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Image MIME Reference
AVCI

AVC Image (HEIF Container)

image/avci
VS

X Window Dump (Legacy MIME Alias)

image/x-xwindowdump
XWD

A complete technical comparison of AVC Image (HEIF Container) 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 AVCI XWD
Transparency (Alpha) Yes Yes
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
AVC Image (HEIF Container)
image/avci
Extension
.avci.hif
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 69
Full AVCI 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 AVCI XWD
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
AVCI

AVCI Strengths

  • Shares the robust, flexible HEIF container architecture that allows for rich metadata, HDR, and depth maps.
  • Backed by the highly ubiquitous AVC (H.264) codec, which is widely supported in hardware decoding.
  • Supports rectangular cropping and rotation metadata without needing to re-encode the pixel data.
Limitations
  • No native support within web browsers for HTML rendering.
  • Inferior compression efficiency when compared to newer container formats like HEIC (HEVC) or AVIF (AV1).
  • Easily confused with HEIC and AVIF, which use the same base ISOBMFF container.
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

AVCI
Use AVCI when…
  • Digital Photography
  • Camera Capture
  • Archival Storage
XWD
Use XWD when…
  • X Window System (X11) Display Debugging and Screenshots
  • Legacy Unix/Linux System Administration

More comparisons

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