SGI (image file format)

SGI image (also known as IRIS, and sometimes called RGB or Irix RGB) is a raster image file format. It is associated with an image library used on Silicon Graphics workstations. The image may be uncompressed, or use RLE compression.

File structure
SGI image files start with a 512-byte fixed header, most of which is unused. If the image is uncompressed, the pixel data follows. Compressed images have a scan-line table, followed by the compressed pixel data.

The pixel data is stored bottom-up.

Image types
The following image types are supported:
 * Grayscale, 8 or 16 bits/sample
 * RGB, 8 or 16 bits/sample
 * RGBA, 8 or 16 bits/sample
 * RGB 3-3-2, 8 bits/pixel (obsolete)
 * Colormapped (but no palette is stored in the file) (obsolete)
 * Colormap (file contains only a palette; no image) (obsolete)
 * Grayscale+alpha images also exist, though they're not covered in the specification.

Identification
Files begin with bytes.

Specifications

 * The SGI Image File Format, Draft version 0.97: ftp.sgi.com archive → sgi/graphics/SGIIMAGESPEC
 * The SGI Image File Format, Version 1.00
 * Another copy: ftp.sgi.com_June2018 → ftp.sgi.com/sgi/graphics/grafica/sgiimage.html
 * SGI RGB Image Format

Software

 * Konvertor
 * Netpbm: pnmtosgi, sgitopnm
 * ImageMagick (format named "SGI")
 * Tom's Viewer
 * libimage

Sample files

 * RGB.tar.Z
 * https://telparia.com/fileFormatSamples/image/sgi/

Links

 * Wikipedia article
 * , from the Encyclopedia of Graphics File Formats