Working in 16-bit and 32-bit in Paint by Zaweba

Bit depth decides how many steps of tone each colour channel can hold, and it matters most when you push an image hard. In Paint by Zaweba you choose it when you create a document, because File > New has a bit depth setting, and you can change it later with Image > Mode, which switches between 8, 16 and 32 bits per channel in a single undo step.

An ordinary 8-bit image has 256 levels in each channel. That is plenty for a finished picture on a screen, but it runs thin when you stretch the tones. A strong curve, a heavy shadow lift or a long smooth gradient across a sky can break into visible bands, because there are simply not enough steps between one shade and the next. A 16-bit document has 65,536 levels per channel, so the same edit has far more room before anything shows.

When 16-bit is the right choice

Most people who edit photographs seriously work in 16-bit and only come down to 8-bit at the very end. It is the natural home for RAW files, which open as 16-bit documents through the RAW Developer, and for scans where you expect to make big corrections. It also suits illustration with soft airbrushed gradients, where banding would spoil a large area of flat colour.

The built-in filters run at 16-bit, so you lose nothing by staying there while you retouch, adjust and sharpen. The files are bigger and some operations take a little longer, but on a modern PC the difference is rarely something you notice while painting.

What 32-bit is for

A 32-bit document in Paint by Zaweba is linear light, and its values can go above 1. That means a highlight can be brighter than white, which is exactly what you need for high dynamic range work: editing renders from a 3D program, or keeping the detail inside a light source that an 8-bit file would clip to a flat patch. EXR and Radiance .hdr files open as 32-bit documents for this reason.

The trade is that not everything works there. Only 32 of the filters are offered at 32-bit, and some tools are greyed out while you are in that mode. A sensible habit is to do the tone work that needs the extra range in 32-bit, then switch the document to 16-bit with Image > Mode for the retouching and creative filters. Because the switch is one undo step, you can step back if you change your mind.

Exporting without banding

Most of the files you hand to other people are 8-bit: JPEG for photos, PNG for web graphics. When Paint by Zaweba exports a 16-bit or 32-bit document to an 8-bit format it dithers the result, scattering a fine pattern of noise across the conversion so smooth gradients stay smooth rather than stepping. You don't need to do anything to get this, and it is one of the main reasons to keep your working file at a higher depth and only drop down on export.

Keep the deep version as your master in the native .ptx format and export copies from it. If a client asks for a different crop or a brighter version later, you go back to the full data rather than editing an already compressed 8-bit file.

Habits that help

Decide the depth early when you know the job. A logo or a screenshot gains nothing from 16-bit, and a set of web buttons will be smaller and quicker in 8-bit. A landscape photo you plan to grade heavily, or a sky you want to recolour, deserves 16-bit from the start.

If a tool you want is greyed out, check the mode before anything else, because a 32-bit document is the usual reason. And if banding appears while you work, look at whether the document is still 8-bit: converting up will not invent lost detail, but it will stop further edits making the steps worse.

Deep colour is one of those settings that most people never think about until a sky goes stripy. Once you start working at 16-bit by default, that problem mostly disappears.