rework color LUT explanation

[ScanMountGoat]

Rather than focus on the technical aspects, it will be easier to describe LUTs as a gradient map. The advantage of a LUT over a gradient map is that the RGB channels can be controlled individually. This can be demonstrated by applying a gradient map adjustment layer to a LUT and associated stage and then showing the additional control not possible with a gradient map.

[ScanMountGoat]

The color grading LUTs can use their own dedicated page with a summary, intuitive explanation with gradient maps, and then the full technical details.

[ScanMountGoat]

There are two ways to think of the LUT transformation. It may be helpful to give images for both. Both examples start with an identity LUT (each input maps to itself). Applying a simple transformation such as decreasing saturation or a sepia tone will demonstrate the differences clearly.

1. The XYZ positions remain the same but the colors change
2. The XYZ positions and the colors change