SGI-RGB

Silicon Graphics Image

image/x-rgb Released 1988 · by Silicon Graphics, Inc. (Paul Haeberli)

The image/x-rgb MIME type represents the Silicon Graphics Image (SGI) format, frequently referred to as the RGB format. Developed by Paul Haeberli at Silicon Graphics, Inc. (SGI) in the late 1980s for the IRIX workstation operating system, this raster format became an industry standard for high-end 3D rendering, animation, and visual effects software during the 1990s (such as Alias PowerAnimator and early versions of Maya). The format supports anywhere from 1 to 4 color channels (Grayscale, Grayscale+Alpha, RGB, RGBA) at 8 or 16 bits per channel, and can store pixels either completely uncompressed or using a highly efficient, scanline-based Run-Length Encoding (RLE) algorithm.

Legacy & Raster Graphics Transparency Production Ready

Technical Specifications

MIME Type

image/x-rgb

Extensions

.rgb.sgi.rgba.bw.int.inta

Container

SGI Image Header (512 bytes)

Compression

Uncompressed & Run-Length Encoding (RLE)

Algorithms

NoneScanline RLE

Color Depth

8-bit (Per Channel), 16-bit (Per Channel)

Metadata

None

Capabilities

Transparency

Animation

Progressive Loading

Alpha Channel

HDR Support

Official Specification

Aliases: image/rgbimage/x-sgiimage/sgi

Magic Bytes & HTTP Headers

File Signature (Magic Bytes)

01 DA

ASCII: \x01\xDA

HTTP Headers

Content-Type: image/x-rgb

Content-Type: image/x-sgi

HTML Accept Attribute

accept="image/x-rgb, .rgb, .sgi, .rgba, .bw"

Browser Support Matrix

Browser	Status	Min Version
Chrome	Not Supported	—
Firefox	Not Supported	—
Safari	Not Supported	—
Edge	Not Supported	—
Internet Explorer	Not Supported	Legacy

Advantages & Limitations

Advantages

Supports 16-bit precision per channel and an embedded alpha channel, making it ideal for the demanding compositing workflows of 1990s cinema VFX
The scanline-based RLE compression was exceptionally fast to decode on classic MIPS-based SGI workstations
Features a straightforward 512-byte header, making it relatively easy to parse and write custom decoders in C or Python

Limitations

Completely obsolete and unsupported in modern web environments
Replaced entirely by TIFF, OpenEXR, and PNG in modern visual effects and 3D rendering pipelines
Lacks support for modern color management via ICC profiles or advanced EXIF metadata

Developer Code Snippets

import magic
# Libmagic can easily detect the SGI magic bytes
print(magic.from_file('texture.sgi', mime=True)) # Outputs 'image/x-rgb' or 'image/x-sgi'

const fs = require('fs');
// Manually detecting the SGI magic header (0x01DA)
const buffer = Buffer.alloc(2);
const fd = fs.openSync('texture.rgb', 'r');
fs.readSync(fd, buffer, 0, 2, 0);
fs.closeSync(fd);
const isSGI = buffer[0] === 0x01 && buffer[1] === 0xDA;
console.log('Is Silicon Graphics RGB Image:', isSGI);

import (
    "bytes"
    "net/http"
)
// Native Go HTTP detection does not recognize SGI RGB.
// You must explicitly check the first two bytes:
// isSGI := len(buf) >= 2 && buf[0] == 0x01 && buf[1] == 0xDA

$mime = mime_content_type('texture.rgb');
echo $mime; // Standard PHP setups will return 'image/x-rgb' depending on the system magic database

File Detection Steps

How to programmatically detect a image/x-rgb file by reading its raw bytes:

1 Every valid SGI image file begins with a 2-byte 'magic number'. Check the first 2 bytes for the value 474 (Decimal), which translates to the bytes 0x01 and 0xDA in Hexadecimal.
2 Byte 2 (Offset 2) indicates the storage format: 0 means verbatim (uncompressed) and 1 means RLE compressed.
3 Byte 3 (Offset 3) indicates the Bytes Per Pixel Channel (BPC), which is almost universally 1 or 2 (representing 8-bit or 16-bit color precision).
4 Be extremely cautious of the .rgb extension on older FTP servers, as it was sometimes misused for raw interleaved pixel dumps lacking the 512-byte SGI header entirely.

Software Support

ImageMagick

GIMP

X

XnView

F

FFmpeg

Conversion Tools

Share & Embed

Markdown Badge

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Interactive iframe Widget

<iframe src="https://freewebptojpg.com/mime/image/sgi-rgb/embed" width="100%" height="280" style="border:1px solid #cbd5e1;border-radius:8px;" title="SGI-RGB Specs"></iframe>

JSON API

All data on this page is available as a free, open JSON API. Use it in your project, documentation, or tooling.

GET https://freewebptojpg.com/mime/image/sgi-rgb.json Open JSON

Free to use

No auth required

CORS enabled

Use from any domain

Cached 24h

Cache-Control headers set

Frequently Asked Questions

What is an SGI RGB file?

An SGI or RGB file is a legacy raster image format created by Silicon Graphics. It was heavily used in the 1990s by professional 3D animation, CAD, and visual effects software to store rendered frames and textures.

What is the difference between .sgi, .rgb, and .bw files?

They represent exactly the same file format. The different extensions were historically used as a naming convention by Unix users to indicate the number of color channels inside the file without having to parse the header: .bw for 1-channel grayscale, .rgb for 3-channel color, and .rgba for 4-channel color with transparency.

How can I view an image/x-rgb file?

Modern web browsers and most default operating system image viewers do not support the SGI format natively. You must use image editing software like GIMP, ImageMagick, or XnView to open them or convert them to modern formats like PNG or JPEG.