Chromatic adaptation OFX

[David Brown]

The CA plug-in seems like a very cool OFX that deserves to be explored. With a single slider move you can do a lot of heavy lifting on multiple variables based on a mathematical model of human vision. I understand that the "correct" use of the plug-in would be to transform an image so that it appears to be the same image (same colors) but under different lighting. For instance, I have  substituted the CA transform into Juan Malara's film emulation powergrade in place of two alternative nodes he provides to adjust white point. That seems like an intended kind of use.

As cool as that is, it seems like we might be able to do some interesting things that could not be dialed in manually.

Anyone using the CA plug-in for anything interesting or useful?

Thanks in advance.

[Zachary Medow]

Can this tool be used for the Judd offset? Or to convert from 709 primaries to p3?

[Marc Wielage]

We use the Chromatic Adaptation OFX plug-in to change baked-in 6500°K color temperatures on material that really should be 3200°. In Resolve 17, the Temperature & Tint controls in the Primary pallet were altered so they more or less reproduce what the Chromatic Adaption plug-in does.

You can also get some extreme looks with it, but you have to watch out for unexpected results and out-of-gamut issues.

[Anton Meleshkevich]

Chromatic adaptation plugin is a RGB gain multiply operation in linear gamma and in one of LMS color spaces you can choose from. This is the same tool as temp and tint in RAW, except for LMS, which is probably different and specific for particular sensor in RAW.

[Serhan Meewisse]

Does CA work similar to linear gain adjustments? 

Example operation:
Node 01 (CST from camera gamma to linear gamma)
Node 02 (Adjust white balance using gain wheel)
Node 03  (CST from linear to working gamma)

[Anton Meleshkevich]

20 minutes ago, Serhan Meewisse said:

Does CA work similar to linear gain adjustments? 

For gray scale only, so basically it's not identical, but very close. To be identical, after the linearization you also have to go from camera gamut to xyz, then to CAT02 using 3x3 matrix, then do gain (multiply) operation, then from CAT02 back to XYZ, then from XYZ back to camera gamut.

[Anton Meleshkevich]

On 4/6/2021 at 2:46 AM, Anton Meleshkevich said:

except for LMS, which is probably different and specific for particular sensor in RAW

Also, I was wrong here. Most likely (but not always I guess), white balance in RAW is the multiplication of the code values that come from sensor, hopefully before the debayering. So it's a gain operation in some linear color space, that has a native sensor gamut (which can be different between the actual units of the same camera model).

At least this is correct for Alexa V3. I mean, the part that WB is performed in camera vendor native gamut.

Edited October 31, 2023 by Anton Meleshkevich