Color Profile Question with Round Trip Editing with Photoshop

[digitaldog]

The sRGB profile does have a true TRC and not a gamma curve and Photoshop honors this. In Color Settings, when you futz around with the gamma settings, you'll probably not get this TRC. IOW, typing 2.2 gamma should provide this while the actual sRGB profile has that funny bump down in the shadows.

If there's some old software that accesses the sRGB profile as designed, and uses a simple 2.2 gamma curve, well you probably don't want to be using that product assuming it can even run on a modern OS.

[deejjjaaaa]

Well, there are situations under which it could. E.g., many older apps use an approximation to the sRGB tone curve rather than the correct curve with the "kink" in the shadows. If you round tripped multiple times between LR and one of those in a space with a sRGB tone curve, then you could get a change in the shadows. But in this case the OP is asking about Adobe <-> Adobe round tripping, and so far as I am aware Adobe use the same math in all their products.

Sandy

yes, but is that math precise enough to handle roundtrips where different colorspaces coordinates and different curves are used, as we are talking about recalculations between prophoto coordinates w/ g1 inside and different colorspace/curve outside

PS: and I am not sure that math is the same either... it is ACR/LR vs PS... different code, isn't it ?

[samueljohnchia]

Andrew, you are right. I do apologise if my post confused anyone. I am intrigued though, since Photoshop calculates alpha channels of the current document based on your gray gamma settings in Photoshop, which means that one cannot use any special tone curve that is not a gamma curve, or the  curves Photoshop uses for dot gain. I wonder how the dot gain curves are calculated.

[sandymc]

yes, but is that math precise enough to handle roundtrips where different colorspaces coordinates and different curves are used, as we are talking about recalculations between prophoto coordinates w/ g1 inside and different colorspace/curve outside

PS: and I am not sure that math is the same either... it is ACR/LR vs PS... different code, isn't it ?

Yes, I did say "except to the extent that implementation specifics such as rounding/15 bit precision in the engine impacts on you"    But I'd be surprised if there was a visible difference without doing a LOT of round tripping.

Personally, I've never seen any difference between how LR and PS handle tagged images. I'd think, but have no evidence other than that ACR and LR share common code for raw processing, that the color management code was very similar.

Sandy