ART and Sigmoid [solved]

I am just discovering the Sigmoid tone mapper function in Film Simulation in ART - and I am almost speechless at how fantastic this tool is.
If you switch on Sigmoid right at the beginning, there is no more clipping of the highlights, even if you then increase the brightness considerably in Tone Equalizer or with Exposure Compensation.
I have the impression that Sigmoid is a kind of guarantee that the lights will no longer break out.
In this example, I have also done some additional trickery: A mask in Color/Tone Correction on the painting so that it gets the necessary darkness again.
In this shot, the painter was almost in shadow and his painting was fully in the light, a difficult situation. I assumed that ART would help me - and the software does.
Of course, it’s also a matter of taste how much you want to compensate for the exposure contrast. I like it when the supporting leg remains very much in the dark, it makes the picture more mysterious.

I’m sharing the image with anyone interested in ART and the Sigmoid tool. I have to say: A very powerful tool for high lighting contrasts.

M1.dng (21.0 MB)
M1.dng.arp (60.1 KB)


I wouldn’t think to mask sigmoid …generally in DT I set middle grey and use it as a global tone mapper and just tweak contrast and skew…then use the tone eq and local contrast…

I would likely do some similar in ART I think…

Unless I misread @micha’s post, I don’t think they used a mask on Sigmoid. They turned Sigmoid on at the beginning of the edit, and then they used a mask with Color/Tone Correction.

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Todd, how would go about setting middle grey in ART?

I am much less familiar with ART in DT I rely on my eyes but more often now the exposure autopicker set to 50% on the whole image or a region of interest …In ART I would likely use my eyes or use the the heat map in the Tone Eq maybe as a guide… I might have a play and see… usually in ART I used DCP profiles and the tone curve in there rather than the automatch but now with sigmoid I guess there is another option…

Good point… you can use sigmoid from local or film sims and I guess I thought he was masking it but your right he may have just modified the brightness of the photo with a mask…

Sigmoid is so good! Would love to see it in Rawtherapee.

Did you want to add CC license to allow for some edits to be shared??

Yes, exactly like this: first switch on Sigmoid, then Ton Equalizer. But because the painting is so strongly illuminated by the spotlights in the exhibition, i.e. it is too brightly lit, I made a simple, rectangular mask and reduced the tonal values of the oil painting there with Color/Tone Correction.

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Moving the middle gray is incredibly easy with ART: Target gray point (brightness).
This tool really shifts the middle gray, i.e. the medium-light tonal values without affecting the lightest and darkest ones. A great tool!


You are welcome to download and edit the attached photo in this forum.
But I do not understand my contribution as a play_raw. My intention is not to see the most beautiful image developed, but to get to know the functions of ART better and better, especially Sigmoid.

It was probably confusing that I had also used a mask to darken the painting. It would have been clearer to just work with Sigmoid and Tone Equalizer.

I am particularly fascinated by the effect of Sigmoid, which prevents the lights from clipping.
And I would like to share my experience and joy with ART with you all.

And of course learn from you.

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I’m not too familiar with ART but I thought I would see how filmic behaves in ART as part of the processing… here is a quick swing at it from me… sounds like you are not intending a playraw so I will just add the arp file

M1.jpg.out.arp (18.1 KB)

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Your example is very interesting: even if you have balanced the contrast a little too much, I can see that the Tone Equalizer alone, with which you worked, immediately produces roughly the same quality as my Sigmoid.
Yes, in fact, Tone Equalizer is the better tool here.

But I don’t want to discourage you, @priort from uploading a dt version. Of course I also use darktable from time to time.

In short: I think I was a little too happy about the successes with Sigmoid. There are probably many better examples where this tool is superior to others.

I can see that the possibilities are endless (unfortunately this is also confusing).
This is my favorite: M1+Sigmoid+TE+Mask.dng.arp (11.9 KB)
The question that concerns me is:
When does Sigmoid make sense to use?

Log Tone Mapping also produces very good results:
M1+LTM.dng.arp (11.9 KB)

With respect to sigmoid its a very easy to use transform that fades nicely to white…generally preserves midtones … log tone mapping is doing the same sort of operation and as was explained a while back is a sort of modified filmic without the look curve… So I think it is just whatever tool gets you there… I think the initial version of yours highlights the art better for sure than what I ended up with. I don’t know what it is I just never like the vignette look even when it might make sense… so I guess I dialed that back and warmed it up a bit… of course having no idea what the lighting was actually like… :slight_smile:

Yes, not everyone likes the vignette effect. I like it because it leads the eye to the center. And since the room in this picture only consists of boring white walls, even more so.
As you say, I get there quickly with Simoid, but I still need to get to know the other tools much better. It is and remains exciting. Especially in exchange with you.

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I have for sure been helped so much on this forum from explanations, tips and resources shared by members… given the topic I won’t pollute it with a DT version… here is the xmp of what I hacked out in DT… I have taken to rendering them in relative and perceptual versions to see which I prefer… I use an icc from to do that as the DT icc has not table for that…
M1.dng.xmp (20.4 KB)

I didn’t use sigmoid in that edit I guess I should have … when I dont’ use it I use Filmic V5 or nothing but the tone eq…

It is there in Local Adjustments. The documentation is on RawPedia.

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Thanks for the dt version. Interesting how many different possibilities there are. Each one has something for itself. It only gets difficult when you have to choose one. That’s life.

Attention, important addition:
The nice thing about Sigmoid is that it has the brightest tones very well under control, alos prevents clipping - but only now I realize that the brightest tones are far darker than white!!! Most of the time the brightest areas are only just under 80%, which is far too little for a normal picture.

So you have to raise the brightest areas again. You can do this with Skew or with White point in the Sigmoid tool. But I still have to experiment before I can recommend anything.

I don’t really understand skew yet. With dt, the higher values should increase the contrast in the bright areas, with lower values in the shadows. I don’t yet know whether this is exactly the case with ART.

Just look in the sigmoid thread… I posted an example using the half sweep image and waveform display… You can easily visualize the curve and what it does as you move sliders. I’m on my phone but I’ll look it up later if you don’t see it