What should be blend mode for Tone curve when using Parametric option

I want the Tone curve to affect only fore ground but not sky. So I created a mask using “Parametric” option. But I do not know what blend mode to choose. Please help me in that.

Pic shows yellow on sky. I will invert the mask so that foreground gets selected. But I do not know what should be the blending mode.


Blend mode is usually left on normal. If you can elaborate more on what you would like to do, we could show you some example workflows.

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Maybe this will drop a hint to some of the Youtubers to make a video on the blend modes. Your plan on selecting the sky , then inverting the mask is certainly a good approach. A little playing with the feathering and blur sliders will help to fine tune it. If your plan is to brighten the fore ground, you could switch to “screen” or “addition” without even touching the curve, to do this. On the other hand , if you wanted it darkened, you could use “multiply” or “subtract” to do that, also without changing the curve. Adjusting the curve and the opacity slider will get you towards something realistic looking, maybe. There’s plenty more modes that i completely don’t understand so I won’t even try to go there. I’m really not the teaching type. Hope this helps.

Here is the original image. I just want to brighten the foreground without blowing the sky. So i thought of selecting sky, then invert and then apply Tonal correction. I am using this image to learn how apply the technique that I just described. If this technique works, then I will apply this technique to other images also. If you can think of other techniques, please let me know. Note: I do not know how to apply drawn mask. I am comfortable with Parametric masks.


Thanks Stephen.

I used “screen” or “addition”, and it took me close to what I wanted. But it modified both foreground & background(sky) even though I had eliminated sky from equation by using mask. I would like to know why mask does not seem to take effect in case of Tonal correction. It works as expected in case of Noise_reduction & High pass filter.

Just click on the ‚+‘Icon right of the slider to invert the selected range

I’m not sure if this is allowed but I guess we’ll see. I took your jpg and did a tone curve adjustment on it using addition blend mode. Notice that to invert the mask I had to go below the parametric mask sliders and change it to “exclusive and inverted.” You should submit this for Play Raw and others here which are way better than me will work some of their magic.

aba5c92b3c55c4a1d23c4148130c7c70454219e4.jpeg.xmp (1.9 KB)

You can just ask the YouTubers for tutorials, @TheStoryOfRico, @s7habo, @Bruce_Williams, anyone want to make a video on blend modes? :slight_smile:

Also blend modes are more or less the same across image editing applications, so there are videos for other, more proprietary apps that are applicable to gimp/darktable/etc

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Great suggestion. It’s in my planning but I haven’t gotten to it yet since it’ll take me some time to produce. The most easy way to demonstrate it is in GIMP with black and white layers. All those options are basically divided in menus like saturation, contrast etc.

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For your desired results, there are a couple of possible alternative approaches, including but not necessarily limited to:

  1. the in-development tone equalizer module followed by a local contrast enhancement (note that this is not yet merged to DT master branch)
  2. Under the assumption you’re starting from a RAW, export multiple images at varying exposure shifts (+0, +1, +2, +3EV perhaps, or +0,+2,+4) and then feed those images to enfuse
  3. @Edgardo_Hoszowski has been continuing the work I started on fixing the exposure fusion function in basecurve by splitting it into a separate module with some serious code cleanups. This is another thing that isn’t yet merged to darktable’s git master

I would not recommend the current exposure fusion function in basecurve… It rarely provides desirable results for a variety of reasons. If you want to use a released version of DT, item 2 is your best bet.

I BELIEVE, but I’m not sure (a bit rusty), that if you use the “duplicate” function of darktable to generate multiple exposure-shifted versions of an image, you can select them all and feed them to the enfuse lua script without ever leaving darktable. It’s a bit slower and clunkier than the exposure fusion module being worked on, but it should do the job in a release version of darktable.

I will look be checking out for videos on this subject from youTubers :slight_smile:


I tried “exclusive and inverted.”. It was random try and gave similar output.

At present my knowledge about EQU is zero. At sometime I have to dedicate some time to digest this module.

I have tried Enfuse in the past. I had to install Lua script to make it work. Enfuse plugin got removed when I reinstalled OS.

I forgot about blending in BaseCurve. Thanks for reminding this. I will try this. Biggest advantage of this method is that it is easy to use. I will look forward to this in next version.

Thanks for summary.

I am very bad at explaining the mathematics behind these modes but, in the future, I might show a few examples of some of the blend modes often used in darktable.

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Some of them are explained here: https://docs.gimp.org/2.8/en/gimp-concepts-layer-modes.html (maths included :wink: )

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Thanks Daniel, I will go through it.

I really think you need to use drawn mask, as the foreground is not always separable using pixel values as selected by the parametric masks. I like to use drawn masks to roughly select the foreground area first, then refine with parametric.