Some of the color map entries are reserved for such things as the colors of the screen or window background, the mouse cursor, and terminal window text, leaving fewer color map values for an application like SAOimage to use. See the color chapter for a more detailed discussion. The Image Data Image data may have an arbitrary range of data values. Data values may be very large or be very small or negative values, and they may have fractional components.
Image scaling involves binning groups of image data values for each display color map value.
Imagine that SAOimage has only 200 color map values to work with. Thus values 0 to 5 would be assigned the lowest color map slot, say 0. 6 to 11 would be assigned to 1, and so on up to the values between 1195 and 1199 going to slot 199 in the color map. Then, if slot 0 was black, all pixels in the image with data values between 0 and 5 would appear black in the display. If color map slot 131 was assigned the color pink, then image pixels whose data value was between 787 and 792 would appear pink in the display.