I own a Pentax K-1 which is set to saving the pics as DNG and currently use Darktable 4.2.1 under Debian bookworm Linux. In the last time I did several experiments with high key photography, i.e. used a set-up with white background and exposed, sometimes overexposed to the right side of the histogram. When importing the photos into darktable the preview always looks good, resembling the pic of live view monitor. But when opening the photos in the dark chamber, they are underexposed and quite dark. I always have to increase exposure to quite an extend.
By selecting each automatic step one by one from bottom to top, I tried to identify the module that may cause the problem, but couldn’t find anything.
What may be the problem? Somehow it seems that the raw data are not correctly interpreted …
Should I change to Pentax raw format? I use DNG only, because it wasn’t supported at the time I started working with raw.
There is no problem. Your camera, and, by default, the preview in the lighttable, shows a processed JPG created and embedded by the camera.
If you did not shoot in manual mode, but used exposure compensation, darktable’s exposure module will, by default, undo it (it assumes you used ETTR to maximise the signal-to-noise ratio, and tries to restore what it thinks it’s the correct exposure). There’s a setting in the exposure module to disable that.
Even with that option disabled, you may have to add a bit more exposure in that module (some brands/models require 1EV extra, or even more).
In general, you’ll have to work a bit to get something close to the camera-generated jpeg. But once you learn how, you can often do better than the camera (that’s the whole reason to do raw processing in the first place!).
Best thing is to have a good look at the manual (especially the first few parts, then the module reference when needed). There are also tutorials on e.g. youtube. Do be careful with tutorials made with or for other programs, as darktable works in a way that’s quite different from most other programs.
Also, using high-key images to learn processing with darktable may not be the easiest way. Perhaps start with some more “standard” images, where you have a good distribution of tones, from shadow, through midtones, to highlights.
Reason: the recommended workflow is:
set the brightness of the midtones with the exposure module
then adjust shadows and highlights with filmic or sigmoid.
If you start with an image where there are few midtones, the first step becomes more complicated…
Besides deactivating the exposure compensation and adjusting exposure perhaps a little as @kofa indicates, I would try / recommend as a first step to also deactivate filmic or sigmoid.
As you exposured to the right, there may be no need at all to fiddle with the tone mappers. Just my 2ct from my experience when handling high key in darktable.
Wish you much fun while processing, perhaps you like sharing one of your shots here? If you like others to show their rendition, you may share a RAW as a playraw in the forum.
Have a good time
The default behaviour of DT is to counterbalance the camera’s exposure compensation setting. In the screen grab here it is undoing a +1.7 EV setting in the camera. The developer of filmic determined that many cameras need a EV adjustment of +0.7 to match the jpg out of the camera, but this varies between cameras and at best is an educated guess. The solution for you is to make a preset or make a style that gives you the expected look with one click. I have styles that match the exposure as shot in camera or that counterbalance the camera’s EV compensation. The later works well for me because I travel a lot and take bracketed shots to ensure one exposure will be good to work with.
Actually, I have been working with darktable already quite a while, learning about it step-by.step. I was just stumbled by the even much more extreme outcome between screen view, embedded jpeg on one side and raw on the other side in the high key experiments,. “Normal” shots I am used to be underexposed to some extend.
It is a tradition of Debian stable to be slow including more recent software versions. Since the version gap was so large, I now installed darktable 4.8.1 as a flatpak. Thanks for the hint …
There are official appimage versions available. Some people had issues with flatpaks, due to the sandboxing flatpak enforces. The sandboxing doesn’t play nice as soon as you have to go outside the “normal” user directory.
And not only Debian is slow in updating to recent versions. In fact, I think most “fixed” distributions won’t include newer versions of software at all unless they have to correct security flaws. That’s why community repositories are so common and so useful.
finally it seems that I mastered most challenges (getting rid of shadows by lighting background, almost equal lighting of background by moving lights further back etc.)
If I run into problems with flatpak, I will try the AppImage. Currently it seems to run nicely. flatpak-spawn is new to me …
I add one of my experiments. The color of the background may still need some adjustment. It shows flower umbels of wild carrot, one already transforming to fruits.
