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I've always read that normal users should stick with AdobeRGB and not use ProPhoto for the working color space. But why? Does it affect the ability to edit and make sense of color changes?

I ask because Lightroom sends work to Photoshop using ProPhoto (by default) and there are also considerations to not use different color space for image and working. In fact, PictoColor does not work unless the image profile matches the working space.

So, why not set Photoshop to use ProPhoto for its "working space"?

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  • Would the late downvoter please comment? If it's not a perfectly good question, please explain why and how it can be improved.
    – JDługosz
    Oct 2, 2015 at 5:20

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One reason not to use an extremely wide colour space like ProPhoto is that it stretches the colour values unacceptably wide when editing in 8 bit mode. You only have 256 levels for each colour to work with, and with a wide colour space, that means that the difference between two adjacent values is perceptible, leading to posterization.

Of course, in 16 bit mode, as Lightroom exports to PS, this is irrelevant, so if you work in 16 bit or higher, you can use a wide colour space.

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  • > it stretches the colour values unacceptably wide when editing in 8 bit mode -- true, this reason is also often cited.
    – Iliah Borg
    May 25, 2015 at 18:43
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The most commonly given reason against the use of ProPhoto RGB as a working space is that monitor gamut is much narrower, so there is no WYSIWYG when editing. Another reason is that ProPhoto RGB contains imaginary colours, not present in Lab space.

However, colour conversions add some noise and may also add artifacts. Lightroom and ACR are using ProPhoto RGB primaries internally, so quite a lot of folks have their default working space in Photoshop also to ProPhoto RGB; soft-proof to destination colour space when editing, and convert to destination colour space before save - this helps to eliminate both arguments against using ProPhoto RGB in Photoshop.

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  • Use ProPhoto color space if you have a reason and want to take the time to learn how. I would not recommend it as a default for most users because of the training time.
    – Aaron
    May 25, 2015 at 17:24
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    @ A K Photo : but if one is using Lightroom and/or ACR, he is already using ProPhoto, so maybe learning it is time well-spent ;)
    – Iliah Borg
    May 25, 2015 at 17:26
  • What needs to be learned about it? Can you point to an article or something?
    – JDługosz
    May 25, 2015 at 21:44
  • The imaginary colors are a subset of Lab, not disjlint from it. upload.wikimedia.org/wikipedia/commons/thumb/1/1e/…
    – JDługosz
    May 25, 2015 at 21:47
  • @JDługosz : Not specifically about ProPhoto, just how to deal with wide gamut spaces on limited gamut monitors. That is, "by numbers" approach (Dan Margulis books, specifically "Photoshop LAB Color: The Canyon Conundrum...", his Professional Photoshop, and Modern Workflow). Bruce Lindbloom has some fun facts on ProPhoto on his site, also on the topic of imaginary colours en.wikipedia.org/wiki/Impossible_color ; and Andrew Rodney on softproofing.
    – Iliah Borg
    May 25, 2015 at 22:37

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