I have a series of pictures they have the same unicolor background. My goal is that on all pictures the background has almost the same color and brightness.
For that purpose I used color calibration module and created a preset after calibration with a color checker. I took a picture of Datacolor Spyder Checkr in the beginning and at the end of the shooting period.
I matched first the brightness of the background via color picker (L channel of Lab) and then I used the preset I stored from the picture of Datacolor Spyder Checkr. The white balance of the camera was not “auto”. I set “daylight” as WB in the camera for all pictures.
This procedure did not work well. There are still some color deviations of the background among pictures. The brightness plays also an important role.
Another possibility would be to copy and paste certain settings via history stack from one image to another. Actually, I need to transfer the RGB values and the brightness of the background picking them from one picture with well adapted background color to all other pictures.
auto exposure doesn’t give always the same exposure even in the same lighting situation. You don’t know how the algo in the camera is reacting on smallest changes in the scene.
So if you want to have equal conditions it’s highly recommended to use manual mode
Use an analysis of the image’s histogram to automatically set the exposure. Darktable automatically selects the exposure compensation that is required to shift the selected percentile to the selected target level (see definitions below). This mode is particularly useful for automatically altering a large number of images to have the same exposure. A typical use case of automatic mode is deflickering of time-lapse photographs.
automatic exposure in darktable doesn’t compensate the behaviour of the camera. You need to control the whole process chain from scene lighting over camera exposure to raw processing if you want to get the same output.
Thats is fine but what would you do to answer the OP’s original question. Of course we would control all this in a perfect world but given a situation with some variation what steps would you suggest to attempt to correct or equalize things as requested??
There’s no automagic way for this in darktable. If the lighting isn’t controlled then there‘s no short track avoiding manual tweaking using color picker and color calibration or colorbalance
Got it so you are suggesting it has to be done photo by photo manually. I know LR has some feature to automate this I have no idea if it works at all. From the description I thought auto in DT might balance images if at least they were close by setting them to balance the histogram based on a set point for the median pixel values …what you say makes sense …
Thank you for your feedback, Todd and Martin. As Martin pointed out, it is a tricky and tedious work to match the colors and brightness of a series of images. I attached two examples as JPG that I processed so far. They look good. But, if you print them on the same printer, you notice a difference. The picture with round black button looks greenish, the other one more natural and neutral.
The pictures were taken groupwise under homogen and natural light with a reflector. The color of the background as you see is very soft and it is not 100% gray tone.
To set the brightness of the background worked well with the color picker in the Lab space using L value. This was also a manual work. I modified the exposure until the L value in % is almost the same on the background of each picture.
The problem is with the absolute RGB values. They also depend on the brightness.
