How to apply a LUT to a photo
Paint by Zaweba applies .cube and .3dl LUTs through a Colour Lookup adjustment layer, and can export your own adjustments as a LUT for other apps.
Add a Colour Lookup adjustment layer and load the LUT into it. Paint by Zaweba reads .cube files, both 3D and 1D, and .3dl files, and applies them as an adjustment layer, so the photo itself is never changed. It can also go the other way: File > Export > Colour Lookup Tables writes your own visible adjustment layers out as a .cube or .3dl LUT.
A LUT, or lookup table, is a recipe that maps every input colour to an output colour. Video editors use them for colour grading, and photographers use them to give a set of pictures one consistent look, or to match stills to footage graded with the same LUT.
What you need
The LUT file and Paint by Zaweba on Windows. LUTs come from camera makers, video tools, colourists and your own grading. The program is free and offline, so there's nothing to sign into.
Step by step
Open the photo. Add a Colour Lookup adjustment layer from Layer > New Adjustment Layer or the Adjustments panel. In the Properties panel, load your .cube or .3dl file. The look appears at once.
Because it's an adjustment layer, you can lower its opacity to soften the effect, which is often needed since many LUTs are strong. You can also mask it to keep the effect off skin or a product whose colour must stay true, and switch its blend mode to Luminosity or Colour to apply only the brightness or only the colour part of the grade.
Keeping your LUTs handy
Six looks are built in. If you have a collection of your own, drop the LUT files into the luts folder in Paint's Presets, and every one is listed in the Colour Lookup layer, ready to choose without hunting through folders.
Colour Lookup offers tetrahedral or trilinear interpolation. Both work out colours that fall between the table's points. Tetrahedral is generally the more accurate of the two and the safer choice for smooth gradients.
Making your own LUT
Grade a photo with adjustment layers: curves, hue and saturation, selective colour, a channel mixer, whatever gives the look you want. Make sure only the adjustments you want in the LUT are visible. Then choose File > Export > Colour Lookup Tables and save as .cube or .3dl.
That file now carries your look. Load it in a video editor to match footage to stills, share it with someone working in another program, or use it back in Paint on a different photo.
Only colour adjustments translate into a LUT. Anything that depends on position or neighbouring pixels, such as a vignette, a blur, a mask or sharpening, can't be stored in one.
Getting a good result
LUTs expect a certain starting point. A LUT made for flat log footage will look wildly over the top on an ordinary JPEG. If the result is far too strong or oddly coloured, the LUT was probably made for a different kind of input. Turn down the opacity or choose a LUT made for normal photos.
Correct exposure and white balance first, with adjustment layers below the Colour Lookup. A LUT applies the same mapping everywhere, so it can't fix a photo that started out too dark or too blue.
Related tools
Gradient Map, in the same family of adjustments, recolours a picture by brightness using a gradient, with reverse and dither options. It's a simpler way to make duotone and split tone looks. Quick Looks offers one-click looks for when a LUT is more than you need. For matching a look across stills and video, though, a LUT in Paint by Zaweba is the most portable answer.
