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The ultimate point I'm trying to solve here is - is there any point in scanning printed photos with a wider gamut than sRGB?

I'm assuming such as standard analogue Kodak negative film printed to appropriate Kodak paper. Is this anything like CMYK or is it something entirely different?
Is the gamut similar to CMYK even if the process is arrived at from a different direction?

Side question: Does this also apply to slides, positives?

My google-fu has failed me on this, as everything I find relates to 'modern' printing from digital to inkjet, giclée, laser etc, so any search I try is buried in modern structures.

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  • \$\begingroup\$ Would you consider CMY to be "like" CMYK? The "K" in CMYK printing is a cost-saver: Black ink is a lot less costly than the amounts of cyan, magenta, and yellow ink that you would need to achieve the same effect. \$\endgroup\$
    – Solomon Slow
    Jan 19, 2021 at 18:23
  • \$\begingroup\$ @SolomonSlow - tbh, I'd consider any info. I honestly have never thought about how classic 'prints' are formed, other than the broadest 'light makes chemicals change'. Bear in mind I do a lot of modern digital to ink & I used to work as an offset-litho machine operator… but this is just one I never considered before now. We're obviously not starting from 'ink' we're starting from 'white paper with chemical treatment'. \$\endgroup\$
    – Tetsujin
    Jan 19, 2021 at 18:26
  • \$\begingroup\$ Do you mean a print on paper printed from a film negative or slide? Is there a problem you are trying to solve or just feeding your brain? "I honestly have never thought about how classic 'prints' are formed," Perhaps the first place to start is research how film that is coated with emulations record light and color onto paper that is coated with emulations accurately. (also, the history of color printing in photography.) - duckduckgo.com/… - tedium.co/2017/04/18/color-printing-lithography-history \$\endgroup\$
    – Alaska Man
    Jan 19, 2021 at 20:01
  • \$\begingroup\$ There's some good starter information on Wikipedia: https://en.wikipedia.org/wiki/Chromogenic_print \$\endgroup\$
    – osullic
    Jan 19, 2021 at 22:14
  • \$\begingroup\$ This has some answers, though not as much detail on the color gamut comparison as I would like: blog.breathingcolor.com/guide-to-digital-printing-part-1 \$\endgroup\$
    – OnBreak.
    Jan 19, 2021 at 22:32

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Getting to your ultimate question about the gamut to use for scanning photos.

The short answer is that yes, it can make sense to scan photos with a wider gamut than sRGB. Modern printers can definitely print colors that fall outside of sRGB (in fact, a fair number even exceed the range of AdobeRGB 98).

The only real question then is what colors you have in the prints you're scanning. That varies drastically.

  • If you're starting from something taken on '80s vintage Kodacolor 400, printed at a typical one-hour photo, and not stored particularly carefully since, then sRGB is probably plenty to capture everything in the picture. Newer films are generally better, but some one-hour printers have gotten even worse, so newer prints aren't necessarily a lot better.

  • If you're scanning something like carefully stored, top quality Cibachrome (aka Ilfochrome) prints, then you'd almost certainly want to use at least AdobeRGB. If it were up to me, I'd do everything I could to be sure nothing was lost--which for color space would mean using ProPhoto RGB, and 16 bits per channel. Then, once it's captured you can try to figure out whether everything you've captured falls within AdobeRGB 98, and if so convert to that (and 8 bits per channel, so the files suddenly get quite a bit smaller). But I'd do my best to capture everything first, then see if it'll all fit in a smaller color space.

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Probably no, because when you are scanning you choose the profile you wish to use according to the scanners abilities. Negatives and slides and prints don't have a profile. I think your question should be: Do I need a wider gamut profile than sRGB when I scan negs, slides and prints. The answer is, No. sRGB should be more than sufficient. Consumer scanners can't reproduce full dynamic range anyway. If you are trying to ensure dark accurate blacks and detailed mids and whites you need a commercial scanner.

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Anything based on the recording/display of light itself is additive color (RGB) based... e.g. silver halide print paper, film negatives, and film positives (slides), LED monitors.

Anything based on pigments is subtractive color (CMYK) based... e.g. inkjet prints.

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  • \$\begingroup\$ I would generalize that reflected color is CMYK and transmitted color is RGB. So I'm surprised you class print paper as RGB. But perhaps I'm wrong. \$\endgroup\$
    – BobT
    Jan 20, 2021 at 2:09
  • \$\begingroup\$ @BobT, yes, CMYK is reflected/subtracted... photographic paper has layers that react to RGB resulting in CMY \$\endgroup\$
    – Steven Kersting
    Jan 20, 2021 at 14:40
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Color print paper is CMY. We are talking cyan (blue-green), magenta (red-blue) and yellow dye only.

Ink based prints such as ink-jet or dye sublimation use pigments and or dye or both. In these systems as well as lithography fail to produce a "good" black. Thus the prints lack sufficient contrast.

A black hue should form when CMY are superimposed. However the cyan and the magenta dye/pigment are not quite the right shade so only a weak black results. To gain the needed contrast a black ink/dye is applied. Old-time printers called this a "kicker" hence the name CMYK.

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  • \$\begingroup\$ It's been decades since ink jets intended to produce photo-quality output have mixed CMY to produce black. Just like "old-time" printers, they use black ink to print black. More recently (like the last decade or more) many have two or three different black inks. And although it's hard to be sure what you mean by "sufficient contrast", by most normal definitions, that claim is just plain wrong. \$\endgroup\$
    – Jerry Coffin
    Jan 20, 2021 at 20:12
  • \$\begingroup\$ The kicker (black) is added because superimposed cyan - magenta - yellow fail to yield a strong black. \$\endgroup\$
    – Alan Marcus
    Jan 20, 2021 at 21:16
  • \$\begingroup\$ Partly--but also because when you're printing black, it's a whole lot less expensive to use black ink than to mix other colors to get black. But the bottom line is that if you're using a reasonably modern, decent-quality ink jet printer, getting good blacks and/or plenty of contrast isn't a problem. \$\endgroup\$
    – Jerry Coffin
    Jan 20, 2021 at 22:59

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