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Image MIME Reference
ACES

ACES Image Container File

image/aces
VS

X Window Dump (Legacy MIME Alias)

image/x-xwindowdump
XWD

A complete technical comparison of ACES Image Container File and X Window Dump (Legacy MIME Alias) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature ACES XWD
Transparency (Alpha) Yes Yes
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
ACES Image Container File
image/aces
Extension
.exr
Container OpenEXR (SMPTE ST 2065-4)
Compression Lossless / Uncompressed
Algorithm
PIZZIPRLEB44Uncompressed
Color Depth 16-bit (Half-float), 32-bit (Float)
Developed by Academy of Motion Picture Arts and Sciences (AMPAS) / SMPTE
Released 2013
Magic Bytes
76 2F 31 01
Full ACES reference →
X Window Dump (Legacy MIME Alias)
image/x-xwindowdump
Extension
.xwd.wd
Container XWDHeader / XWDFileHeader Structure
Compression Uncompressed
Algorithm
None
Color Depth 8-bit (Indexed), 16-bit (High Color), 24-bit (True Color), 32-bit (True Color with Alpha/Padding)
Developed by MIT / X Consortium (X Window System)
Released 1987
Magic Bytes
00 00 00 64 (Typically indicates a 100-byte header size followed by version)
Full XWD reference →

Browser Support Comparison

Browser ACES XWD
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
ACES

ACES Strengths

  • Industry standard for high-end visual effects, compositing, and color grading
  • Supports 16-bit half-float data, accurately capturing immense dynamic range without clipping
  • Standardized by SMPTE (ST 2065-4) to guarantee universal color interoperability across different post-production facilities
Limitations
  • Considerably larger file sizes than conventional consumer image formats
  • Completely unsupported in web browsers and most standard desktop viewers
  • Requires specialized compositing or color grading software to interpret and view the scene-linear data correctly
XWD

XWD Strengths

  • Provides an exact, raw pixel dump directly from the X11 display server memory without compression overhead
  • Extremely fast for Unix environments to generate during low-level graphical debugging
Limitations
  • Completely uncompressed, resulting in large, bloated file sizes
  • Zero support in web browsers or modern desktop environments without specialized graphics translation tools
  • Verbose legacy MIME strings like 'image/x-xwindowdump' require backend normalization in modern applications

When to choose which format

ACES
Use ACES when…
  • Visual Effects (VFX)
  • Digital Intermediate (DI)
  • Color Grading
  • Archival
XWD
Use XWD when…
  • X Window System (X11) Display Debugging and Screenshots
  • Legacy Unix/Linux System Administration

More comparisons

ACES vs APNG → XWD vs APNG → ACES vs AVCI → XWD vs AVCI → ACES vs AVCS → XWD vs AVCS → ACES vs AVIF → XWD vs AVIF → All comparisons →
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