lut_maker is a Python CLI tool for generating 3D RGB color look-up tables (LUTs). Such a table can capture the 'look' of anything that alters color, such as a set of Photoshop adjustments, or a particular analog film. The LUT can then be used as a 'filter' in tools such as Adobe Photoshop, Adobe Premiere, or OpenGL. Think of it like an Instagram filter.

This tool is currently crazy alpha, and is missing a lot of the fancy stuff needed in a pro workflow.

Python >3.4 only at the moment.

Install the CLI tool from PyPi:

pip install lut-maker

Navigate to the directory where you want the measurement assets to be created, and then issue the lut_maker new command (the defaults are sensible).

mkdir my-lut
cd my-lut
lut_maker new

Modify the resulting lut_measurement_0.png file to change the colors. Just keep in mind to only make adjustments that are applied to every pixel equally, such as curves, levels, saturation, contrast, brightness. Position-dependent effects such as blurs, clarity, 'local contrast' etc. are not valid.

In this example, I'll expose lut_measurement_0.png onto polaroid film and then scan, align, and save it back into the same file.

When you are happy with your color modifications, in the same directory run:

lut_maker compute

That's it! The newly created lut.* files are ready for use. A few guides:

• How Do I Apply 3D LUTs in Adobe Photoshop?
• Using Lookup Tables to Accelerate Color Transformations (GPU)

Here is a LUT based on Impossible Project Color polaroid film, applied to an image in Photoshop:

The generation step generates a uniform 3D lattice filling the entire linear 8bpc RGB space. In many cases it is impractical to sample/transport/store every location (256^3 = 16777216 samples). A common standard is to sample only 17 locations along each color axis, and then later interpolate between them. You should only need to use more than the default 17 if the modifications you make are extreme or discontinuous.

Using the default settings will generate 3 files:

• lut_alignment_guide.png - transparent overlay that shows the sampling locations, to help you align an analog photo/scan
• lut_measurement_0.png - the palette image to be modified
• lut_metadata.json - metadata about the LUT, used by later steps

The defaults are sensible for most cases, but the lut_maker new command has the following options:

--name TEXT           Name of LUT to generate
--lut-size INTEGER    Size of each dimension in 3D LUT
--image-size INTEGER  Width & height of square output image in pixels
--stack INTEGER       Number of unique measurement palettes to output
--data-dir TEXT       Location for LUT files

If you will be modifying the measurement assets using an analog technique, it will probably susceptible to imperfections from dust, vignetting, chromatic abberrations scratches etc. To help combat these, increase the --stack setting from the default of 1. This will output multiple measurement images, each with the positions of the colors randomized. During the compute phase, it will average the results from each image together to create the final LUT.