New Sigmoid Scene to Display mapping

[nosle]

@qmpel

If you have a photo with high dynamic range, it is more fiddly, to get a pleasant curve - but I still wouldn’t call it a lot more work.

Sorry I assumed high DR images or plenty exposure pushing because with low DR the tone mapping should basically be a no op with any visible difference coming from the tone curve part of sigmoid/filmic so basically just a base curve?

[priort (Todd Prior)]

No I just set the background to as close to black as I can and set the channel colors to be brighter…this you can do with css… the alpha to brighten the whole thing has to be changed and then compiled… you can find the lines that control the various things related to the histogram in darktable.css

[age]

Hi!
I just want to share some observations, I think it would be a good idea restoring the luminance after the rgb tonemapping.

The issue is that rgb per channel tonemapping becomes a little destructive when the saturation increase.

An example:

This is an image tonemapped with rgb tonemmaping

If we desaturate the already tonemapped image we obtain this

If we desaturate the original hdr image and we do the tonemapping after, we could get a more detailed image

Now the idea is to remove the luminance from the rgb tonemapped image and add the luminance tonemapped image

(Note that this particular image has issues with out of gamut colors)

A simple way in pseudo code to obtain this without actually decomposing the image is :

i=Original_image

Lum= get luminance from i
tm_lum=tonemapping lum

tm=tonemapping i (with or without hue preservation)
Lum2= get luminance from tm

tm_luminance_restored=tm/lum2*tm_lum

[jandren (Jakob Andrén)]

Interesting idea, some questions.

Has anyone else done this that you can link to?

Is the bottom image processed exactly as described?

What to do with colors that get pushed out of display gamut?
We will have the same problem as rgb ratio with no gamut mapping even though there will be a desaturation of bright pixels. Have a feeling that f ex skies will look desaturated even after this operation.

[age]

@jandren

Has anyone else done this that you can link to?

I don’t think

@jandren

Is the bottom image processed exactly as described?

Yep

@jandren

What to do with colors that get pushed out of display gamut?

Good question, ideally I think that extreme saturation should be fixed before tonemapping with something like a proper dual illuminant profile

[ggbutcher (Glenn Butcher)]

@jandren

What to do with colors that get pushed out of display gamut?

Let the display transform deal with them.

[age]

@age

A simple way in pseudo code to obtain this without actually decomposing the image is :

After more testing with very OOG flowers this could produce little color banding artifacts, I see this problem only with flowers photography.
Using CIE lab or the simple ycbcr color spaces solves the problem.