GIMP can both read and write to the SGI file format. This format, by Silicon Graphics Inc., supports black and white (usually with the extension .bw), color (.rgb), and color images with an alpha channel (.rgba). You may also find SGI files in any of the above formats with the extension .sgi. SGI images are normally only found on SGI workstations.
When saving an SGI image, GIMP will prompt you to specify a compression type. RLE (Run Length Encoded) compression is recommended because it is a lossless format. The Aggressive RLE option may produce a smaller file size, but SGI applications may not open the image correctly.