Running Windows 10 64 bit, gimp-2.10.18, and gmic_2.9.0_gimp2.10_win64.
I think the contrast I see in the G’MIC preview has more contrast than what I see when I view the resultant image in GIMP.
G’MIC
GIMP
G’MIC
GIMP
I have also seen other, greater differences between the images in G’MIC and GIMP. Is this typical? Can it be changed?
I noticed contrast are different with Krita on 16F RGBA and my test with attractor fractal. This isn’t just a GIMP issue.
I have two explanations for this.
1 The plugin preview is inaccurate because its render does not have the same properties of the original image, whether by the number of pixels, precision or colour space. The preview image being processed isn’t the same as the input image!
2 If you remove the GUI level of abstraction, the CLI still won’t display the image the same way because of the last two reasons above and its rendering engine is different. E.g., I find that Firefox renders the same image considerably softer and smoother.
Thus, I always save or apply the process and then view the image in the native environment or medium where I would continue the editing or do the sharing.
Here are two images:
G’MIC preview
GIMP
Only operation applied to it was G’MIC >Colors > Mixer [PCA]:
The original image is test.dc-lx100m2.015.rw2 and comes from Shades of brown
It was opened in dt, the base curve removed, and then exported as a 32 bit tif. It was opened in GIMP as 32fp linear light and with the GIMP sRGB.
What I find is that I will have to over-process in G’MIC, guessing by how much, and then see what it looks like in GIMP. Correct by resetting, if necessary, and then repeating until I get what I want. Rather difficult and time-consuming. I am just discovering what G’MIC can do, and I like it, but I would not use it much if this is the routine.
Another explanation : are you using a .icc color profile ?
G’MIC does not apply the color profile when previewing filters.
Here’s how GIMP is set:
So yes, there is a .icc profile used.
I would say this is probably what explains the difference between the preview and the final result
G’MIC preview is not “color-managed” for the moment.
What do I change?
The Soft-proofing profile should be None. I don’t say this is the problem, but this may be a part of it. Needs testing of course.
I changed everything one at a time to end up with this, but w/o improvement:
@iarga
I was trying to reproduce your recipe for Shades of Brown and ran into this problem. Perhaps you would comment on whether you see this.
I used GIMP 2.8 here. Therefore no color management. I use G’MIC preview as guidance. After G’MIC “Ok”, I view the result in GIMP. If the result isn’t nice I redo the G’MIC filter with different settings.
Side note: the grainy result is normal after strong PCA settings, therefore I used Wavelet Denoise right after Mixer [PCA].
I used this:
first
[G’MIC] Pyramid Processing: iain_pyramid_processing 6,12.09,0.267,0,2
then
[G’MIC] Mixer [PCA]: fx_mix_pca 0.174,-5.1,0,-0.6,-0.219,11.22,0,76.6,-0.219,5.1,-1.8,77.8,1,-1,-1,-1,-1,0,0,0,0,0,0,0,0,0,0,0,0,0,50,50 (first twelve values of this list)
Thanks. You’re a patient man. At least I know I am not alone in having to do that.
Is this right?
This is how it came out in GIMP. Interestingly, this is more saturated (to my untrained eye) than the preview.
One of your Mixer [PCA] values is not the same. secondary factor must be (negative) -0.219
edit: I tried +0.219 and got the same result as you, so this gives the difference!
What did you use before the Mixer?
I used RawTherapee neutral
I only used it as a raw converter
In GIMP 2.8 I converted this to RGB working space (sRGB built-in)
then Pyramid Processing with the above values
then Mixer [PCA] with the above values
I fixed the Mixer. I hadn’t been using the Pyramid Processor because I was just focused on the change in appearance between G’MIC and GIMP. So now I have put it in. I am guessing that this is correct for the last two: 0, 2.
I ended up in GIMP with this:
and
compared to this in G’MIC
I think I have eliminated color management in GIMP. So this is a bit of a mystery. Something I could learn to live with, though.
This is correct. I like the end result in GIMP. This is the way I used these filters.
I can’t help you with the difference in preview G’MIC and GIMP. I will look into this another time for myself. (in a few days)
I don’t think it is a good idea to turn off colour management, and I would only use soft-proofing as needed (i.e., not on by default).
Personally, I would disable the plugin preview and click on apply to see the result on the GIMP canvas. Undo and reapply as needed. Better than wasting time with the preview.
Another tip is, if processing is too long for the more sophisticated filter, try using the selection tool to make a rectangular selection of the image. G’MIC will operate on the sub-image. While the stats of the sub-image won’t be the same as the whole image, at least you get a quick idea what the filter does with a given set of parameter values.
I turned it back on, and I think it took a very small amount of red out of the image, not nearly enough to be concerned about. Since AFAIK the only way to find out what the sliders do is to play with them, I need preview. I just have to accept that what I see and what I will get will be two different things. Learning how to manage that will be trial and error.
Fortunately, I have enough power that computation is not often a concern.
I have worked with G’MIC enough to get used to, or maybe better put, ignore the differences. I have managed to produce this garish version of iarga’s version of the leaves. A person could spend a long time learning how to use the G’MIC tools to produce what he wants. My development was:
G’MIC >Details > Pyramid Processing (iarga settings)
G’MIC >Colors > Mixer [PCA] (iarga settings)
GIMP > Wavelet Denoise (CbCr)
G’MIC >Details > DCP Dehaze
G’MIC >Colors > Mixer [PCA] To get additional redness
GIMP > Wavelet Denoise (CbCr)
G’MIC>Degradations>Blur [Gaussian]
Definitely garish! Glad you are more comfortable with it now. 
