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.SUN

SUN

Sun Raster (Sun Rasterfile / RAS)

Data type	Image
MIME type	image/x-sun-raster
Developer	Sun Microsystems
Primary use cases	Legacy SunOS/Solaris raster graphics; interchange/compatibility with older UNIX tooling; archived bitmap assets from Sun workstations

What is the SUN file format?

SUN (Sun Raster) is a legacy bitmap format from Sun Microsystems (SunOS/Solaris) with a simple header, optional palette, and pixel data stored uncompressed or with basic RLE.

SUN file characteristics

Data type	Image
MIME type	image/x-sun-raster
Compression	Optional lossless RLE
Color depth	Historically common depths are 1-bit (bitmap) and 8-bit (grayscale or paletted); many decoders also support 24-bit (color) and 32-bit (color with an extra byte used as padding/attributes rather than alpha)
Color space	Grayscale, indexed/paletted (with colormap), and RGB; some toolchains support 24/32-bit variants; transparency is not defined by the format
Transparency support	No
Animation support	No
EXIF / Metadata support	No
Metadata	Very limited. The header and optional colormap carry technical info; there is no standardized Exif/XMP container. Some software may store extra data via nonstandard conventions, but interoperability is not guaranteed.
Structure type	Header + optional colormap + pixel data (rows padded to 16-bit) with optional byte-RLE
Standard / Specification	SunOS rasterfile.h / rasterfile(5) (commonly referenced as rasterfile.h 1.11 dated 1989-08-21)
Typical file size	Often large because data is commonly uncompressed; RLE may reduce size for flat areas but not for photographic/noisy images
Year introduced	1989

Advantages

The SUN file format offers several advantages that make it suitable for common use cases.

Simple structure;
Lossless storage (raw or RLE);
Supports palette/grayscale/RGB;
Widely supported by conversion tools for legacy compatibility

Limitations

The SUN file format has certain limitations that may affect its use in specific scenarios.

Unofficial MIME types vary;
Many modern apps don’t open it natively. No standard transparency/alpha semantics, no layers, and limited metadata. Best used as a legacy interchange format—convert to PNG/WebP/AVIF for delivery.

Compatibility

SUN images are widely supported and can be viewed on most devices and platforms.

Supported platforms: Unix/Solaris heritage; today readable on Windows, macOS, Linux via tools/libraries (e.g., Netpbm, ImageMagick, GIMP, FFmpeg)
Supported devices: Legacy Unix workstations; modern computers via converters/viewers
Browser support: No
Mobile support: No
Backward compatibility: Yes

Security considerations

Treat as untrusted input: validate dimensions, row padding expectations, and RLE streams to avoid overflows/overreads in decoders

License

Legacy vendor format; specification is publicly documented (SunOS rasterfile.h / rasterfile(5)); not a formal modern standard

SUN usually refers to the Sun Raster (RAS) file format used on SunOS. Files commonly use the extensions .ras and .sun. The format starts with an 8×32-bit integer header (magic 0x59A66A95), followed by an optional color map, then raster lines stored top-to-bottom; each row is padded to a 16-bit boundary. Data may be uncompressed (RT_OLD/RT_STANDARD) or byte-RLE encoded (RT_BYTE_ENCODED). The format is publicly documented in Sun’s rasterfile.h / rasterfile(5), but it has no officially registered IANA MIME type—software often uses unofficial types like image/x-sun-raster or image/x-cmu-raster.