SGI to PGM Converter

SGI is the generic file extension for the Silicon Graphics Image format, also referred to by channel-specific extensions .rgb (3 channels), .rgba (4 channels), .bw (grayscale), and .int/.inta (16-bit variants). Developed by Silicon Graphics around 1986 for their IRIX operating system, the SGI format uses a 512-byte header followed by planar image data, where each color channel is stored as a complete plane rather than interleaved with other channels at each pixel. The header specifies a magic number (474), compression mode (0 for verbatim, 1 for RLE), bytes per channel (1 or 2), dimensionality (1 for scanline, 2 for image, 3 for multi-channel image), channel dimensions, pixel value range, and an 80-character image name. For RLE-compressed images, a table of offsets and lengths follows the header, allowing random access to individual scanlines without sequential decompression. Silicon Graphics workstations were the backbone of Hollywood visual effects, scientific visualization, flight simulation, and CAD/CAM industries throughout the 1990s, and the SGI format was the standard working format across these domains. One advantage is the format's robust design: the combination of scanline-addressable RLE compression, multi-channel support, 16-bit depth capability, and planar layout made it equally suitable for quick preview display and production rendering output. The format's association with the golden age of SGI-powered visual effects is another notable aspect — SGI files from this era represent production assets from landmark films and scientific visualizations. SGI images are supported by ImageMagick, GIMP, XnView, Photoshop (via plugin), and various 3D rendering and compositing applications.