À propos des fichiers PGM

PGM (PGM Grayscale Image · Format d'image)

Lancement 1988 Par Jef Poskanzer

PGM Grayscale Image (.pgm) est un format de fichier pris en charge par KaijuConverter pour l’archivage, l’échange professionnel et la conversion multiplateforme.

Famille

Raster & Vector Images

Extension

.pgm

Type MIME

image/x-portable-graymap

Utilisable comme

Entrée Sortie

L'histoire

COMMENT PGM
A VU LE JOUR.

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.

CURIOSITÉS ET
ANECDOTES.

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.

POINTS FORTS ET
LIMITES.

Points forts

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.

Limites

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.

Tailles et poids typiques

1920×1080 grayscale 8-bit (binary P5)

~2 MB

1920×1080 grayscale 16-bit

~4 MB

DICOM-equivalent medical slice

500 KB - 20 MB

Spécifications techniques

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

CONVERTIR DEPUIS
PGM

pgm jpg pgm png pgm webp pgm avif pgm gif pgm bmp pgm tiff pgm ico pgm pdf

Cas d'usage courants

Scientific imaging, machine vision