PAM to EXR: conversion guide

What happens when you convert PAM to EXR?

Multiple source images

PAM 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.

An HDR container adds no captured range

EXR can hold HDR working or display values, but exporting an SDR image does not reconstruct clipped highlights or missing shadow detail. Numeric conversion, colour space and transfer function depend on the future engine. A wider container is not an automatic HDR enhancement.

Encoding mode

EXR supports lossy and lossless codecs. Choose one for the sample types and required precision; .exr alone does not guarantee exact channel preservation. EXR permits different encoding modes or container representations. Its format name alone does not promise lossless output, a quality setting or a size reduction. The future engine must choose a supported codec and sample representation; inspect the target’s compression notes below.

PAM

Source

PAM

Portable Arbitrary Map

Compression: UncompressedTransparency: YesMetadata: Header, Comments

Portable Arbitrary Map: simple uncompressed raster samples for image-processing pipelines.

Explore PAM format →

EXR

Target

EXR

OpenEXR

Compression: Lossy & losslessTransparency: YesMetadata: Typed header attributes, Chromaticities

HDR raster data for rendering and compositing, with named channels and lossless or lossy codecs.

Explore EXR format →

Is PAM → EXR right for you?

Good choice when

EXR fits your delivery use: Render passes & HDR compositing.
You can choose the source image or part needed for delivery.
You need an image in an HDR-capable working pipeline.
You need a transparency-capable destination and will check its supported variant.

Probably not when

You require a complete collection, page set or multipart round trip.
You expect new highlight or shadow detail from a container change.
You assume format-level alpha support guarantees matching transparent edges.
You need a guaranteed quality or file size before encoder settings exist.

PAM to EXR conversion details

Multiple source images: PAM 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.
An HDR container adds no captured range: EXR can hold HDR working or display values, but exporting an SDR image does not reconstruct clipped highlights or missing shadow detail. Numeric conversion, colour space and transfer function depend on the future engine. A wider container is not an automatic HDR enhancement.
Transparency representation: Both format profiles allow transparency, but this does not promise identical alpha representation. Source variants, target channel precision and alpha interpretation matter. The future encoder must explicitly carry or convert transparency; merely choosing EXR guarantees no alpha transfer.
Encoding mode: EXR supports lossy and lossless codecs. Choose one for the sample types and required precision; .exr alone does not guarantee exact channel preservation. EXR permits different encoding modes or container representations. Its format name alone does not promise lossless output, a quality setting or a size reduction. The future engine must choose a supported codec and sample representation; inspect the target’s compression notes below.
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: PAM: Uncompressed → EXR: Lossy & lossless PAM: 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. EXR: EXR supports lossy and lossless codecs. Choose one for the sample types and required precision; .exr alone does not guarantee exact channel preservation.
Transparency: PAM: Yes → EXR: Yes
Colour depth: PAM: maxval up to 65535 → EXR: HALF 16 / FLOAT 32 / UINT 32
HDR: EXR: Floating-point working values
Multiple images: EXR: Multipart
Dimensions: Pixel dimensions, page geometry, rendering resolution, resizing and orientation need explicit converter policies. The future engine has not defined them yet.
Metadata: PAM: Header, Comments → EXR: Typed header attributes, Chromaticities. Which fields are copied, rewritten or omitted will depend on the future engine; retention is not implemented yet.

Common questions

Will every source image be exported?

PAM 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.

Can EXR recover clipped highlights?

EXR can hold HDR working or display values, but exporting an SDR image does not reconstruct clipped highlights or missing shadow detail. Numeric conversion, colour space and transfer function depend on the future engine. A wider container is not an automatic HDR enhancement.

Which compression mode will EXR use?

EXR supports lossy and lossless codecs. Choose one for the sample types and required precision; .exr alone does not guarantee exact channel preservation. EXR permits different encoding modes or container representations. Its format name alone does not promise lossless output, a quality setting or a size reduction. The future engine must choose a supported codec and sample representation; inspect the target’s compression notes below.

Are bit depth and colour values guaranteed to match?

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.

Will metadata and colour profiles be retained?

PAM: Header, Comments → EXR: Typed header attributes, Chromaticities. Which fields are copied, rewritten or omitted will depend on the future engine; retention is not implemented yet.

Explore related PAM and EXR conversions.