Hey, how do you choose the right color profile in Gimp?
My lab says: “Please use only files without special ICC color profiles in the sRGB color space!
Please remove special ICC color profiles from your image files with an image editing program of your choice and save your images without embedded color profiles in the sRGB color space”.
My work process is: develop photos with RawTherapee, then open them with Gimp and finally export them as Jpeg to send them to the lab.
Which setting should I choose in Gimp?
The lab says that because they don’t want to deal with colour profiles. So,
1 Even if you embed one, as you should, they will trim the profile along with the metadata. That is okay because sRGB is the standard assumed colour space.
2 The longer answer is that there are many sRGB profiles out there. I believe GIMP and RT have reliable, well-behaved ones, though slightly different, so do not worry. Chances are there will be slight variation due to paper, ink and their devices’ software, etc., but that is to be expected.
Hallo afre,
don’t worry, that sounds wonderful. Thank you so much. Gimp 2.10.20 has problems with the RTv4_sRGB - a bug of the lmcs2 in Gimp. So I started to work on the profiles. This caused me a lot of stress, because I don’t understand almost nothing about it - my head is still smoking. I urgently need clarity and simple instructions that meet “normal” standards.
And now once again to the profiles:
On my monitor I never see a difference, which profile I choose in RT for export. When I open the image of RT in Gimp, I don’t see any difference if I keep the profile of RT or if Gimp uses its own. There was a lot of discussion in the forum about what to recommend. RT experts say: keep the RT profile. Gimp says: let Gimp convert to its own. Do you know if it really makes a difference? And does anyone know what Gimp does when converting? Does it always come out the same, no matter in which profile RT (RTv4_sRGB or any other) has exported?
In short: I need a good but simple solution. Which Jpeg will cause less problems later: The ones where Gimp took RTv4_sRGB or the ones where it generated its own?
I really hope that I don’t annoy anybody with these questions.
Hello micha, I set the output profile in RT/ART to the printer/ink/paper profile that I want to use. To see the differences between the profiles, you need to switch on soft-proofing (at the bottom of your screen, but read the tooltip carefully). If you switch on the ‘Highlight pixels with out of gamut colors’ option, the differences become more evident.
The same applies to Gimp, you must apply an output profile and activate soft-proofing.
I don’t think you can see any differences between RT’s RT4_sRGB and Gimp’s own sRGB profile.
To come back to your first question, I would just use Gimp’s internal sRGB profile. Your lab possibly uses their own printing profiles. What they ask is ‘do not use any color management system’ nor profiles. Just plain old sRGB.
@micha Let me elaborate on what I said earlier. sRGB is assumed when a profile isn’t available or removed. An example of it being removed regularly is on social media sites because they don’t want the metadata, which includes preview images, colour profiles and photo info, to take up space, and they want to eliminate the risk of there being malicious code embedded within the file.
What does this mean?
As long as you are exporting in a sRGB space you are worry free. GIMP and RT have good sRGB profiles. GIMP asks you on import out of courtesy and to teach users to take colour management seriously. Since the differences between GIMP and RT sRGBs are negligible, it doesn’t matter if you keep the input profile or convert to the builtin one. Personally, I would “keep” because I don’t want to risk creating artifacts (shifts, discontinuity or clipping) from converting too many times.
What I said about the lab is also relevant. If they don’t care to accept a colour profile, chances are that they don’t really care or aren’t knowledgeable about colour integrity. So, whether you convert or not, your influence on colour shift or clipping is smaller than their disregard for colour management.
Hope this helps.
PS
It won’t hurt for you to ask what they mean by sRGB and if they are willing to provide their sRGB profile. If they do provide one, then you could do the soft proofing that @paulmatth talked about. This would be an opportunity for you to learn their process and get to know them a bit more. If they are nice, they would be willing to talk to the customer.
Thank you both very much.
Let me get this right: RT and Gimp make good color profiles, so it almost doesn’t matter which one I use, and it also doesn’t matter if I keep the one from RT or let Gimp convert it into its own. Good.
But more critical is the color profile embedded in the Jpeg at the end. If the lab doesn’t know what to do with it and simply ignores it, I’m lucky at best, but it could also be that the exposure results in wrong tonal values and I don’t know why (at first).
This is how I understood you.
The idea to work with the profile from the lab sounds interesting. But I often do not know in advance which lab I will use for which photos.
Question: Is it enough not to confuse the lab by saving the jpeg without color profile when finally exporting Gimp? Or should I select the profile “No ICM: sRGB output” already when exporting RT? What do you think?
you mean not exporting the jpeg without a color profile? Okay, sRGB, but which one? I ask, mainly because labs says not to use any special one.
Do you think that’s a good idea to use “No ICM: sRGB output” in RT?
I have already answered the question in my 2 posts. Let me make it even clearer.
1 It is good practice to include a profile regardless of what you do with the files. The lab or social media site may trim that info but that is up to them because you are using their services.
2 In this case, including a sRGB profile or not doesn’t matter. It won’t have any bearing on their result since they treat the file as if it doesn’t have one or they apply their own without conversion.
3 What matters is that it is in sRGB colour space. The specific profile might be slightly different but GIMP and RT’s are both dependable. Cross your fingers that the lab’s is good too.
