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I have some images and I need to print them with faithful colors.

Each image contain a full color target or part of it (I am using X-Rite "ColorChecker Passport Photo").

I did not shot in raw, the images are jpg.

I have a look at the titles of these video tutorial but I do not know where to start...

-Applying DNG profiles in Adobe Bridge & Camera RAW

-Applying DNG profiles in Adobe Lightroom

-Creating & Using DNG Profiles with the X-Rite Mini ColorChecker

-DNG File Format Advantages & Importing Into Adobe® Bridge

-DNG File Format Advantages & Importing Photos into Adobe Lightroom as DNG files

-Lightroom Application - Plugin Is Not There

-Using the X-Rite DNG Profile Manager Utility

My idea is that I can apply some kind of image processing in order to transform the colors of my images into the "expected" colors listed here: https://xritephoto.com/documents/literature/en/ColorData-1p_EN.pdfenter image description here

and then I will have an image ready to the printer? Or no?

My approach, the following is the original image enter image description here and the following is the result after applying a linear transformation (3x3 matrix) to each pixel color. The 3x3 matrix is the least squares solution of the linear system which equates the sampled median color to the nominal colors found a x-rite site. enter image description here

  • The "Learning" tab at the top of the site link is a good place to start. It begins with "Why calibrate" and "How to profile." – Stan Oct 14 '17 at 14:53
  • All the tutorial you have mentioned deal with DNG, but you shot in jpg, so none of them will likely help you. You need to start by shooting in raw for any of these to be applicable. – Robin Oct 16 '17 at 13:42
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Unfortunately, by shooting the images in jpeg your camera has applied non-linear processes to the image. It does this to produce more pleasing images but at the cost of distorting colors and tone. This process is called an "ouput referred" transform. This link discusses this process and why it is done:

http://www.color.org/icc_white_paper_20_digital_photography_color_management_basics.pdf

In order to get colors to closely match a colorchecker you need to do what is called "scene referred" processing. While rare in normal photography, it's used extensively in reproduction work where you are trying to create the best copy of an existing artwork or photograph. This is always done using RAW mode with special converters designed for scene referred processing. It's imperfect because the color filter arrays have a somewhat different spectral response than human vision but it's a lot better than using the standard "output referred" processing and can make quite good copies. One way to see how much distortion occurs in standard output referred photography is to take a picture of a picture then white balance and print it. The differences are stark.

OTOH, if you process an regular photo image using scene referred techniques and print it you will normally find the print unappealing. So that's why it's a technique only used in scientific applications or reproduction work.

Getting back to your issue having only jpegs to work with one approach that will require some work is to apply inverse curves in Photoshop that reverse the "S" curve typically applied when the jpeg is created. Determining that is non-trivial but one approach is to print a series of patches from RGB (0,0,0) to (255,255,255) in small increments. Then print this using a good inkjet and paper that provides ICC profiles for that paper. Do this using Relative Colorimetric Intent (see Photoshop's help). Then take a jpeg picture of that together with a colorchecker using your camera using the same settings used in your other pictures. You should then be able to use the info panel to adjust with a curves layer the values so that each patch comes out close to the RGB levels you used to create the print. Once you have that curves layer you can save it and apply it to the other photos to reverse the jpeg tone changes.

Afterwards you may still need to adjust saturation as it's common to increase saturation somewhat in output referred photos. But first fix the tone curves.

Sorry, but this is a tedious process but I'm not aware of any simpler approach. Further, do not expect a print of your image to look very good. They normally appear more washed out that what you are used to which is why photographers don't use scene referred processing outside of specialized fields.

There is a considerable amount of detailed information on color and how it is handled by printers and cameras at www.color.org should you go down this path and need more info.

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