Image MIME Reference
HEIC
High Efficiency Image Container
image/heic
VS
PiCture eXchange
image/x-pcx
PCX
A complete technical comparison of High Efficiency Image Container and PiCture eXchange — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
HEIC wins on browser support
Feature Support
| Feature | HEIC | PCX |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | Yes | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | Yes | ✕ No |
| ICC Color Profile | Yes | ✕ No |
High Efficiency Image Container
image/heic
Extension
.heic
Container
HEIF / ISOBMFF
Compression
Lossy / Lossless
Algorithm
HEVC (H.265)
Color Depth
8-bit, 10-bit, 12-bit, 16-bit
Developed by
MPEG (Standard) / Apple (Adoption)
Released
2017
Magic Bytes
XX XX XX XX 66 74 79 70 68 65 69 63
PiCture eXchange
image/x-pcx
Extension
.pcx
Container
ZSoft Proprietary Header (128 bytes)
Compression
Run-Length Encoding (RLE)
Algorithm
ZSoft RLE
Color Depth
1-bit (Monochrome), 4-bit (16 colors), 8-bit (256 colors), 24-bit (True Color)
Developed by
ZSoft Corporation
Released
1985
Magic Bytes
0A (followed by version, e.g., 0A 05 01 08)
Browser Support Comparison
| Browser | HEIC | PCX |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✓ 11+
|
✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
HEIC
HEIC Strengths
- Exceptional compression efficiency — stores images at roughly half the file size of JPEG with equal or better visual quality
- Natively supports modern photography features like depth maps, 16-bit color, HDR, and alpha channel transparency
- Can store image bursts, focal stacks, and animations (Live Photos) within a single file
Limitations
- Heavily encumbered by software patents, leading to very poor adoption outside the Apple ecosystem
- Not supported by standard web browsers (except Safari), requiring server-side or client-side conversion for web delivery
- Windows requires downloading a separate (often paid) extension from the Microsoft Store to view natively
PCX
PCX Strengths
- Incredibly simple RLE algorithm makes it very fast to decode, which was historically vital for early 3D video game engines
- Retains crisp, lossless pixel data suitable for pixel art and interface assets
- Well-documented and highly supported by older desktop publishing and image editing software
Limitations
- Extremely inefficient compression by modern standards, producing large file sizes compared to PNG
- Lacks modern imaging features such as alpha channel transparency, EXIF metadata, and color profiles
- Zero support in web browsers; must be converted to PNG for web use
When to choose which format
HEIC
Use HEIC when…
- iOS / iPhone Photography
- macOS Ecosystem
- High-Quality Image Archiving
PCX
Use PCX when…
- MS-DOS and Early Windows Graphics
- 1990s Video Game Assets (Textures, UI)
- Retro Computing Archival