I have a question about color management. I would be very glad if you can explain this behaivour.
I exported a file with darktable using sRGB as output color profile. When I open it in digikam and I enable color management with sRGB as working color space, some reds differ from the original image.
Without color management, the image looks the same as in darktable.
I suppose this behaviour has something to do with the working color space. But why is a working color space needed when displaying an image if the image (I suppose) already embeddeds the sRBG color space?
It means that the sRGB color space of darktable is different as the sRGB color space that I select in digikam. How many different sRGB color spaces are there then?
Does somebody know where the darktable sRGB color space is stored and how can I import it in digikam?
I know I can just deactivate color management in digiKam, but I would like to further experiment with color spaces.
@RawConvert Maybe you could answer some of my questions? I saw that you were dealing with something similar here.
@7osema , I’m afraid I’ve never used digikam, so don’t understand your problem.
Quite a few! They come with different gammas and/or may be linear or not linear. There are V2 and V4 types reflecting changing approaches (I think). Some are just a matrix, some also have a look-up table (LUT). It’s complicated! Others more knowledgeable than me will have to explain!
Re. the ref. to the previous topic, as you see it was never established where dt get’s it’s standard profiles from. They don’t seem to be part of what you download when building dt, not obviously anyway. I’m using Ubuntu so did a Catfish search of “File System” for .icc. Whilst /usr/share/color/icc… seems a possibility, it doesn’t match up with the dt dropdown in Output Color Profile module. @priort , do you know? Or ask the devs on github.
There’s a standard for sRGB; compliant profiles need to use its primaries and tone curve: IEC 61966-2-1:1999
That said, there are a number of ways to skin the cat. While the primaries are intended to be used in a matrix multiplication, an equivalent transform can be coded in a LUT. The spec tone curve is the marriage of two separate equations meeting at a common point, but a simple exponent is usually used with no adverse effect.
If you want to mess around with various profiles, Elle Stone has a nice set here:
I believe the basic ones are or I was told at some point unbounded and I do think they are hardcoded and part of a DT install… I would have to dig to be sure…
But I am the farthest thing from anyone that should be considered a trusted resource on this topic…it is pretty complex at times.
EDIT:
From this quick search of the code …maybe created with code in colorspaces.c ?? And perhaps elsewhere…
At the end, my problem/question has nothing to do with digikam, but with the fact that there are several sRGB profiles with the same name.
So I try to reformulate the question: which working color profile should I use in a color managed image viewer(like digikam) to get the same color renditions as in darktable(being darktable output profile the default sRGB)?
@ggbutcher@priort thanks for your links. They are good to take a deeper look into this topic.
If DT output image with some sRGB profile of its own, it should be embedded in the output image. Then this DT profile could be used by digikam to render the same colors, as digikam is color managed
Yes that’s right. But the embedded color profile will be used only if color management is disabled in digikam. That was somehow confusing for me.
If you enable color management, you have to select a working color space that will be used to show and edit the images in digikam. This working color space can differ from the embeeded color space, thus showing different colors.
So at the end, I’m better off disabling color management in digikam. I think color management in digikam is useful when you edit there your pictures or you want to check how will they look with a specific device.
Hmmm, the working profile shouldn’t be used to actually show the image; the software should be converting to the display profile for that. You should never actually see an image in a working profile gamut or tone.
So it seems that digikam is using a calibrated monitor profile created with DisplayCAL to display images. (I calibrated/profiled my laptop screen because it seemed to be too reddish compared to other displays I have).
Then I checked the display profile used by darktable, being it sRGB (web-safe). If I select there system display profile, I see the same color rendition as in digikam.
Then, if I’m right (you can please correct me if I’m wrong), the problem was that I was using a wrong color profile to display the images in darktable (sRGB (web-safe)). If I use system display profile everything seems to be consistent. In other words: if I use the same display profile in darktable and in digikam I get the same color rendition. A rookie mistake
The complete objective of color management is for images to look close to the same on all display media. If that’s not happening, need to make sure all the pieces of the gonkulator are properly fed before indicting any one of them. The whole “working the image in sRGB” or some other rendition colorspace (see that a lot at DPReview) just indicates an incomplete understanding of the gonkulator… which is one of the many reasons I enjoy hanging out here.
