Gradient Map and LUTs with Colour Lookup

Two adjustments in Paint by Zaweba change a picture's colours wholesale rather than nudging them. Gradient Map recolours a picture according to its brightness. Colour Lookup applies a LUT, a lookup table that maps every colour to a new one. Both are favourite tools for colour grading and stylised looks, and Paint by Zaweba can also turn your own grades into LUTs.

Gradient Map

Gradient Map takes the brightness of each pixel and replaces its colour with the colour at that point along a gradient. The left end of the gradient colours the shadows, the right end the highlights, and everything in between maps to the colours in the middle.

You choose the gradient in the gradient editor. A black to white gradient gives a straightforward black and white picture. A dark blue to cream gradient gives a cyanotype-like tone. A gradient with several colours makes a bold poster effect.

Reverse flips the gradient, so shadows take the light colours and highlights the dark ones. Dither adds a very fine noise to smooth the transitions and avoid visible bands.

Gradient Map is also useful at low opacity, or in a component blend mode, as a subtle grading tool. A warm to cool gradient at a low opacity can give a picture a filmic feel.

Colour Lookup

Colour Lookup loads LUTs in the .cube format (both 3D and 1D) and the .3dl format. LUTs are widely used in film and video for colour grading, so many photographers and video makers already have a collection.

Interpolation decides how colours that fall between the table's entries are worked out. Tetrahedral is the more accurate choice for most uses; trilinear is the classic method. If a LUT shows banding or odd transitions, try the other.

Six built-in looks come with the app. You can add your own by putting LUT files in the Presets luts folder. Any LUT dropped there is listed.

Exporting your own LUTs

File > Export > Colour Lookup Tables writes your visible adjustment layers out as a .cube or .3dl file. So you can build a grade in Paint by Zaweba with Curves, Hue/Saturation, Colour Balance and so on, then export it as a LUT and use it elsewhere, such as in a video editor, to get the same look on footage.

That's a powerful bridge. A photographer who also shoots video can match the two, and a look created on a still can be applied to many files in another program.

Working sensibly with LUTs

Treat LUTs as a starting point. Apply one, then lower its opacity or add adjustments after it to suit your picture.

Check exposure first. LUTs are designed for a certain range of tones, and a very dark or bright picture can give strange results.

When exporting a LUT, hide any adjustment layers you don't want included. Only visible ones are written. Masked adjustments can't be expressed as a LUT, since a LUT treats every pixel with the same colour the same way, so keep the grade global.

Banding, garish maps and other snags

Using Gradient Map at full strength with a garish gradient is the quick road to an unflattering picture. Try lower opacity.

Forgetting to dither on smooth skies can leave visible bands. Turn dither on.

And remember a LUT carries only colour mapping. Anything that depends on position, like a vignette or a blur, won't be in it.

Gradient Map and Colour Lookup bring film-style grading into Paint by Zaweba, and LUT export lets you take your looks anywhere.