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I work for an institution with a large photographic archive of art, containing among other things colour negatives and ektachrome films. My team is digitizing the films and in the meantime we want to restore the colours as good as possible (the films have degraded in different degrees throughout the years).

Often a colour chart is photographed together with the piece of art, f.e. the Kodak Q13 or similar patches (example). Yet, I do not succeed in using these charts for a good colour restoration. I know the charts were intended for a good reproduction on print and not for digital restoration (see another question on this topic), but still, I really suspect that there is a way to use this information.

Software solutions for reading colour charts point me in the direction of camera or scanner calibration (f.e. Adobe DNG profile editor or Silverfast), but I do not find a way to use this to restore a colour photograph.

FYI: on this moment we do colour restoration in Photoshop, based on the 90% method, using the whites and blacks in the image and getting them right with the levels or curves tool. Sometimes this is enough, but sometimes it is not.

Any experience with this matter?

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Katrin Eismann wrote an excellent book called Photoshop Restauration and Retouching. It is full of excellent advice targeted to your problem. There is also short discussion of using reference color charts. Highly recommended.

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I cannot help you directly, but I can give you directions.

I also think it is possible to automate the procedure, especially if the color chart has the same shape everywhere, but it requires some programming.

An idea would be to load the X-Rite Passport plugin in Photoshop and try to use it to "calibrate" the image itself. However, you have fewer patches (9, excluding the grayscale) that he Macbeth colorchecker has (24), and the passport has a standard placement you also miss. I never used that plugin, so you should try yourself. If it doesn't work, try Imatest.

Another option is to write the correction algorithm yourself.

Said algorithm should first identify the patches (not so hard, it's a series of rectangles), create a CLUT, then apply the CLUT.

G'Mic is a tool that allows you to do so.

More links:

Try to ask in G'Mic, Darktable and Imagemagick forums/mailing lists. They will help you better.

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Kodak created software that restored faded film images. The results were remarkable. As I recall, there were three products in a package called Digital ICE Cube. The original product was called Digital ICE (Digital Image Correction and Enhancement). This software restores film with surface damage plus apples color bias enhancements. The ICE product remains on the market packaged with advanced scanners. The other two have fallen by the wayside. I tell you this because Advanced Science Fiction published numerous papers. These are obtainable and the patents are in the public domain.

This stuff was a spinoff of a little know company in Austin Texas called Advanced Science Fiction. Acquired by Kodak and charged to invent a chemical based color film developing process for mini-labs that was void of effluent chemicals. They succeeded but the developing machine was never marketed.

The film was sprayed with a fine mist of reagent developer and scanned wet. The wetting was so sparse that the film dried in a minute or so. A scan was made to various colors and infrared. Full color digital images resulted. The IR penetrated so surface defects were mitigated. After the scan the film was discarded and the images were burned on a CD or DVD.

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