Image MIME Reference
DPX
Digital Picture Exchange
image/dpx
VS
Portable Bitmap
image/x-portable-bitmap
PBM
A complete technical comparison of Digital Picture Exchange and Portable Bitmap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | DPX | PBM |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | ✕ No | ✕ No |
Digital Picture Exchange
image/dpx
Extension
.dpx
Container
DPX (SMPTE ST 268)
Compression
Uncompressed / RLE (Rarely used)
Algorithm
Uncompressed
Color Depth
8-bit, 10-bit, 12-bit, 16-bit, 32-bit (Float)
Developed by
SMPTE (Society of Motion Picture and Television Engineers)
Released
1994
Magic Bytes
53 44 50 58 (Big-endian) / 58 50 44 53 (Little-endian)
Portable Bitmap
image/x-portable-bitmap
Extension
.pbm
Container
Netpbm
Compression
Uncompressed
Algorithm
None
Color Depth
1-bit (Monochrome)
Developed by
Jef Poskanzer (Netpbm Project)
Released
1988
Magic Bytes
50 31 (ASCII) or 50 34 (Binary)
Browser Support Comparison
| Browser | DPX | PBM |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
DPX
DPX Strengths
- Industry standard for transferring uncompressed, high-fidelity film and VFX data
- Rich industry-specific metadata including timecode, keykode, and film stock information
- Supports logarithmic color spaces (LogC, Cineon) to preserve the massive dynamic range of film negatives
Limitations
- Massive file sizes (e.g., a single 4K 10-bit frame is ~50MB, resulting in ~1.2GB per second at 24fps)
- Zero native support in web browsers or consumer OS image viewers
- Requires heavy-duty, fast storage infrastructure (RAID/NVMe) to playback in real-time
PBM
PBM Strengths
- Absolute structural simplicity allows parsers to be written from scratch with just a few lines of code
- ASCII encoding allows manual editing and debugging directly within a standard text editor
- Serves as a flawless, lossless intermediary for 1-bit raster data like scanned documents or barcodes
Limitations
- Strictly limited to 1-bit monochrome images; cannot natively display shades of gray or color
- Lack of compression results in extremely large file sizes, particularly when using the ASCII 'P1' encoding
- No support for alpha transparency or modern metadata standards like EXIF
When to choose which format
DPX
Use DPX when…
- Film Scanning
- Visual Effects (VFX)
- Digital Intermediate (DI)
- Color Grading
- Archival
PBM
Use PBM when…
- Optical Character Recognition (OCR) Pre-processing
- Unix/Linux Command-Line Image Pipelines
- Academic Image Processing Teaching