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Image MIME Reference
BMP

Windows Bitmap (Legacy Windows MIME Alias)

image/x-windows-bmp
VS

JPEG 2000 Image Sequence (Obsolete)

image/hsj2
HSJ2

A complete technical comparison of Windows Bitmap (Legacy Windows MIME Alias) and JPEG 2000 Image Sequence (Obsolete) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

BMP wins on browser support

Feature Support

Feature BMP HSJ2
Transparency (Alpha) Yes Yes
Animation Support ✕ No Yes
Progressive Loading ✕ No Yes
HDR Support ✕ No Yes
EXIF Metadata ✕ No Yes
ICC Color Profile Yes Yes
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 →
JPEG 2000 Image Sequence (Obsolete)
image/hsj2
Extension
.hsj2
Container HEIF / ISOBMFF (ISO/IEC 15444-16 Obsolete)
Compression Lossy / Lossless
Algorithm
Motion JPEG 2000 (ISO/IEC 15444-3)
Color Depth 8-bit, 10-bit, 12-bit, 16-bit
Developed by ISO/IEC JTC 1 / ITU-T
Released 2019
Magic Bytes
XX XX XX XX 66 74 79 70 68 73 6A 32
Full HSJ2 reference →

Browser Support Comparison

Browser BMP HSJ2
Chrome Chrome
✓ 1
 ✕
Firefox Firefox
✓ 1
 ✕
Safari Safari
✓ 1
 ✕
Edge Edge
✓ 12
 ✕
IE IE (Legacy)
✓
 ✕
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
HSJ2

HSJ2 Strengths

  • Historically attempted to combine Motion JPEG 2000 sequences with the flexible metadata capabilities of the HEIF container
  • Supported mathematically lossless compression and scalable wavelet decoding
Limitations
  • Officially deprecated by the standardization body (ISO/IEC JTC 1)
  • Completely superseded by image/hej2k, rendering hsj2 files obsolete for any new development or archiving
  • Zero web browser compatibility and negligible modern software support

When to choose which format

BMP
Use BMP when…
  • Legacy Windows Desktop Registry Associations
  • Older Enterprise Intranet Applications
  • Windows Graphics Archival
HSJ2
Use HSJ2 when…
  • Legacy Archival
  • Deprecated Workflows

More comparisons

BMP vs ACES → HSJ2 vs ACES → BMP vs APNG → HSJ2 vs APNG → BMP vs AVCI → HSJ2 vs AVCI → BMP vs AVCS → HSJ2 vs AVCS → BMP vs AVIF → HSJ2 vs AVIF → All comparisons →
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