Free webp to jpg
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Image MIME Reference
PJPEG

Progressive JPEG (Legacy IE Alias)

image/pjpeg
VS

Adobe Photoshop Document

image/vnd.adobe.photoshop
PSD

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

PJPEG wins on browser support

Feature Support

Feature PJPEG PSD
Transparency (Alpha) ✕ No Yes
Animation Support ✕ No Yes
Progressive Loading Yes ✕ No
HDR Support ✕ No Yes
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 →
Adobe Photoshop Document
image/vnd.adobe.photoshop
Extension
.psd.psb.pdd
Container Adobe Photoshop Document (PSD/PSB)
Compression Uncompressed / RLE (Run-Length Encoding) / ZIP
Algorithm
RLEZIP (with or without prediction)None
Color Depth 1-bit (Bitmap), 8-bit, 16-bit, 32-bit (Float/HDR)
Developed by Adobe Systems
Released 1990
Magic Bytes
38 42 50 53
Full PSD reference →

Browser Support Comparison

Browser PJPEG PSD
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
PSD

PSD Strengths

  • The undisputed global standard for layered raster graphics and non-destructive image editing
  • Supports incredibly complex compositions combining raster data, vector shapes, live text, and adjustment layers
  • Full support for advanced color spaces (CMYK, Lab, multi-channel) and 32-bit floating-point HDR workflows
Limitations
  • Proprietary format: while the specification is published, complete feature-parity is rarely achieved by third-party software (e.g., smart objects and complex layer styles often break)
  • Files can reach enormous sizes (gigabytes) due to the preservation of unflattened, high-resolution layer data
  • Zero support for native rendering in web browsers or standard mobile image viewers

When to choose which format

PJPEG
Use PJPEG when…
  • Legacy Internet Explorer File Uploads
  • Progressive Image Rendering (Historical context)
PSD
Use PSD when…
  • Professional Photo Retouching
  • Digital Painting and Illustration
  • UI/UX Design Workflows
  • Graphic Design and Print Production

More comparisons

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