SGI (image file format)

File Format
Name	SGI (image file format)
Ontology	Electronic File Formats Graphics SGI (image file format)
Extension(s)	.sgi, .bw, .rgb, .rgba, others
PRONOM	x-fmt/140
Wikidata ID	Q7514956

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.

Format details

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 01 DA.

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
• Deark

Sample files

• RGB.tar.Z
• dexvert samples — image/sgi

Links

• Wikipedia article
• SGI Image File Format File Format Summary, from the Encyclopedia of Graphics File Formats