ASD00773.ARW (45.0 MB)
With some pictures I get a discrepancy in the saturation between normal preview and high qualitty processing preview. The same difference I get when I ouput to jpg.
If I don’t use the contrast equalizer, both pictures (preview, jpg) show the same saturation.
Similar or equal saturations I get by the (non scenic) “local contrast” module, or if I increase contrast using “diffuse or sharpen”.
Problems with contrast equalizer seem to show up especially if the picture has small sized details like grass or moss. However, the majority of my pictures is OK.
I attach a typical file for the demonstration of the described problem.
File ASD00773 is own work and licensed [CC0] (Creative Commons)
darktable sacrifices some accuracy for speed during editing. The high quality processing was implemented so that users could get the accurate view of the processing. The penalty for the accurate view is a sacrifice of speed.
I’m not 100% certain this is technically correct but it is what I observe:
Contrast equalizer (and local contrast) tend to relatively desaturate the edges they brighten/darken by only affecting the luminosity, not the saturation (except when you also tune up the equalizers chroma tab).
In an image with lots of fine details this effect might not be visible in the regular preview because the finest details are flattened by the lower resolution of the preview.
Using the high quality preview allows one to accurately assess the actual effect.
Diffuse or sharpen is even worse in my experience, not so much on the colours but affecting brightness much more on the output then the preview shows.
I downloaded and opened your image with your xmp file. I can confirm that high quality processing changes the look of this image. I wonder if high quality processing is disabled in the export module if this would resolve the issue for you. I am presuming you have high quality processing enabled in the export module.
I just tested your image and if high quality resampling is set to no in the export module your problem is resolved. When it is set to yes it produces a darker JPG. So your export settings need to match your processing settings.
This has come up a few times before. Searching the forum will provide you more discussion but basically you can see the esp with certain modules…dehaze is another one that the downsampled preview when zoomed out away from 100 percent will often look quite different than the preview using the full image data…it will often look more contrasted and or appear to have more detail at times as well…
Not sure how to make this more evident to new users…
@roberthoell, have you tried exporting to a image with the tiff format? Apart from the already mentioned reason, also the jpg compression can have an impact. I have sometimes the same issue, and jpg is often the culprit.
I always applied high quality resampling set to no in export to jpg. For the number of pixels I did not change the default 0,0. I used 2000,2000 as in your screenshot and the saturation problem has been really solved, but reduces the resolution as could be noticed when zooming and comparing this with export size 0,0
You might want to just set the long side to what you want so you keep the aspect ratio of your photo.
No as a setting for hqr will be the best match for the default preview but it can often be worth while at least for images you care about to check the high quality preview and then to export with hqr set to yes so that the output matches…
Often there are halos or micro halos on details and other artifacts that you will notice and maybe even trying to edit them out and in some cases simply using hqr would remove them…
I will see if I can find a good example just to show you what I mean …
