New article on color management

Started Apr 26, 2013 | Discussions thread
crames Regular Member • Posts: 192
Re: Camera-->sRGB versus Camera-->ProPhoto-->sRGB

gollywop wrote:

crames wrote:

gollywop wrote:

crames wrote:

sRGB might not be the best color space in which to do white-balancing. Another reference here. (sRGB has the same primaries as ITU-R BT.709 compared in these references.)

I'm not sure what you're talking about here, Cliff.  If you're shooting raw and doing white-balancing in ACR, the result is the same regardless of which working space you've chosen.  If you're talking about white-balancing a jpeg in PS -- well, there you're on your own.

Well, it depends on one's workflow, doesn't it? Just more reason to avoid editing in sRGB.

"Reason"? . . . no.

Jack said, "Compare this to moving to the output space at the very start and then applying rendering/adjustments.  Chances for error would intuitively appear to be minimized in this case, no?"

If you want to do white balance and other adjustments in ACR, then you'll not be "moving to the output space at the very start," and in fact none of the operations performed in ACR will have been accomplished in the sRGB space, since ACR uses a linearized ProPhoto internal space.

If you were to white balance in ACR and do the rest in sRGB, of course you will not run into the potentially sub-optimal white balance problems described in the papers I referenced. On that basis, yes, white-balance issues would not be a "reason" to avoid sRGB. Despite having avoided the white-balance issues, you will still be faced with the possible hue shiifts during other routine editing operations after moving to the sRGB space. It's not hard to imagine that sometimes it is necessary use PS to selectively touch up the white balance of a digital photo taken in mixed lighting, or even skip ACR completely, for example when editing a film scan. In such cases the potential white balance issue is another "reason" to avoid sRGB .

In answer to Jack's original question, I think that one has more control over the conversion to sRGB if the conversion and gamut-mapping to the smaller sRGB space is saved for the end, because then you have the full controls of PS to deal with any out-of-gamut colors. By going camera space -> ProPhoto -> edit -> sRGB, you have the opportunity to identify out-of-gamut colors and smoothly bring them into gamut by selective desaturation. If instead one converts to sRGB at the very start, you really have no control over the mapping of the out-of-gamut colors - in most cases they will be simply chopped down to the gamut boundary.


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