Getting the most accurate color in scans of old documents, photographs, etc.

Started Aug 10, 2022 | Questions thread
OP GTaillefer New Member • Posts: 13
Re: Getting the most accurate color in scans of old documents, photographs, etc.

Overrank wrote:

GTaillefer wrote:

Overrank wrote:

GTaillefer wrote:

Overrank wrote:

GTaillefer wrote:

Again, the point isn't for making it presentable to people, the point is to get as an exact possible digitization of the original object. I'd prefer spending my time on trying to get as many exact digitizations of the objects in question as possible than spending time editing them.

What you want to do isn’t particularly unusual. There are guidelines e.g. FADGI, that will help you to do this and you can search and purchase FADGI compliant scanners e.g. https://www.shi.com/Product/44445856/Kodak-i5850-FADGI-compliant-Scanner-Bundle

At a sub-$1,000 level (rather than >$100,000) then for photographs (rather than negatives or slides) you need a flatbed scanner, a reflective colour target and software than can apply the calibration from scanning the target to each scan that you do. I do this all the time when I scan transparencies using an IT-8 target suitable for the slide I am scanning,

Thank you for the response, I'll have to really look into the FADGI guidelines (someone also gave me a link to Canada's gov guidelines on the same thing so I'll have to check those out as well) to see everything for myself. As I've said earlier in this thread, I'm wary of actually modifying the images, so would buying a calibration card, putting it in the scans, but not editing it and let others edit copies if they want to work? Or should I just leave it to using color correction cards (you know the ones used for photography that I mentioned that I've seen used people scanning with)

When I scan transparencies using a scanner that’s been calibrated then the image I get already has the changes made as the purpose of the calibration is to correct for the error in the scanner. This means that if I scan a slide on a callibrated Plustek or Reflecta or an Epson V550 I get pretty much the same image colouring,, whereas without the calibration they would be different. Don’t think of the calibration as modifying the image, it’s just correcting for errors in the scanner (the changes it makes are pretty subtle).

So if these errors exist, then why didn't the manufacturers fix them in the first place? Or is it a thing to correct for specific items that you are scanning across scanners? Or are these errors specific to individual scanners (regardless of model). And in any case, what are those problems/errors? Are they errors against capturing the light that is exactly being reflected off the scanner LED lights or is it how we as humans perceive the light being reflected off the object normally (not scanner LED)? Again I would like to thank you for your helpful responses to my question.

Think of it in the same way as people calibrate monitors using something like a Spider. You are correcting for the per sample differences in the monitor colours, and also that monitor colours change with age. In the same way with a colour calibration chart on a scanner you are correcting for differences in individual scanners, both new and as they age.

As far as I understand the mechanics of it the corrections are against what the colours should be. When the targets are made a sample target has the patches measured very accurately. It’s known what the colours should be, and what they’ve been accurately measured as (you get this measurement file with the target), then by measuring what the scanner reads for each colour it is it’s possible to calculate a correction to move everything back to the correct values.

Alright thank you so much for your help! Are there any good calibration cards that you would recommend (hopefully that are cheap)? I am currently using Silverfast as my application for scanning but I'm sure they work universally. Thanks

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