By the way, I asked Bing Chat about negative numbers in .cube files and here is the answer:
Yes, .cube LUT (Look-Up Table) files can indeed contain negative numbers. These negative values in the LUT file represent a decrease in the corresponding color value¹. For example, if a data row in the LUT file looks like this:
0.1201138 0.0000000 -0.0063639
And the original output color was:
vec3 = { 0.5, 0.5, 0.5 }
Then after applying the exact LUT data row on this output color, you should get:
outputColor = { 0.5 + 0.5 * 0.1201138, -> positive value thus positive color gain R
0.5 + 0.5 * 0.0000000, -> 0 thus neutral gain in G
0.5 + 0.5 * -0.0063639 -> negative value thus negative color gain in B }
This means that the red color component will increase, the green component will remain the same, and the blue component will decrease¹. However, it’s important to note that the interpretation of these values can depend on the specific software or shader you’re using to apply the LUT. It’s always a good idea to refer to the documentation of the specific software you’re using for precise information.
Source: Conversation with Bing, 14/12/2023
(1) What negative values in LUT mean and how to use them?. image processing - What negative values in LUT mean and how to use them? - Stack Overflow.
(2) 3d lut cube files fail to apply with error - cube lut lines number is … 3d lut cube files fail to apply with error - cube lut lines number is not correct · Issue #4420 · darktable-org/darktable · GitHub.
(3) HDK: Lookup Tables (LUTs) - SideFX. HDK: Lookup Tables (LUTs).
(4) Free LUTs Color Negative - free presets. Free Color Grading LUT "Color Negative" for Filmmakers & Photographers.