Viewing HDR images with 32-bit preview in Paint by Zaweba

A 32-bit document holds more light than your monitor can show. Values above 1 are brighter than white, and a single image can contain a window blown far past white and a shadow corner almost at zero. To work on that, you need a way to look into different parts of the range. In Paint by Zaweba that is View > 32-bit Preview Options, which sets the exposure and gamma of the view live, without changing the pixels.

The last part is the key idea. The preview is a lens, not an edit. Turning the exposure down to see detail in a bright sky leaves the data exactly as it was.

Why HDR needs a preview control

A 32-bit document in Paint by Zaweba is linear light. That is how light behaves physically, which makes compositing and exposure maths behave properly, but it isn't how a monitor expects to receive an image. The view has to map that wide linear range onto the narrow range of the screen, and there is no single right mapping. Exposure slides the window up and down the range. Gamma shapes how midtones are distributed in what you see.

Without that control you would see either a blown-out picture or a murky one, and you would be tempted to fix it with real edits that change the data you wanted to keep.

Using exposure

Open an EXR or Radiance .hdr file, or switch a document to 32-bit with Image > Mode. Then open View > 32-bit Preview Options and move exposure while watching the canvas. Lower it to inspect the bright areas: a lamp, a sunlit wall, a specular highlight on metal. Raise it to check noise and detail down in the shadows.

This is particularly useful for retouching. If you are cloning out a reflection inside a bright window, drop the view exposure until the window has texture, do the work, then bring the view back. The repair will hold across the full range because you made it while seeing the detail.

Using gamma

Gamma changes the curve between dark and light in the view. A lower or higher setting can make it easier to judge midtones while you are matching a pasted element to a background, or checking that a gradient in a lighting pass is smooth. Treat it as a comfort setting for your eyes rather than a creative choice, because, like exposure, it doesn't affect the file.

Where it fits in a workflow

A typical HDR job in Paint by Zaweba goes like this. Open the 32-bit file. Use the preview to inspect the range and make the edits that need it. Then, when you want a picture for the web or for print, you make a real tone decision, either with adjustments or by switching the document to 16-bit, and the export is dithered down to 8-bit.

Remember that some tools are greyed out in 32-bit and only a subset of filters is offered there. Doing the range-dependent work first and dropping to 16-bit afterwards gives you the full toolset for finishing.

Things to watch for

It is easy to forget the preview is set and wonder why a picture looks dark or flat. If a 32-bit image looks wrong, check the preview options before reaching for an adjustment. Also, what you see with a high exposure isn't what an 8-bit export will look like; the export depends on the tone decisions you make in the document, not on the viewing lens.

Used that way, the 32-bit preview is simply a pair of hands on the dial. It lets you see everything in an HDR image while you edit, and leaves the data safe.