About PGM Files
PGM Grayscale Image
PGM (Portable Graymap) stores grayscale images in a simple ASCII or binary format.
Family
Raster & Vector Images
Extension
.pgm
MIME Type
image/x-portable-graymap
Can Use As
HOW PGM
CAME TO BE.
PGM — Portable GrayMap — is the grayscale sibling of PBM and PPM in Jef Poskanzer’s 1988 Netpbm toolkit. Where PBM stores 1-bit black-or-white pixels, PGM stores 8-bit (values 0-255) or 16-bit (0-65535) grayscale values. Like its sibling formats, PGM comes in ASCII (P2) and binary (P5) variants, and shares the same stupidly simple header: magic number, width, height, max value, then pixel data.
PGM has been the Unix grayscale intermediate format since shell pipelines needed one. OCR engines (Tesseract) preprocess scanned documents to PGM before recognition. Medical imaging pipelines convert DICOM images to PGM for ImageMagick processing. Machine-vision and photogrammetry tools exchange depth maps as 16-bit PGM. It’s a format that refuses to die because its simplicity is its best feature.
CURIOSITIES &
TRIVIA.
Tesseract OCR's preferred input format is PGM — every "scan to text" pipeline on Linux preprocesses through it.
Medical imaging workflows use 16-bit PGM to preserve the 12-bit output of X-ray and MRI scanners during intermediate processing.
A grayscale photo compresses 8× better as a 1-bit PBM if you dither it — but loses all tonal detail.
Machine-vision systems exchange depth maps as 16-bit PGM because the single-channel grayscale fits depth values naturally.
The P2 (ASCII) and P5 (binary) magic numbers are the only difference between two structurally identical file variants.
STRENGTHS &
LIMITATIONS.
Strengths
- Trivially simple to parse and generate.
- Ideal Unix pipeline intermediate for grayscale processing.
- Preserves 16-bit depth for scientific and medical data.
- Universal tooling (Netpbm, ImageMagick, Tesseract).
- ASCII variant is human-readable.
Limitations
- No compression — files balloon for large images.
- No metadata, no color profile.
- Grayscale only — drop to PBM for bitmap or up to PPM for color.
- Not a delivery format — strictly pipeline intermediate.
Typical Sizes & Weights
1920×1080 grayscale 8-bit (binary P5)
~2 MB
1920×1080 grayscale 16-bit
~4 MB
DICOM-equivalent medical slice
500 KB - 20 MB
Technical Specifications
- MIME type
- image/x-portable-graymap
- Extension
- .pgm
- Variants
- P2 (ASCII), P5 (binary)
- Bit depth
- 8-bit or 16-bit per pixel
- Creator
- Jef Poskanzer (1988), Netpbm toolkit
CONVERT FROM
PGM
Common Use Cases
Scientific imaging, machine vision
Related Formats
Popular comparisons
PGM vs JPG
Differences, file size, and when to choose each format.
PGM vs WEBP
Differences, file size, and when to choose each format.
PGM vs AVIF
Differences, file size, and when to choose each format.
PGM vs GIF
Differences, file size, and when to choose each format.
PGM vs BMP
Differences, file size, and when to choose each format.
PGM vs TIFF
Differences, file size, and when to choose each format.
Popular PGM conversions
The most-requested destinations when starting from PGM.
Frequently Asked Questions about PGM
Frequently Asked Questions
PGM (PGM Grayscale Image) is an image format used to store raster graphics — a two-dimensional grid of pixels describing a picture. It is part of the raster & vector images family and designed around a specific trade-off between file size, visual fidelity, and feature support (transparency, colour depth, compression type). Photographers, web designers, and content creators choose PGM when its particular strengths match the publishing target.
Most desktop photo viewers (Windows Photos, macOS Preview, GIMP, Photoshop, Affinity Photo) open PGM natively. On mobile, iOS Photos and Google Photos display PGM in the gallery when supported by the OS. If the format is rare or new, convert to JPG or PNG first — both are universally readable — using our PGM to JPG or PGM to PNG converter.
Upload the PGM to KaijuConverter and pick a target format (JPG, PNG, WebP, HEIC, TIFF, BMP, SVG, PDF). The conversion runs in the browser via ImageMagick and returns a download in seconds. No account or installation required; both input and output delete automatically within two hours.
It depends on the task. JPG is the smallest file size for photographs; PNG is lossless with transparency; PGM has its own niche that may favour colour depth, animation, or encoding efficiency over one or both of those. For the final web publish, test all three and measure file size plus visible quality on real content.