Image MIME Reference
APNG
Animated Portable Network Graphics
image/vnd.mozilla.apng
VS
Computer Graphics Metafile
image/cgm
CGM
A complete technical comparison of Animated Portable Network Graphics and Computer Graphics Metafile — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
APNG wins on browser support
Feature Support
| Feature | APNG | CGM |
|---|---|---|
| Transparency (Alpha) | Yes | Yes |
| Animation Support | Yes | ✕ No |
| Progressive Loading | Yes | ✕ No |
| HDR Support | ✕ No | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | Yes | Yes |
Animated Portable Network Graphics
image/vnd.mozilla.apng
Extension
.apng.png
Container
PNG Chunk Stream
Compression
Deflate (Lossless)
Algorithm
Deflate (zlib)
Color Depth
8-bit (Indexed), 24-bit (TrueColor), 32-bit (RGBA)
Developed by
Mozilla Corporation (Stuart Parmenter & Vladimir Vukićević)
Released
2004
Magic Bytes
89 50 4E 47 0D 0A 1A 0A
Computer Graphics Metafile
image/cgm
Extension
.cgm
Container
CGM
Compression
Uncompressed / Binary / Character / Clear Text
Algorithm
Deflate (in some WebCGM profiles)
Color Depth
8-bit, 16-bit, 24-bit, 32-bit
Developed by
ISO / IEC
Released
1987
Magic Bytes
00 20 (Binary) / 42 45 47 49 4E 20 4D 45 54 41 46 49 4C 45 (Clear Text)
Browser Support Comparison
| Browser | APNG | CGM |
|---|---|---|
Chrome
|
✓ 59
|
✕ |
Firefox
|
✓ 3
|
✕ |
Safari
|
✓ 8
|
✕ |
Edge
|
✓ 79
|
✕ |
IE (Legacy)
|
✕ | ✕ |
APNG
APNG Strengths
- Supports 8-bit alpha transparency, completely solving the ugly 'white halo' problem inherent to GIFs
- Gracefully degrades; viewers that do not support APNG will render a perfectly valid, static PNG of the first frame
- Provides lossless compression that retains absolute pixel-perfect quality for UI elements and line art
Limitations
- Because it relies on lossless Deflate compression, file sizes for complex, video-like animations can be massive compared to lossy formats like WebP or AVIF
- Was initially rejected by the official PNG group, delaying its adoption for nearly a decade
- Lacks native hardware decoding acceleration, unlike video-based animated formats (like MP4 or WebM)
CGM
CGM Strengths
- Strictly standardized by ISO, ensuring long-term archiving and cross-platform compatibility in engineering
- Excellent support for rich metadata, hyperlinks, and technical hotspots via the WebCGM profile
- Can store complex 2D geometry, rasters, and text in a single lightweight file
Limitations
- Multiple encoding schemes (Binary, Character, Clear Text) make parser development difficult
- Zero native support in modern web browsers without third-party plugins
- Largely replaced by SVG for general-purpose 2D vector graphics on the web
When to choose which format
APNG
Use APNG when…
- High-Quality Web Animations
- Stickers (Apple iMessage, LINE, Discord)
- UI Loaders with Alpha Transparency
- GIF Replacement
CGM
Use CGM when…
- Technical Illustrations
- Aerospace & Defense (S1000D)
- CAD/CAM
- Geophysics