Silicon Graphics Image

Silicon Graphics Image (SGI) or the RGB file format is the native raster graphics file format for Silicon Graphics workstations. The format was invented by Paul Haeberli. It can be run-length encoded (RLE). FFmpeg and ImageMagick, among others, support this format.

Background

Common file extensions are:

;.sgi or .rgb: 3 colour channels
; .rgba: 3 colour channels and alpha
;.bw or .int: black and white
;.inta: black and white and alpha

This format was originally developed for IRIX. The master files of the '' SVT High Definition Multi Format Test Set'' are SGIs. Frame 200 of the ''ParkJoy'' sequence in this set (15722.sgi, 3840×2160, 47.4 MB) was used in WebP comparisons.

Technical Details

SGI image format use big endian order. Image data scan from left to right from bottom to top.

Header

File Signature/Magic Number

Should equal 0x01 0xda for SGI file.

Compression

If no compression equal 0; 1 for RLE compression.

Bytes Per Pixel Channel

Value is 1 for 8 bit per channel (most image); 2 for 16 bits per channel.

Dimension

Value equal 1 for 1 channel, 1 scanline image ; 2 for 1 channel, many scanline image (); 3 for many channel, many scanline image (most image).

X Size

Scanline width of image.

Y Size

Number of scanlines in image.

Number Of Channels

Number channels in image. Grey scale image is 1; RGB is 3; RGBA is 4. SGI can have more than 4 channels.

Minimum Pixel Value

Smallest pixel value in all channels. Because SGI use unsigned char or short for channels, smallest value can have is zero.

Maximum pixel value

Largest pixel value in all channels. Because SGI use unsigned char or short for channels, largest value can have for 8 bit/channel is 0xff; 16 bit/channel image is 0xffff.

Dummy

4 bytes not use.

Image name

Image name is 80 bytes (maximum 79 characters ≠ 0x00) C string. If name is shorter than 79 characters, all bytes after equal 0x00 for fill all 80 bytes.

Color Map ID
Have 4 type