Image MIME Reference
Harlequin-PGB
Global Graphics Page Graphics Buffer
image/vnd.globalgraphics.pgb
VS
Portable Pixmap
image/x-portable-pixmap
PPM
A complete technical comparison of Global Graphics Page Graphics Buffer and Portable Pixmap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | Harlequin-PGB | PPM |
|---|---|---|
| Transparency (Alpha) | ✕ No | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | Yes |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | Yes | ✕ No |
Global Graphics Page Graphics Buffer
image/vnd.globalgraphics.pgb
Extension
.pgb
Container
Proprietary Harlequin Raster Container
Compression
Uncompressed / Run-Length Encoding (RLE)
Algorithm
Proprietary RLENone
Color Depth
1-bit (Monochrome Separations), 8-bit (Grayscale), 8-bit/10-bit (Contone), CMYK / N-Color Spot Channels
Developed by
Global Graphics Software (Hybrid Software Group)
Released
1990s
Magic Bytes
Unknown (Proprietary Harlequin Header)
Portable Pixmap
image/x-portable-pixmap
Extension
.ppm
Container
Netpbm
Compression
Uncompressed
Algorithm
None
Color Depth
24-bit (RGB), 48-bit (RGB High Color)
Developed by
Jef Poskanzer (Netpbm Project)
Released
1988
Magic Bytes
50 33 (ASCII) or 50 36 (Binary)
Browser Support Comparison
| Browser | Harlequin-PGB | PPM |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
Harlequin-PGB
Harlequin-PGB Strengths
- Unlike generic 1-bit TIFFs, PGB files inherently encapsulate vital print-job metadata within their headers (e.g., job name, page number, separation colors, screening angles)
- Highly optimized for ultra-fast viewing and processing within professional printing workflows
Limitations
- Completely proprietary and closed-source, locking its usage strictly to Harlequin-powered RIP environments
- Zero support in standard desktop operating systems, web browsers, or consumer image editing software like Photoshop or GIMP
PPM
PPM Strengths
- Absolute structural simplicity allows parsers and renderers (such as custom raytracers) to write directly to the format with virtually no overhead or external libraries
- Supports 16-bit per channel (48-bit total) precision, preserving deep color accuracy before converting to final delivery formats
- ASCII encoding ('P3') allows manual editing and visual inspection of RGB values directly within a text editor
Limitations
- Zero compression results in astronomical file sizes, making it entirely impractical for web delivery or consumer storage
- Does not natively support an alpha channel for transparency (this is handled by the newer PAM extension format within the Netpbm suite)
- Lacks support for modern metadata standards like EXIF, XMP, or embedded ICC color profiles
When to choose which format
Harlequin-PGB
Use Harlequin-PGB when…
- Commercial Printing Output
- Computer-to-Plate (CTP) Manufacturing
- Prepress Soft Proofing (e.g., FirstPROOF)
- Harlequin RIP Spooling Pipelines
PPM
Use PPM when…
- Intermediary Format for Image Format Conversion
- Academic Computer Graphics and Raytracing Output
- Unix/Linux Command-Line Image Pipelines