How to use a .cube LUT file with Color Lookup?

Question

I have used "Image 2 LUT" to create a LUT for Unity from a certain movie. However, currently "Image 2 LUT" only outputs ".cube" files.

For HDRP, this is great, but for some reason, URP doesn't accept .cube file. URP expects specially laid out .png LUT file.

Is there any way to convert a .cube LUT file to a PNG that I can put into the slot of Color Lookup-> Lookup Texture with URP?

Unity expect this format:

The tutorial that Google finds and recommends is this.

However, I don't have Photoshop. Also, the tutorial deals with a square LUT that looks like this:

So even if I had Photoshop and I would follow the tutorial, I would still have a square LUT which is not laid out as Unity would expect it, so I did not use that tutorial.

How do I create a LUT png from a .cube file that I can use with URP?

Thank you.

Answer 1

Using GIMP, one can download and install this free add-on.

Restart GIMP.

Now import this neutral LUT in GIMP:

(Right click and select Save As)

Then select "Filter -> G'MIC-Qt".

Select "Colors-> Apply External CLUT".

Select your .cube file as "HaldCLUT Filename".

Click "Ok".

Make sure you don't apply the same filter twice by accident!!

Export the processed LUT png by choosing "File -> Export As..." Select ".png" and these settings:

In Unity, import the file and set the following settings: