Free webp to jpg
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Image MIME Reference
PJPEG

Progressive JPEG (Legacy IE Alias)

image/pjpeg
VS

WebP Image

image/webp
WebP

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

Equal browser support

Feature Support

Feature PJPEG WebP
Transparency (Alpha) ✕ No Yes
Animation Support ✕ No Yes
Progressive Loading Yes ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata Yes Yes
ICC Color Profile Yes Yes
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 →
WebP Image
image/webp
Extension
.webp
Container RIFF
Compression Lossy / Lossless
Algorithm
VP8VP8L
Color Depth 8-bit
Developed by Google
Released 2010
Magic Bytes
52 49 46 46 XX XX XX XX 57 45 42 50
Full WebP reference →

Browser Support Comparison

Browser PJPEG WebP
Chrome Chrome
✓ All
✓ 32+
Firefox Firefox
✓ All
✓ 65+
Safari Safari
✓ All
✓ 14+
Edge Edge
✓ All
✓ 18+
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
WebP

WebP Strengths

  • Superior lossy compression — 25–35% smaller than JPEG at equivalent quality
  • Supports both animation and full alpha transparency
  • Lossless mode available with smaller file sizes than PNG
Limitations
  • Slower encoding than JPEG, especially for lossless
  • Not supported in Internet Explorer or very old browsers

When to choose which format

PJPEG
Use PJPEG when…
  • Legacy Internet Explorer File Uploads
  • Progressive Image Rendering (Historical context)
WebP
Use WebP when…
  • Websites
  • Ecommerce
  • Mobile Apps
  • CMS Images

More comparisons

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