Opening EXR, HDR, RAW and FITS files in Paint by Zaweba

Files with a lot of data deserve a document that can hold it. Paint by Zaweba opens several specialist formats straight into the right kind of document, so nothing is squeezed down to 8-bit on the way in. EXR and Radiance .hdr files open as 32-bit documents, RAW files open as 16-bit documents through the RAW Developer, and FITS astronomy files open as 16-bit.

Each of these formats comes from a different world, and it is worth knowing why each one lands where it does.

EXR and Radiance HDR

OpenEXR is the standard image format of visual effects and 3D rendering. It stores high dynamic range values, so a rendered lamp can be many times brighter than white and still hold its detail. Radiance .hdr is an older HDR format often used for environment maps and panoramas used to light 3D scenes.

Both open in Paint by Zaweba as 32-bit linear light documents, so the extra range survives. Multi-part EXR files, the kind a renderer writes with separate passes such as diffuse, reflections or shadows, open as layers. That makes it straightforward to rebalance a render: you can stack the parts, change a blend mode or opacity, mask one pass, and see the effect at once rather than rendering again.

When you look at these documents, use View > 32-bit Preview Options to set the exposure of the view without altering the data, and remember that some tools are greyed out at 32-bit.

RAW camera files

A RAW file is the sensor's data before the camera has made decisions about white balance, contrast and sharpening. Paint by Zaweba sends RAW files through its RAW Developer, where you make those decisions yourself, and they arrive as 16-bit documents. With 65,536 levels per channel you have room to lift shadows and recover highlights without the banding an 8-bit file would show.

A good order of work is to get exposure and white balance right in the developer, then do local retouching and creative edits in the main editor with layers, masks and adjustment layers. Keep the result as a .ptx master and export copies.

FITS for astronomy

FITS is the format observatories and astronomy cameras use. Amateur astrophotographers meet it whenever they shoot deep sky objects with a dedicated camera. These files often look almost black at first because the interesting signal sits in a narrow band at the bottom of the range. Opening them at 16-bit gives you the depth to stretch that faint signal up with curves and levels and bring out a nebula or a galaxy without breaking the background into steps.

Choosing what to do next

Once a file is open, the document behaves like any other in Paint by Zaweba. You can add adjustment layers, paint, mask and retouch. The difference is the headroom. A 32-bit document is the place for tone decisions that need the whole range; a 16-bit document is the comfortable home for most retouching, since the built-in filters run there.

If you need the full toolset, it is usually best to make the range-critical decisions in 32-bit, then switch to 16-bit with Image > Mode, which is a single undo step.

Pitfalls with high range files

Exporting straight from an HDR document to JPEG without deciding how the tones should look is a common one. The export will be dithered to 8-bit, but the brightness mapping is still your call, so make it on purpose with adjustments first.

Another is flattening a multi-part EXR too early. Keep the passes as layers until the balance is right, because that flexibility is the reason the format was used in the first place.

All of this happens offline, on your own PC, with no account and no upload, which suits studios with confidential renders as much as hobbyists with a night sky.