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Image MIME Reference
AVCI

AVC Image (HEIF Container)

image/avci
VS

Portable Graymap

image/x-portable-graymap
PGM

A complete technical comparison of AVC Image (HEIF Container) and Portable Graymap — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature AVCI PGM
Transparency (Alpha) Yes ✕ No
Animation Support ✕ No ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes Yes
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 →
Portable Graymap
image/x-portable-graymap
Extension
.pgm
Container Netpbm
Compression Uncompressed
Algorithm
None
Color Depth 8-bit (Grayscale), 16-bit (Grayscale)
Developed by Jef Poskanzer (Netpbm Project)
Released 1988
Magic Bytes
50 32 (ASCII) or 50 35 (Binary)
Full PGM reference →

Browser Support Comparison

Browser AVCI PGM
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.
PGM

PGM Strengths

  • Extremely simple format allows custom parsers to be written from scratch in minimal time
  • Supports 16-bit precision, making it highly valuable for scientific, medical, and height-map data where 8-bit precision is insufficient
  • ASCII encoding ('P2') allows manual editing and visual inspection of pixel values directly within a text editor
Limitations
  • Strictly limited to grayscale; cannot display color
  • Lack of compression results in massive file sizes, making it entirely impractical for web delivery or consumer storage
  • Does not support alpha transparency or modern metadata structures

When to choose which format

AVCI
Use AVCI when…
  • Digital Photography
  • Camera Capture
  • Archival Storage
PGM
Use PGM when…
  • Computer Vision and Machine Learning Pre-processing
  • Scientific and Medical Image Processing
  • Unix/Linux Command-Line Image Pipelines

More comparisons

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