How can I stop clipped highlights turning blue/purple in RawTherapee?
Asked 10/22/2015
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2 answers
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When editing a Nikon D750 RAW in RawTherapee, very bright lighted areas that looked white in real life are rendering as blue/purple instead of white or near-white. The in-camera JPEG handles these highlights much better.
The affected pixels appear to have red and blue near saturation while green is much lower, so adjusting tint helps the highlights but damages the rest of the image. Is this caused by RAW color profiling or the way highly saturated highlights are mapped, and is there a way in RawTherapee to blend or tame these clipped colors so the highlights look more natural?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
1
The reason for them to look so terrible is aggressive profiling which needs to be done to bring the image data recorded by camera closer to the reality (the bad form of colour sensing to be specific), and it's imperfection is exceptionally obvious with saturated objects. This is very apparent in photos of recent Canon DSLRs because they tend to require strong profiling and will show up with any digital camera if light source is saturated enough. If it wasn't the case the light would look good as long as it is inside colour space of output file and inside colour space of output device.
Most output devices cannot reproduce the colour which is produced upon simple colour conversion and it needs additional manipulation to look fine.
Here are two verions from same file, one from Adobe Camera RAW and one from RawTherapee with custom weaker (less saturated) colour profile.
There is a way of making saturated bright sources look good - give tonal curve a wide shoulder and it will look natural. (your tonal curve will be different from the one displayed, experiment to find the one which you need)
You may also try different highlight reconstruction settings and also reduce saturation globally but the main way of improving saturated highlight is still tonal curve (or highlight compression which acts similarly).
Also, recent versions of RT sure have a profile for D750 and it is contained in camconst.json . You may either update RT or copy just one file from installation folder.
Originally by user49477. Source · Licensed CC BY-SA 4.0
user49477
10y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—this is usually a highlight/color-mapping issue, not necessarily a missing camera profile. With very saturated or clipped light sources, RAW conversion and profiling can push the recorded channels into unpleasant blue/purple colors, especially once the data is mapped into the output color space.
Based on the community answers, the practical RawTherapee fix is to use the tone curve option called Saturation & Value Blending. That helps blend extreme highlight colors toward a more natural result and is a common compromise for clipped colored lights.
Why it happens: camera sensors and profiling don’t record intense colored light perfectly, and strong profiling can make the problem more visible. The camera JPEG often applies extra highlight/color processing behind the scenes, so it can look better than the default RAW rendering.
So the best answer is: try Tone Curves → Saturation & Value Blending in RawTherapee to reduce the blue/purple cast in blown highlights.
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