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Image MIME Reference
AVIF

AV1 Image File Format

image/avif
VS

Windows Bitmap (Legacy Windows MIME Alias)

image/x-windows-bmp
BMP

A complete technical comparison of AV1 Image File Format 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 AVIF 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
AV1 Image File Format
image/avif
Extension
.avif
Container HEIF / ISOBMFF
Compression AV1 Lossy / AV1 Lossless
Algorithm
AV1
Color Depth 8-bit, 10-bit, 12-bit
Developed by Alliance for Open Media (AOMedia)
Released 2019
Magic Bytes
XX XX XX XX 66 74 79 70 61 76 69 66
Full AVIF 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 AVIF BMP
Chrome Chrome
✓ 85+
✓ 1
Firefox Firefox
✓ 93+
✓ 1
Safari Safari
✓ 16+
✓ 1
Edge Edge
✓ 121+
✓ 12
IE IE (Legacy)
✕
✓
AVIF

AVIF Strengths

  • Best-in-class compression — typically 20–50% smaller than WebP at equivalent quality
  • Native HDR and wide color gamut (BT.2020) support
  • Supports 8, 10, and 12-bit color depth
Limitations
  • Encoding is highly CPU-intensive — significantly slower than JPEG or WebP
  • Requires Edge 121+ (not supported in earlier Edge versions)
  • Limited support in native desktop image viewers
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

AVIF
Use AVIF when…
  • Next-Gen Websites
  • HDR Photography
  • High-Quality Web Images
BMP
Use BMP when…
  • Legacy Windows Desktop Registry Associations
  • Older Enterprise Intranet Applications
  • Windows Graphics Archival

More comparisons

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