HEIC to PGM: conversion guide

What happens when you convert HEIC to PGM?

Is HEIC → PGM right for you?

HEIC to PGM conversion details

Multiple source images

HEIC can contain multiple image representations with different roles. These are not automatically a timed animation. Selecting an image, preserving a collection or creating several outputs needs explicit engine support; neither a first-image choice nor an all-images export is implemented.

Animation becomes a still

An animated HEIC has a timed sequence; PGM is a still-image destination in this workflow. A still export loses motion and timing. Frame choice, blending and disposal must be defined by the future engine; a first-frame export is not promised.

Grayscale output

PGM stores one grayscale sample per pixel, with no colour channels or alpha. Colour input becomes gray; brightness depends on the colour transform and transfer-function handling chosen by the future engine. Higher maxval can retain more gray levels, but does not retain chromatic information.

HDR to SDR

If HDR source content is exported through an SDR representation, it needs a display rendering. Values outside the output range require tone mapping, scaling or clipping; brightness relationships can change. Tone mapping, exposure and colour handling depend on the future engine. Renaming or lossless compression cannot preserve out-of-range values.

Opaque output

If HEIC contains transparency, PGM cannot retain it as transparent output areas. Those pixels need compositing against an opaque background. Matte colour, alpha interpretation and edge treatment are future engine decisions; no background colour is selected yet.

Lossless sample storage

Netpbm stores these samples without compression. Reducing colour, thresholding or changing maxval can still lose information before storage; text and binary representations change the layout, not its image meaning. PGM can store its supported image samples without lossy compression. This applies after rendering and sample conversion: it does not guarantee preservation of source precision, colour space or document structure, and cannot undo earlier losses.

Sample precision & colour

Source and target sample models can differ in precision, channel layout, colour space and transfer function. Lossless compression only preserves the samples actually encoded; a precision reduction or colour conversion can already change them. The future engine defines numeric mapping, orientation and colour conversion; canonical depth facts are listed below where available.

Metadata & colour

Format support does not guarantee that an export preserves metadata or colour profiles. Retention and colour handling depend on the future converter; its engine is not implemented yet.

Compression

HEIC: Lossy & lossless → PGM: Uncompressed HEIC: HEIC commonly uses lossy HEVC; HEVC also has lossless coding tools. Actual quality, bit depth and chroma depend on the encoded profile and settings, not on the .heic extension. PGM: Netpbm stores these samples without compression. Reducing colour, thresholding or changing maxval can still lose information before storage; text and binary representations change the layout, not its image meaning.

Transparency

HEIC: Yes → PGM: No

Animation

HEIC: Yes → PGM: No

Colour depth

HEIC: Codec/profile dependent → PGM: maxval up to 65535

HDR

HEIC: Codec/profile dependent

Multiple images

HEIC: Collections & sequences

Dimensions

Pixel dimensions, page geometry, rendering resolution, resizing and orientation need explicit converter policies. The future engine has not defined them yet.

Metadata

HEIC: Exif, XMP, ICC, NCLX → PGM: Header, Comments. Which fields are copied, rewritten or omitted will depend on the future engine; retention is not implemented yet.

Common questions