4 Replies Latest reply: Oct 25, 2009 5:07 PM by George Austin RSS

    JPEG to ACR Color Shift

    George Austin Community Member

      Why aren't RGB color values strictly preserved when opening a jpeg in ACR?

       

      For example, using ACR ver 5.3 with all sliders zeroed, an RGB 143/127/0 jpeg patch becomes 149/127/30 in ACR.

        • 1. Re: JPEG to ACR Color Shift
          D Fosse-QDEaQ1 Community Member

          Is it just the numbers, or is it visibly changing as well? I did some testing here and I don't see any shift as long as I stay in the same color space. Changing space will shift the numbers, but there shouldn't be any visible change unless it's clipping.

           

          Anyway, I see similar questions from time to time and it seems to have everyone stumped. Here's one from the PS Mac forum, this too with zero replies (but you might want to keep an eye on it): http://forums.adobe.com/thread/511723?tstart=0

           

          I'd like to see an explanation for this, so I think you should post it in the ACR forum. Maybe Jeff or Eric can come up with something.

           

          BTW; you should be on 5.5.

          • 2. Re: JPEG to ACR Color Shift
            George Austin Community Member

            "...Is it just the numbers, or is it visibly changing as well?..."

             

            It may well be just the numbers, because side-by-side on the same monitor I cannot discern any difference, and when I open the ACR version into photoshop, the original jpeg color values (143/127/0) are restored. Then again, when I put two jpeg patches side-by-side, one RGB 143/127/0 and one RGB 143/127/30 I really can't see a difference. Since I'm not known for visual acuity, I can't be conclusive about their relative tones. Thanks for responding.

            • 3. Re: JPEG to ACR Color Shift
              D Fosse-QDEaQ1 Community Member

              Well, there was an answer in that other thread I mentioned, but I don't buy it. Something very fishy with the color settings there.

              • 4. Re: JPEG to ACR Color Shift
                George Austin Community Member

                Apparently this is no more than a color space switch. The PS color space in use when I created the original jpeg patch was sRGB. Opening that jpeg in ACR resulted in the shift noted. But using the same RGB entries, with Adobe 1998 as the color space, resulted in no shift when opened in ACR.