Lookup Table Generator

Create Lookup Tables (LUTs) from images.

I wrote this script so that I could take Adobe LightRoom settings, convert them into lookup tables, and use them to color grade videos. It should work for other things as well though.

The basic idea is that you can feed this program the path to your image file containing your color settings and it will generate a Lookup Table and store it in a new .cube file in the current directory.

For example, if your file's name is hald.jpg, then this script will create a new LUT titled hald.cube

Example

require './lut_generator'

LUTGenerator.create_lut('path/to/your/image')

How it works

Before generating a Lookup Table, you'll need to create a HALD image that you can use to apply your color settings to. You can use the method in this class if you'd like:

  LUTGenerator.create_hald

This method is just a thin wrapper around an ImageMagick command to create a new hald file:

convert hald:8 hald.jpg

This will create a 512x512 jpg. You can adjust this as well. For example, this will create a 125x125 png:

  LUTGenerator.create_hald(5, 'png')

Once you have a hald image, you can add it into Adobe LightRoom, apply your color settings onto it, and export the image with the effects. This is the file you'll run through LUTGenerator#create_lut to create your LUT.

At this point, all you should need to do is trigger the call method, passing in the path to your image file:

  LUTGenerator.create_lut('path/to/your/image')

Check in the current directory after running this and you should now have a new LUT file with a .cube extension. You can now take this file and use it to color your images and videos.

Use it with FFmpeg

Here is an example of how you can use your new lut file to color a video using FFmpeg:

ffmpeg -i input.mp4 -vf lut3d=file=path/to/your/lut.cube output.mp4

Dependencies

This code is dependent on ImageMagick and the ruby gem RMagick.

Install ImageMagick:

brew install imagemagick

Install RMagick:

gem install rmagick

Notes & Sources

I spent a good bit of time trying to figure out if/how I could write my own image-to-lut converter in ruby. Here are some of the documents, projects and tools that ultimately helped me to fill in the missing peices:

• Cube LUT Specification (Adobe)
• LUT Convert by Mike Boer (Python)
• ImageMagick
• RMagick