that `image' could have `displayed' to a printer file instead of a screen window.

We chose to erase the window this time. That gets rid of the remainders of the original plain box. Via `ystart'/`yend' and `xstart'/`xend' we can select only part of the image to be displayed. Since we want the whole image and are not sure about the offered default, we use the words `min' and `max'. This time, we set `negative' true: The image file contains a negative, negating it during display makes is look positive. With `xplaces'/`yplaces' we could sub-divide the window into an array of sub-windows and display into one of them. We leave `aspect' true so that image pixels are displayed as squares. Otherwise the display would be stretched horizontally to fill the window.

Having displayed the whole image, we now run `image' again, but display only part of it. We also set `xplaces' zero. That means, we can specify the display area in pixels. Since we do not erase this time, the previous full display remains partially visible.