Thanks to everyone.
Lots of opinions on the color of the sky. I can assure you that the sky can be blue in Denmark, but the color is very much depending on the angle to the sun and other factors.
My original problem/question falls in two parts:
How to change (edit) the color of the sky (maybe change it to almost white) using darktable preferably without a mask and avoiding halos at the border between the sky and other objects or changing the color of all other objects as well.
Having read all answers, I conclude that without a mask only relatively limited color changes are possible in Darktable.
Now for the other part:
The Iphone shot looks unrealistic. The image has not been edited in any way apart from the Iphones build in jpg conversion, so the result is what the Apple engineers think that the customer likes the most.
Reading magazines (photo, nature, wildlife etc.) we all get accustomed to colourful, sharp and high contrast images. The sky is often very dark blue. It looks amazing, but the images are not realistic. I admit that I tend to edit my photos to achieve this kind of look as well.
Is this look only the result of editing (in-camera jpg or post production) or is the dark blue look also build into the hardware of the camera i.e. the sensor?
I am not sure these all can be done all at once…
You can try to reduce the saturation of the blue colour and raise its luminosity. The are more modules that can do this in darktable, so try and see which Briggs you the result you want.
Just worked on the sky, except for a little work on the statues to touch up what my other work changed. @obe: Are you saying the sky really was nearly white, but the camera produced dark blue?
Yes I do. I think that my camera has a tendency to produce skies too dark blue. A pale blue sky is how I remember the scene. More like the sky in the photo below……
I am going to be picky, but if you use raw, what is out put by camera are the data as produced by the sensor in the camera space. Only when a camera profile is applied that we can speak of colors (blue…).
So it may happen that the camera profile you use is not good for those landscape photo. The first step seems to me to be sure the camera input profile is ok.
Regarding color of sky, in your photo, the sky is largely underexposed due to foreground very luminous white subject and will necessarily appears dark blue without specific correction.
I should add that the thickness of athmosphere passed through by light is very important : sky is darkening with altitude;
there is a very strong gradient from vertical sightseing to horizontal.
I shot the photo in raw and used the standard color matrix supplied by darktable. Scrolling down the available profiles no one seems to produce a better result.
It’s correct that the photo is underexposed (to avoid clipping the white figures) but adjusting the exposure in darktable should compensate for that and bring back the correct blue in the sky.
When I look at the pictures shot with my wife’s Iphone – no editing outside the camera – the skies are much more dark blue than in real life. It looks nice, colourful and dramatic but it is not realistic. We have become used to colourful, highly contrasted and very sharp images. Real life has become dull…
The actual color of the sky depends heavily on time of day and the atmospheric composition at your location at the time of the photograph. See e.g. here for Granada, Spain, here for Ontario, Canada and here for New Delhi, India. The presence of scattering particles in either upper or lower atmosphere, and the presence of ozone can also influence the color spectrum.
So blue, isn’t blue, isn’t blue
Though I agree that the iPhone doesn’t seem to aim for accurate color reproduction…
DSC_2122.NEF.xmp (14.1 KB, dt3.3)
What I found ‘unnatural’ in the first image was the dark sky at the upper border. Therefore I applied a gradient mask and used the exposure module to make the upper part brighter.
This is the decisive factor. The optical (physical) phenomenon behind this is Rayleigh scattering. It depends on the number and the radius of scattering particals and the wavelength. Rayleight scattering is inversely proportional to the fourth power of the wavelength. This means that short wavelength (blue, violett) scatter much more than long wavelength (red). Our sky looks blue.
Depending on the atmospheric conditions this can lead to extreme situations. I remember a very cold winter day (about -30°C, extremely low temperatur of dew point) at an altitude of about 4000 m were the sky looked extremely dark blue (nearly black) looking upwards in a nearly vertical direction.