Which is why it is best to talk to the labs and figure out which ones actually care. Even if they aren’t knowledgeable, caring is one step toward a good relationship and good results.
This can only be true, if the embedded profile does nothing to the pixel values.
As far as I understand colour management, if there is no difference between with and without embedded profile, the profile must be trivial, i.e. it should not change the pixel values, i.e. the pixel values are already in sRGB-space.
Micha, take a practical approach. Take the same jpg, apply one time Gimp’s sRGB and save it, apply Rt’s sRGB and save again, mark one with G, the other with RT and send them to your lab. Then compare the results.
A poor man’s color management : if the resulting prints are too dark, adjust the brightness of your monitor to that same darkness level so that the lab’s prints equal that what you see on your screen. Same with contrast and RGB colors. Take a note of these values.
Next time you send a series of photos to that (same) lab, first adjust your monitor to those settings, then edit your photos and send them. I’ve done this for years with good results. No profiles needed at all !
Hallo paulmatthijsse,
oh, thank you very much. This approach seems very practicable for me. And so I can find peace and concentrate more on the artistic field of photography again. Yes, I will order prints with RTs and with Gimps profiles, also one where Gimp exports the Jpeg without color profile. I am curious. And of course I will report.
But I’m still interested to know what Gimp does when it converts the image into its own profile. Does the profile that RT exported before still play a role then? Or does Gimp make the same sRGB from all RT profiles?
The profile embedded in the image file is supposed to represent the colorspace and tone of the image. In that regard, it’s metadata about the image. When GIMP converts the input image to its preferred profile, it is using the embedded profile as the starting point for the conversion. After that conversion, the image is in the GIMP profile’s colorspace from then on, with that GIMP profile attached. If you were to say no to that conversion, GIMP would simply load the image as-is, and drag along the embedded profile with it.
In any event, the important thing is that the profile representing the image tone and color needs to be associated with the image. So, either answer is really okay, as long as the correct profile stays with the image.
Let’s make it a simple analogy. Say this year my dog is 10 years old. Mr Shakes is in fact 10. You wouldn’t know he is unless I tell you his age. You also wouldn’t know when he’ll turn 11 unless I tell you his birthday. In the same way the colour profile you export with tells you what the RGB 0-255 values mean.
Now if you open the image in another app, or RT again for that matter, it would know a little about the image given by its metadata tags and binaries.
GIMP takes it one step further and offers to change the colour space to its builtin one. Why? Because it knows its profile is robust and good for editing. RT’s is good too but GIMP doesn’t know whether that is true or not, just that its own is reliable. Hence forcing the question on the user.
On conversion, it transforms from one profile to another. You need 2+ profiles to do this. An analogy would be like changing miles to kilometres. You need to know the value and the units before you can do a conversion.
Which brings me to @Jossie’s well meaning comment.
A profile in itself doesn’t change values per se. As I said above, it defines what the values mean. So trimming, ignoring the original profile or assigning another profile won’t change the actual values. However the assumed or assigned profile would redefine what those values mean. (Of course, there are other considerations to be made such as intent, gamut and gamma compression or expansion.)
In conclusion
Without cooperating with the printer (lab), there is absolutely no way to control the colours if they explicitly state that they aren’t interested in colour profiles. By using their service, you waive that right.
You could definitely test their black box (unknown) process by doing a dozen test prints as @paulmatthijsse suggested. I would advise to do this even if the printer does excellent colour management because the result will always be different from your expectations. Better labs would even be willing to do test prints for free. It just depends on the printer you are willing to work with.
PS I made lots of fast edits to the post, so if you were reading within 6 min things probably changed quite a bit. One thing I would caution about is that some printers will automatically edit your photos via enhancement algorithms or manual curves, which would definitely change the colour. This is worse than ignoring your profiles. One more reason to make test prints if you are printing something important.
I guess the heat took its toll from me yesterday evening …
You are absolutely correct, embedding a profile does not change the pixel values. Only transformation to another colour space does. If no profile is embedded the lab will assume the image is in sRGB, most likely the standard one. So the result with sRGB embedded and without an embedded profile will be (almost) the same. I say almost, because there are different versions of sRGB around.
The profile provides the recipe how to convert the RGB-pixel values in the image file to the profile connection space (PCS). Using it, an application like GIMP can convert to another colour space, display it on the monitor (using the monitor’s ICC-profile) or print it (using the printer’s ICC profile) resulting in the correct, device independent colours.
Hallo afre,
I am overwhelmed by your detailed, very well understandable and lovingly described explanations. Many thanks also for your patience with my slow understanding.
Yes, the most important thing is to switch off the automatic image enhancements of the lab. I was even lucky that I could always call my lab to switch off the normally always on re-sharpening, extra. Unfortunately, the lab was dissolved, and the successor makes terribly bad (extremely resharpened photos).
Another laboratory, now available for selection (saal-digital) says I should use the profile: "sRGB IEC61966-2.1"
Which profile should I choose in Gimp, and which one before in RT, to get that profile in the final Jpeg?
micha
Hello, the following article might clarify some of the concepts of colour management. It is written by Neil Barstow and talks about icc profiles, device-independant working spaces, converting between color spaces, Lab, XYZ and more. It helped me to understand a bit more this wonderful (complicated) world of colour management…
