HaldCLUT vs. Color Toning -- Colors not identical

Hi,

I didn’t like the colors produced by either “Camera Standard” or custom profile “Adobe Standard” for my Panasonic LX100 so I did some tweaking using the Color Toning / Color correction regions tool.

In order to free up the Color Toning tool for other purposes, I created a HaldCLUT image in RT, following the instructions in Rawpedia. However, when applying this HaldCLUT image to a picture using the Film Simulation tool, the resulting colors are not identical to the ones I have when using the Color Toning tool directly. Differences tend to get more pronounced as I apply other corrections, e.g. Exposure Compensation or White Balance, sometimes even resulting in pronounced color shifts.

Is there a reason for this? If so, is there a way to avoid this? Or am I doing something wrong?

Regards,
Bezier

Can’t help you with your problem (although at a wild guess, it might be something to do with the fact that film simulation and colour toning appear at different places in the pipeline, so are influenced differently by the other settings that you have).

I also have the Panasonic lx 100 so I was curious what changes you decided to apply.

I tend to use ART or darktable but both can use HALDCLUTS

Did you use masks in your color correction? I suspect this might be problematic.

I know nothing about RT, but I suppose the Color Toning tool uses formulae to calculate the transformation. A Hald CLUT is a lookup-table with a finite number of samples, and interpolation when the colour to be transformed isn’t one of those samples.

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Yes, I did. From my understanding of how HaldCLUT works, I would assume that the masks “find” the right colors in the Identity.tif, and transformations are done correctly.
But then, I don’t know more about this than what I read in Rawpedia.

Color perception is highly individual, so what works for me doesn’t necessarily work for you.
The following is based on the use of “Adobe Standard” profile.

  • A general slight shift of the entire image from green to blue.
  • A shift of blue tones in the direction of purple, together with a de-saturation.
  • A substantial de-saturation of purple-ish tones.
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I mentioned above why Hald cluts will generally give different results to formulae. There is another possible issue.

The thread HaldCLUT link is not working - #5 by Mira_Studio has a large zip of Hald cluts. These have 8 bits/channel/pixel. So precision has been lost, due to rounding to 8 bits. However good the interpolation is, we can’t get that precision back.

8 bits is okay for a final output. We won’t notice that loss of precision. But if we are further processing the result, the loss can cause problems. The heavier the processing, the greater the problems. This may explain:

Differences tend to get more pronounced as I apply other corrections, …

I doubt that it is related to the 8bit precision – the differences are way to big for that.

I found that I get better results when I set Mask Blur in the Color correction regions to the leftmost value of -10. I thought that 0 already meant “no blur”, but apparently this is not the case.

Still, the result is far from identical. With manual tweaking of the Color correction regions I managed to get an acceptable (though still not nearly identical) result with which, I think, I can live for the time being.

Nonetheless, it would be interesting to know what really is the reason for the very obvious differences. Is it just the way it is, or am I doing something wrong?