3 Replies Latest reply on Nov 11, 2014 2:46 AM by StructAural

    30 Bit Display Layer Combination Accuracy Question

    Noel Carboni Level 8

      I have an ATI 5670 and I find I can enable the [ ] 30 Bit Display checkbox.


      I know my monitors can't show 30 bit data because they're hooked up via DVI and VGA, but what I was hoping I might find is that the image pyramids inside Photoshop, where multiple layers are combined to form downsized images for quick preview, would be calculated using higher precision when this setting is enabled. Unfortunately, I don't find this to be the case.  The layers still seem to be combined with 8 bit accuracy.


      Here, for example, is a 16 bits/channel astroimage with an extreme curves adjustment layer over a relatively dark image. It's at 33.33% zoom in this screen grab.  Note the posterization.




      This is what it looks like if I choose Layer - Flatten:



      The reason I want higher quality combinational logic should be obvious from the first image above.


      I also find the posterization goes away if I view the image at 100%, but that makes it impossible to see the entire image so doing things like image-wide field flattening isn't effective.


      Now, I DO have a reasonably effective workaround, though it's not perfect:  If I set the Cache Levels to 1 in the Performance dialog, and switch graphics processor usage to Basic, I find I can work at any zoom level and the image layers are combined at full 16 bits/channel accuracy.  In fact, this workaround is more viable for Photoshop CS6 than it was for Photoshop CS5, since with the older version I found I had to disable OpenGL Drawing entirely to avert crashes.  Now it hangs together on Basic mode, so that's nice.


      But unfortunately with Cache Levels set to 1 some things get mighty slow, and I really wouldn't want to leave it set this way for general photography editing.  At the moment I leave 32 bit Photoshop set at Cache Levles 1, while 64 bit Photoshop is set with Cache Levels at the default (4 or 6 I think), and I use one or the other depending on the kind of work I'm going to do.


      It seems to me that the [  ] 30 Bit Display setting should effect a change to a higher accuracy mode for layer combination, otherwise people with actual 30 bit displays who use layers may sense posterization as well. 


      Adobe (Chris?):  Any plans to update this?  As I recall back last time I brought this up we heard that it's not a trivial task.  Alas, I had been hoping it might be done for Photoshop CS6.