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Image MIME Reference
ACES

ACES Image Container File

image/aces
VS

Alias PIX Image

image/x-alias-pix
Alias-PIX

A complete technical comparison of ACES Image Container File and Alias PIX Image — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature ACES Alias-PIX
Transparency (Alpha) Yes ✕ No
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 →
Alias PIX Image
image/x-alias-pix
Extension
.pix.als.alias.img
Container Alias PIX Header
Compression Run-Length Encoding (RLE)
Algorithm
RLE
Color Depth 24-bit (RGB), 8-bit (Matte/Grayscale variant)
Developed by Alias Research (Later Alias|Wavefront / Autodesk)
Released Early 1990s
Magic Bytes
No explicit magic bytes (Relies on 10-byte integer header)
Full Alias-PIX reference →

Browser Support Comparison

Browser ACES Alias-PIX
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
Alias-PIX

Alias-PIX Strengths

  • The highly simplified structure made it incredibly fast to encode and decode on early 1990s SGI hardware
  • Lossless Run-Length Encoding (RLE) saved disk space without degrading the quality of final 3D renders
Limitations
  • Completely obsolete, having been replaced by more robust formats like TIFF, TGA, and EXR in modern 3D pipelines
  • The lack of a distinct magic byte signature makes reliable automated file detection almost impossible
  • Does not support integrated alpha channels, instead requiring cumbersome, separate 'Matte' files to denote transparency

When to choose which format

ACES
Use ACES when…
  • Visual Effects (VFX)
  • Digital Intermediate (DI)
  • Color Grading
  • Archival
Alias-PIX
Use Alias-PIX when…
  • Legacy Alias PowerAnimator Textures
  • 1990s SGI Workstation Render Outputs
  • Historical 3D Graphics Archival

More comparisons

ACES vs APNG → Alias-PIX vs APNG → ACES vs AVCI → Alias-PIX vs AVCI → ACES vs AVCS → Alias-PIX vs AVCS → ACES vs AVIF → Alias-PIX vs AVIF → All comparisons →
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