Image MIME Reference
ICO
Windows Icon (Legacy MIME)
image/x-icon
VS
PaintShop Pro Image
image/x-paintshoppro
PaintShop-Pro-PSP
A complete technical comparison of Windows Icon (Legacy MIME) and PaintShop Pro Image — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
ICO wins on browser support
Feature Support
| Feature | ICO | PaintShop-Pro-PSP |
|---|---|---|
| Transparency (Alpha) | Yes | Yes |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | Yes |
| EXIF Metadata | ✕ No | Yes |
| ICC Color Profile | ✕ No | Yes |
Windows Icon (Legacy MIME)
image/x-icon
Extension
.ico
Container
ICO Directory Structure
Compression
Uncompressed (DIB/BMP) / Deflate (Embedded PNG)
Algorithm
NoneDeflate (via PNG)
Color Depth
1-bit, 4-bit, 8-bit, 24-bit (True Color), 32-bit (RGBA)
Developed by
Microsoft Corporation
Released
1985
Magic Bytes
00 00 01 00
PaintShop Pro Image
image/x-paintshoppro
Extension
.psp.pspimage.tub.pat
Container
PSP Chunk-based Format
Compression
Uncompressed / RLE (Run-Length Encoding) / LZ77
Algorithm
RLELZ77
Color Depth
8-bit (Indexed), 16-bit (Grayscale), 24-bit (RGB), 32-bit (RGBA), 48-bit (High Color)
Developed by
Jasc Software / Corel Corporation (Alludo)
Released
1990
Magic Bytes
7E 42 4B 00
Browser Support Comparison
| Browser | ICO | PaintShop-Pro-PSP |
|---|---|---|
Chrome
|
✓ 1
|
✕ |
Firefox
|
✓ 1
|
✕ |
Safari
|
✓ 1
|
✕ |
Edge
|
✓ 12
|
✕ |
IE (Legacy)
|
✓
|
✕ |
ICO
ICO Strengths
- Universally supported by every web browser in existence for website favicons
- Packs multiple resolutions into a single file, eliminating the need to serve different files for the taskbar vs. the desktop
- Modern support for embedded PNGs (since Windows Vista) allows for excellent 32-bit transparency (alpha channels) and drastically reduced file sizes
Limitations
- Internal file structure is convoluted due to decades of legacy cruft, such as the requirement for BMP data to lack a standard file header but double the height property for an archaic XOR/AND mask
- Larger file size compared to a single optimized PNG or SVG, as it literally stores the same image multiple times at different scales
- The MIME type landscape is highly fragmented (x-icon vs. vnd.microsoft.icon), causing occasional caching or strict-MIME validation errors on restrictive servers
PaintShop-Pro-PSP
PaintShop-Pro-PSP Strengths
- Provides robust, non-destructive editing capabilities with full support for vector layers, adjustment layers, and layer blend modes
- Historically offered a highly capable and affordable alternative to Adobe Photoshop's PSD format for Windows users
- Features proprietary support for 'Picture Tubes' (.tub), a unique brush technology that paints sequential or random raster objects along a path
Limitations
- Deeply proprietary format tied exclusively to the Corel/Alludo ecosystem
- Third-party software support (like GIMP or ImageMagick) is often limited to parsing older .psp files, frequently failing to render complex layers in modern .pspimage files
- No support in modern web browsers; must be exported to a flattened web format (JPEG/PNG) for online viewing
When to choose which format
ICO
Use ICO when…
- Website Favicons (favicon.ico)
- Windows Application Executable Icons (.exe)
- Desktop Shortcut Icons
PaintShop-Pro-PSP
Use PaintShop-Pro-PSP when…
- PaintShop Pro Multi-layer Project Archival
- Digital Art and Photo Retouching
- Picture Tubes (.tub) and Custom Patterns (.pat)