Image MIME Reference
PWG-Raster
PWG Raster Format
image/pwg-raster
VS
RealNetworks RealPix
image/vnd.rn-realpix
RealPix
A complete technical comparison of PWG Raster Format and RealNetworks RealPix — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | PWG-Raster | RealPix |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | Yes |
| Progressive Loading | ✕ No | Yes |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | ✕ No | ✕ No |
PWG Raster Format
image/pwg-raster
Extension
.pwg.ras
Container
CUPS Raster v2 Container
Compression
PackBits (Run-Length Encoding)
Algorithm
PackBits (Apple RLE variant)
Color Depth
1-bit (Monochrome/K), 8-bit (Grayscale), 24-bit (sRGB / Adobe RGB), 32-bit (CMYK)
Developed by
IEEE-ISTO Printer Working Group (PWG)
Released
2011
Magic Bytes
52 61 53 32
RealNetworks RealPix
image/vnd.rn-realpix
Extension
.rp
Container
IMFL (XML Markup)
Compression
Uncompressed (Plain Text Markup)
Algorithm
None (Plain Text)
Color Depth
Dependent on referenced images
Developed by
RealNetworks
Released
1998
Magic Bytes
3C 69 6D 66 6C
Browser Support Comparison
| Browser | PWG-Raster | RealPix |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
PWG-Raster
PWG-Raster Strengths
- The undisputed global standard for modern, driverless printing environments, eliminating the nightmare of installing manufacturer-specific print drivers
- Extremely lightweight to decode on embedded hardware, requiring minimal RAM buffers on the printer side
- Strict color space and resolution rules guarantee that the printed output will successfully process without syntax errors
Limitations
- Generates massive file sizes and network payloads compared to vector-based formats like PDF or PostScript, as every page is fully rasterized at 300+ DPI before transmission
- No support for native rendering in web browsers, image viewers, or graphic design software without specialized CUPS developer tools
- Cannot store complex metadata, vector text, or layers
RealPix
RealPix Strengths
- Allowed for 'Ken Burns'-style animated slideshows at a fraction of the bandwidth required for actual video, crucial for 1990s dial-up connections
- Plain text XML architecture made it easy for developers and hobbyists to hand-code complex multimedia presentations
- Perfectly synchronized with RealAudio streams using SMIL-like timing parameters
Limitations
- Completely obsolete and heavily reliant on the proprietary, defunct RealPlayer browser plugin
- Not a true image format, causing confusion when handled by standard image processing libraries which expect binary pixel data
- Lacks modern CSS or HTML5 canvas equivalents without completely rewriting the presentation logic
When to choose which format
PWG-Raster
Use PWG-Raster when…
- Driverless Network Printing (IPP Everywhere)
- Apple AirPrint and Mopria Print Service Pipelines
- CUPS (Common UNIX Printing System) Spooling
RealPix
Use RealPix when…
- Historical Dial-up Streaming Presentations
- RealPlayer Slideshows
- Bandwidth-efficient 'Video' Alternatives (late 1990s)