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Image MIME Reference
AVCS

AVC Image Sequence (HEIF Container)

image/avcs
VS

Windows Bitmap (Legacy Windows MIME Alias)

image/x-windows-bmp
BMP

A complete technical comparison of AVC Image Sequence (HEIF Container) and Windows Bitmap (Legacy Windows MIME Alias) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

BMP wins on browser support

Feature Support

Feature AVCS BMP
Transparency (Alpha) Yes Yes
Animation Support Yes ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes Yes
AVC Image Sequence (HEIF Container)
image/avcs
Extension
.avcs.heifs
Container HEIF / ISOBMFF (ISO/IEC 14496-12)
Compression Lossy / Lossless
Algorithm
AVC (Advanced Video Coding / H.264)
Color Depth 8-bit, 10-bit, 12-bit
Developed by Moving Picture Experts Group (MPEG) / ISO/IEC JTC 1
Released 2015
Magic Bytes
XX XX XX XX 66 74 79 70 61 76 63 73
Full AVCS reference →
Windows Bitmap (Legacy Windows MIME Alias)
image/x-windows-bmp
Extension
.bmp.dib
Container DIB (Device-Independent Bitmap)
Compression Uncompressed / Run-Length Encoding (RLE)
Algorithm
NoneRLE4RLE8
Color Depth 1-bit (Monochrome), 4-bit (16 colors), 8-bit (256 colors), 16-bit (High Color), 24-bit (True Color), 32-bit (True Color with Alpha)
Developed by Microsoft Corporation
Released 1985
Magic Bytes
42 4D
Full BMP reference →

Browser Support Comparison

Browser AVCS BMP
Chrome Chrome
✕
✓ 1
Firefox Firefox
✕
✓ 1
Safari Safari
✕
✓ 1
Edge Edge
✕
✓ 12
IE IE (Legacy)
✕
✓
AVCS

AVCS Strengths

  • Efficiently stores bursts of images or animations utilizing inter-frame compression
  • Leverages the highly compatible and widely hardware-accelerated AVC (H.264) codec
  • Robust HEIF container supports extensive metadata, alpha channels, and depth maps
Limitations
  • Zero native support in web browsers
  • Largely superseded in efficiency by newer sequence formats like HEICS (HEVC) or Animated AVIF (AV1)
  • Complicated container structure requires specialized parsing libraries
BMP

BMP Strengths

  • Universally supported by all major operating systems and modern web browsers
  • Maintains perfect, lossless fidelity because pixel data is stored without lossy compression artifacts
Limitations
  • Massive file size overhead due to a lack of modern compression algorithms
  • Legacy MIME strings like 'image/x-windows-bmp' can trigger validation warnings in strict security or API environments if unhandled

When to choose which format

AVCS
Use AVCS when…
  • Burst Photography
  • Short Animations
  • Camera Capture
  • Archival Storage
BMP
Use BMP when…
  • Legacy Windows Desktop Registry Associations
  • Older Enterprise Intranet Applications
  • Windows Graphics Archival

More comparisons

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