What is your technique to greatly darken the sky?


(Hardy Wang) #1

Let’s say I have this picture https://www.dropbox.com/s/i4syjw703nmfdmn/DSC_0925.NEF?dl=0 the sky in the background is too bright. I would like to make it much dark to be more dramatic just like storm is coming, meanwhile keep the foreground church bright enough with good contrast.

I tried 2 solutions so far, but not satisfying yet.

  • I added a graduated density filter to cover sky and push density to some high value. The sky is darkened but the church tower and body parts have different lightness now. It is a bit tricky to bring them to the same brightness.
  • I used 2 exposure modules and luminosity mask in each. The first exposure module’s luminosity mask targets sky, and I lower the exposure. The second exposure module’s luminosity mask targets anything other than sky, and I increase the exposure. But the consequence is that the halo around church tower becomes very ugly, and the trees on right side of the picture has strong fringe developed. But at least the church tower and body are same in terms of brightness.

I run out of idea in darktable, what can I do to darken sky and still make it seamless?


@hardywang See Deep blue sky effect for inspiration.

(Hardy Wang) #3

Thanks, but it does look a bit different because what they did is to play with blue color. However my sky is total cloudy, no blue color.


In Darktable:

  1. Remove base curve
  2. Duplicate 2 times
  3. Exposure: Original 0, First Duplicate +2, Second Duplicate -2
  4. These 3 pictures are merged with enfuse_pro_2 filter> Tif-picture
  5. Open Tif to darktable, adjust (DSC_0925_01-03.tif.xmp (3.0 KB)), export jpg.

(Andreas Schneider) #5

Reduce the exposure and use a lowpass filter.

DSC_0925.NEF.xmp (8.4 KB)

(Boris Hajdukovic) #6

Hi @hardywang!

I don’t think that in this case it is easy to darken the sky because the brightness and color differences between the sky and the rest of the image are not very high.

I got fairly good results with the combination of darktable and GIMP:

In darktable, first I applied parametric mask to the sky and lowered the exposure:

By the way, @houz and other darktable developers, is it possible to copy the parametric mask from one module and apply it to another?
I know that you can reuse existing shapes, but it would be nice to be able reuse parametric masks as well!

Then I reduced the dynamic range of the image with the help of low pass filter module:

Here is xmp file: DSC_0925.NEF.xmp (2,3 KB)

In GIMP I used more luminance masks to further darken the sky and increase the contrast of the image. At the end applied high pass filter to sharpen the image:

Here is the final result:

The main problem with this picture is that the light source is behind the church and any darkening of the sky without the rest of the picture feels unnatural because of very diffuse light reflection of the church. When the light source is in front of the object, a dramatic sky looks much better. Here’s an example of mine:

(Shreedhar Inamdar) #7

This looks realistic to me. What do you think?

DSC_0925.jpg.out.pp3 (12.2 KB)

Basically used the Residual image module of the Wavelet Tab to reduce highlights. That made sky dark. Used a bit of LH module of LAB to darken it just a bit more. Then used Defringe to remove blue fringing on the cross. Used the tone curve in Exposure module to introduce a bit of contrast. Lastly, CH module of LAB to make sky bluer.

Edit: Sorry, I just realised that you want a solution with darktable. I used RawTherapee. Anyways, you can see it as an alternative.

(darix) #8

This article comes to mind

(Thomas) #9

Just three modules in darktable: Haze removal for the contrast of the church, a tone curve with L-channel mask for the sky and a second tone curve for the general appearance.

DSC_0925.NEF.xmp (5.5 KB)

(Mica) #10

You can use the same slider values, but you won’t get the same luminosity mask for the 2nd use, since the first use is modifying histogram.

(Christian Kanzian) #11
  • I limited the basecurve with a parametric mask to the shadow parts.
  • A second instance of the basecurve with exposure fusion and approx. the same mask to push the colors of the shadow parts.
  • Shadows and highlights modul to bring down the hightlights
  • local contrast

Well there are some halos around the clock tower, which might be disturbing :disappointed_relieved:

DSC_0925.NEF.xmp (4.4 KB)

(Boris Hajdukovic) #12

Yes, but it would be great if you could somehow save the “snapshot” of the mask itself that you made with one module (not the values of the slider) and use that mask again later.

In GIMP, you can make a quick luminosity mask (which is similar to parametric mask in darktable if you select a certain brightness range with the help of slider):

select it (alpha to selection on that layer):

and save selection as channel (Menu “select” - save to channel):


Now you can use this mask for further editing:


(Mica) #13

You can reuse drawn mask objects.

Gimp has some awesome features, and the making is among them :slight_smile:

(Thomas) #14

You could make the halos an artistic feature :wink: . It’s a church, so some mysterious light might be be adequate.
Just two modules: base curve und exposure in darktable :sunglasses:.

DSC_0925.NEF.xmp (2.0 KB


The technique should still work since we are drawing contrast from the Red channel, which happens to have more contrast than the Blue one in your image. I wrote a G’MIC filter (Darken Sky) that you could try in GIMP if you are interested. It isn’t a carbon copy of the tutorial but people have told me that it works nicely.

The default setting yields passable results. There is blurring at the inner corners of the cross. That might be due to the fact that I resized the image prior to applying the filter or something else… but not something that could not be rectified. The colour might need some fixing as well; the point is that there is a lot that you could do to improve the contrast.


In terms of masking, I don’t think that people have mentioned this (much) or maybe it isn’t obvious, but you could do the luminosity masking technique on channels that have nothing to do with brightness.

In general, I would examine various channels to see where I could gather information that could be manipulated or used to improve the image. Take a look:


(Hardy Wang) #16

Thanks everyone, very informative. I learnt some tricks, such as HDR stacking. And @afre I will look into the article again. @s7habo great to remind me of the light source and background color issue I have.

(Roger) #17

Think as photographer!
What is the problem? You want the exposition in the back to be a few steps of light below.

  1. Make a mask in the sky.
  2. Reduce the exposition and increase the black as you want:
  3. Enjoy.

(Christian Kanzian) #18

Parametric or drawn mask?

Metadata of the JPG has been striped.
Please provide the xmp file, so that one can repeat the steps.


Three pass of shadow/highlight tool with high radius and bilateral filtering and some curves (auto scaling in rgb)

DSC_0925.NEF.xmp (84.4 KB)

add one curve for brightening the midtones

(Roger) #20

The Base mask is enough because you do not need to make further contrast adjustments, but actually, any masking with any software (including Gimp) work because you are just splitting the image into two, one with Exposure 0 and a second with Exposure -N.

I have no files, they are deleted, it was just a few seconds dummy to show how the sky is easily darkened.

However you will note a different tint, this is because I adjusted the white balance, please forgive it, it is a photographer habit. I did not know if the church was white or not, so I took the small monument on the left as reference.