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Image MIME Reference
HEIF

High Efficiency Image File Format

image/heif
VS

X Window Dump (Legacy MIME Alias)

image/x-xwindowdump
XWD

A complete technical comparison of High Efficiency Image File Format 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 HEIF XWD
Transparency (Alpha) Yes Yes
Animation Support Yes ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
High Efficiency Image File Format
image/heif
Extension
.heif.hif
Container HEIF / ISOBMFF (ISO/IEC 14496-12)
Compression Lossy / Lossless
Algorithm
Codec Agnostic (HEVC, AVC, JPEG, AV1)
Color Depth 8-bit, 10-bit, 12-bit, 16-bit
Developed by Moving Picture Experts Group (MPEG)
Released 2015
Magic Bytes
XX XX XX XX 66 74 79 70 6D 69 66 31
Full HEIF 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 HEIF XWD
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
HEIF

HEIF Strengths

  • Highly flexible container that can store image bursts, animations, focal stacks, and stereo 3D images in one file
  • Natively supports depth maps and alpha channels, making it perfect for computational photography
  • When paired with modern codecs like HEVC or AV1, it provides massive storage savings over legacy formats like JPEG
Limitations
  • Codec agnosticism makes broad software decoding difficult, as the container might hold proprietary or unsupported codecs
  • Zero cross-platform web browser support, requiring conversion for online publishing
  • Often confused with the more specific 'image/heic' and 'image/avif' MIME types
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

HEIF
Use HEIF when…
  • Digital Photography
  • Camera Capture
  • Image Archiving
  • Multi-image composites
XWD
Use XWD when…
  • X Window System (X11) Display Debugging and Screenshots
  • Legacy Unix/Linux System Administration

More comparisons

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