Free webp to jpg
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Image MIME Reference
PJPEG

Progressive JPEG (Legacy IE Alias)

image/pjpeg
VS

Wireless Bitmap

image/vnd.wap.wbmp
WBMP

A complete technical comparison of Progressive JPEG (Legacy IE Alias) and Wireless Bitmap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

PJPEG wins on browser support

Feature Support

Feature PJPEG WBMP
Transparency (Alpha) ✕ No ✕ No
Animation Support ✕ No ✕ No
Progressive Loading Yes ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
Progressive JPEG (Legacy IE Alias)
image/pjpeg
Extension
.jpeg.jpg.pjpeg.pjp.jfif
Container JPEG (ISO/IEC 10918-1)
Compression Lossy (DCT)
Algorithm
Discrete Cosine Transform (DCT)
Color Depth 8-bit, 12-bit
Developed by Joint Photographic Experts Group / Microsoft (Alias)
Released 1992
Magic Bytes
FF D8 FF E0 (JFIF) / FF D8 FF E1 (Exif)
Full PJPEG reference →
Wireless Bitmap
image/vnd.wap.wbmp
Extension
.wbmp
Container WBMP Type 0
Compression Uncompressed
Algorithm
None
Color Depth 1-bit (Monochrome)
Developed by WAP Forum (Now Open Mobile Alliance)
Released 1999
Magic Bytes
00 00
Full WBMP reference →

Browser Support Comparison

Browser PJPEG WBMP
Chrome Chrome
✓ All
 ✕
Firefox Firefox
✓ All
 ✕
Safari Safari
✓ All
 ✕
Edge Edge
✓ All
 ✕
IE IE (Legacy)
✓
 ✕
PJPEG

PJPEG Strengths

  • Progressive JPEGs (which this MIME type attempted to describe) provide excellent perceived loading speeds on slow connections by rendering a low-resolution preview first
  • Files sent with this MIME type are fully backwards compatible with any standard JPEG decoder
Limitations
  • It is a non-standard MIME type that violates IANA specifications
  • Causes strict file upload validation scripts to fail if not explicitly whitelisted or mapped
  • Creates unnecessary confusion, as the official image/jpeg MIME type already fully encompasses progressive encoding
WBMP

WBMP Strengths

  • Extremely low processing overhead made it perfectly suited for the ultra-low-power CPUs of late 1990s mobile devices
  • Tightly integrated into the WML (Wireless Markup Language) stack, enabling the first functional mobile internet experiences
Limitations
  • Completely obsolete and lacks support in modern operating systems and browsers
  • Limited entirely to 1-bit black and white (0 for black, 1 for white) with zero support for grayscale, color, or transparency
  • The lack of a strong file header signature makes automated MIME type detection highly unreliable

When to choose which format

PJPEG
Use PJPEG when…
  • Legacy Internet Explorer File Uploads
  • Progressive Image Rendering (Historical context)
WBMP
Use WBMP when…
  • Legacy WML (Wireless Markup Language) Mobile Sites
  • Early Mobile Phone Icons and Operator Logos
  • Historical WAP Archival

More comparisons

PJPEG vs ACES → WBMP vs ACES → PJPEG vs APNG → WBMP vs APNG → PJPEG vs AVCI → WBMP vs AVCI → PJPEG vs AVCS → WBMP vs AVCS → PJPEG vs AVIF → WBMP vs AVIF → All comparisons →
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