Free webp to jpg
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Image MIME Reference
PJPEG

Progressive JPEG (Legacy IE Alias)

image/pjpeg
VS

Valve Texture Format

image/vnd.valve.source.texture
VTF

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

PJPEG wins on browser support

Feature Support

Feature PJPEG VTF
Transparency (Alpha) ✕ No Yes
Animation Support ✕ No Yes
Progressive Loading Yes ✕ No
HDR Support ✕ No Yes
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 →
Valve Texture Format
image/vnd.valve.source.texture
Extension
.vtf
Container Valve Texture Format Header
Compression DXTC (DXT1, DXT3, DXT5) / Uncompressed (BGRA8888, RGB888, etc.)
Algorithm
DXT1-DXT5None
Color Depth 8-bit, 24-bit (RGB), 32-bit (RGBA), 16-bit Floating Point (HDR)
Developed by Valve Corporation
Released 2004
Magic Bytes
56 54 46 00
Full VTF reference →

Browser Support Comparison

Browser PJPEG VTF
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
VTF

VTF Strengths

  • Extremely fast loading within the Source Engine because the block-compressed data goes directly into the GPU's VRAM without CPU decompression overhead
  • Bundles mipmaps, volumetric slices, cubemap faces, and animation frames entirely within a single file
  • Openly documented by the Valve Developer Community, leading to a massive ecosystem of third-party modding tools
Limitations
  • Strictly tied to the Source Engine ecosystem; entirely useless in standard web or print contexts
  • No native support in standard image editors without hunting down and installing specialized plugins
  • Block compression algorithms (DXT) are lossy and can cause visible artifacting, especially on normal maps or smooth gradients

When to choose which format

PJPEG
Use PJPEG when…
  • Legacy Internet Explorer File Uploads
  • Progressive Image Rendering (Historical context)
VTF
Use VTF when…
  • Source Engine Game Textures
  • Custom Maps and Modding (Garry's Mod, CS:GO)
  • Animated In-Game Decals and Sprays
  • Environment Cubemaps (Skyboxes)

More comparisons

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