I realize IRAS-C supports images with a .CRL extension. Could you tell me what a CRL file is? What does CRL stand for? Is it a ZIImaging proprietary format?
CRL == Color Run Length.
Typically, run length encoded (RLE) data is binary, or single bit pixels. The COLOR run length format is for 8 or 16 bit pixels, possibly in combination with a color table -- but it uses run length compression. This is an Intergraph format, type 10 file. The format has been published, but there is little support outside of INGR/ZI software.
This type of compression is typically not very effective with photography or satellite imagery (because there are very few "runs" of identical pixels) . However, it is effective for computer generated imagery, or imagery that has been zoomed up in preparation for printing/plotting. The map setter software that INGR sells (sold ?) used this format extensively for color separates and plot files.