Hello (Excuse my bad english).
I continued the harmonization between “LA cam16” and “Abstract profile”.
After making it possible for illuminants and primaries to have an identical selection, I added to “Abstract profile - Color Tab”, 2 components present in “LA cam16”:
- “Midtones”: adds midtone control to the TRC - Tone Response Curve;
- “Smooth highlights”: gives you the option of lowering (softening) highlights. Note that this has nothing to do with the Exposure Tab - Highlight reconstruction (Inpaint Opposed, Color Propagation, etc.), which attempts to “reconstruct” colors that have disappeared on the sensor. The idea here is to lower highlights when they are high, to make the image more legible.
The (overall) differences between “LA cam16” and “Abstract Profiles”:
- very little in terms of algorithms: the “Source data adjustments (Local tab)” and “Abstract profiles (Color Tab)” modules are very similar.
- their position in the pipeline is different:
** LA cam16" is almost at the beginning of the process, just behind “White balance”.
** Abstract profile" is at the end of the process, just before “Color Appearance & Lighting”.
- their integration with Ciecam is different:
** integrated into the same tool for “LA Cam16” with simpler tools in Ciecam.
** separated between “Abstract profile” and “Ciecam”, with Ciecam’s many (too many) possibilities.
- but what they have in common is that the starting point is after the White-balance (I recommend in most cases “Temperature correlation”).
There’s nothing to stop you using both … 
“La Cam 16” and “Abstract profile + Ciecam”: an alternative to other tools such as “Log encoding” or similar, “Sigmoid”, etc. :
Why do I say this?
- It is necessary both to be able to “reduce” the apparent DR (dynamic range), and to maintain a colorimetry that is not too degraded.
- In many writings, it is said that a linear approach should be favored as much as possible:
** Logarithmic coding (unless mathematics has evolved?) or Sigmoid (which uses exponentials) are anything but linear transformations. I’m not saying they don’t work (you’ll find both in “LA Cam16”), but they do induce transformations in contrast and colorimetry.
** The TRC (Tone Response Curve), one of the 3 parts of the most common ICC profiles, contains a linear part (slope) and a parabolic part (gamma). The linear part brightens shadows, while the parabolic part simulates human vision. Almost all ICC profiles come with the 2 usual TRCs, sRGB (slope= 12.93 gamma=2.4) and BT709 (slope=4.5 gamma=2.22). Try it and you’ll see the difference.
** I’ve modified this TRC to make it suitable for processing images with (fairly) high dynamic range, especially those with blocked shadows. “Slope” can reach very high values (300 or more) and “gamma” high values (15 …). This enables absolutely linear retouching of shadows, and progressive retouching of highlights. This does not mean that the noise will not rise, or any other malfunction.
** As nothing is perfect, I added 2 components: a) one to act on the midtones; b) one to soften the highlights.
** Of course, this approach is not without its difficulties. Images with (very) high dynamic range (DR > 13) or highly differentiated luminances can be poorly processed (as can Log or Sigmoid coding). Nevertheless, this TRC combined with Ciecam is capable of rendering DRs in excess of 20 Ev.
** The possibility of using Ciecam, which simulates (at best) human vision at the phisiological level, is a more than interesting option.
** But getting down to basics with 4 simple settings solves most of the problems of difficult images.
What is Abstract Profile?
When I initiated this module, in late 2020, early 2021, there was a lot of criticism (to put it mildly). I was asked or told: 1) to withdraw this module (isolated request); 2) what’s this bullshit; 3) and so on.
The basic idea is to apply a virtual ICC profile to the data inside the pipeline. You know the input profiles (Input - ICC or DCP) to calibrate the camera. You know the output profiles for driving screens/printers. “Abstract profile” is a virtual profile that applies to data and modifies neither the “Working profile” nor the output profiles.
It is made up of 3 components:
- the TRC, which takes into account human vision for luminance restitution.
- the illuminant (D50, Tungsten, etc.) to take account of shooting conditions (sun, shade, etc.)
- primaries (AdobeRGB, sRGB, Prophoto, Rec2020, JDCmax, etc.) to select the range of colors taken into account (gamut).
An article on this subject:
https://www.johnpaulcaponigro.com/blog/17781/using-color-management-color-adjustment-synthetic-profiles/
You can act on these 3 components.
In the basic version, you have access only to the luminance components: “gamma”, “slope”, then “midtones” and “smooth highlights”.
You can act on the primaries. The difference with other approaches is that, here, you can modify them directly, modifying saturation (distance between the white point and one of the 3 vertices of the CIExy diagram) or hue by moving one of the vertices perpendicularly (or not) to the saturation vertex. The primaries (unless I’m mistaken) are the standardized ones shown on the CIExy diagram.
I’m not going to repeat the presentation of this concept and the tools described in Rawpedia - even if, obviously, the latest modifications are incomplete, and tutorials are pending.
https://rawpedia.rawtherapee.com/Color_Management#Abstract_Profiles
Yes, but Ciecam is what, and it’s complex.
I’m referencing an answer I gave in “Is Rawtherapee complex?”
https://discuss.pixls.us/t/is-rawtherapee-complex/42183/39
Try LAcam16 and/or Abstract Profile (with or without Ciecam) and you’ll see.
Executables :
https://github.com/Beep6581/RawTherapee/releases/tag/pre-dev-github-actions
This PR is quite voluminous in terms of modifications, but I don’t see any other way of doing it. Cutting it into several pieces wouldn’t make sense. Of course, it will complicate the review (@Lawrence37 , …)
Jacques
