Port JzCzhz from RawTherapee

[Former user]

RawTherapee currently has a branch with JzCzhz CAM for local adjustments and a PR is already open. Would be nice if ART also had it

https://github.com/Beep6581/RawTherapee/tree/lagamciemask2

https://github.com/Beep6581/RawTherapee/pull/6377

[agriggio]

Hi,

I tried using Jzazbz instead of Lab in the past, but I didn’t see much benefit to be honest, at least for SDR output. As far as I know, the advantage of Jzazbz should be much clearer for HDR output, but I have no way of testing that, so I don’t really know… on the negative side, converting to/from Jzazbz is quite expensive computationally, at least if done naively.

So, overall: I’m not really convinced of the benefits, but I would be happy to be proven wrong. I need to see some examples though

[Former user]

I think it would be great if ART and other RAW converters had HDR support in the future, and Jzazbz could be a step towards that goal.

While computationally expensive, it will be used only by those people who know what it does and how much processing time it takes. Personally, it runs on my PC just fine, and there are people with much more powerful setups than mine.

What about examples, try it with a low light high dynamic range photo. The difference might seem subtle, but it makes processing much easier, at least for me

[agriggio]

Hi,

as I wrote above, the only chance of this to happen is if somebody makes a convincing case for it. Which means that someone needs to:

1. show examples of why it is a good idea – saying “just try this or that” is not an example, because I have already tried and I am not convinced yet.
2. make a concrete proposal of where Jzazbz could be used and how. E.g. is this supposed to be a new tool, or is the idea that Jzazbz will be used where Lab is used now? And so on… again, “see rawtherapee” is not a proposal. If I wanted the RT way, I would simply use RT…

Sorry if I sound harsh, I don’t mean to. I just want to make my point of view clear…

Best

[Former user]

Sorry, I should have been more clear. I originally wanted Jzazbz to be a local adjustments module for chromatic adaptation, but if you can use it in other places like in Darktable that could also be great. I am unable to provide a screenshot right now but with this photo https://discuss.pixls.us/t/sodium-vapour-lamp/26925 (edit: and this one https://discuss.pixls.us/t/fight-with-artificial-lights/26906) just turning on Color appearance - Scope 100 - Jz Cz Hz in RT compiled from that branch brightens up the picture quite noticably and desaturates the colors. The end result should be close to how it looked in real life I think. If one's goal is to show the scene as is or close to that, that tool could be very useful in such cases.

And speaking of HDR, should I open a separate issue for that as a future goal? Mpv just recently added HDR passthrough to display and it already works at least on Windows

[agriggio]

I have just added a new “Perceptual” mode to the “color/tone correction” tool, which uses Jzazbz to apply color corrections (hue shift, color wheel and input/output saturation)

[Former user]

Thank you, compiled and it works great, I would even say it is a good alternative to Log Tone Mapping. Could you please add automatic CAM mode where it sets the sliders based on scene conditions?

[agriggio]

Hi,

sorry but what you ask doesn’t belong to the color/tone correction module. In fact, I have no plans to include that in ART, sorry. (I just don’t know enough about CAM to be confident including a tool based on it)

[Former user]

Ok, no problem, thank you for including at least color correction based on it. Closing this issue