Photoshop allows enabling or disabling GPU support (Preferences => Performance => Graphics Processor Settings). For years now, I’ve disabled the GPU due to too many glitches and bugs. But under OS X Yosemite, the latest version of Photoshop CC 2014 becomes extremely sluggish with a brush or spotting tool with the GPU off. So one wants to enable the GPU for such uses.
But enabling the GPU comes with a serious drawback to my daily work: Fit to Screen on a 2560 X 1600 display results in a blurry image. This makes it very hard to assess multiple images.
Disabling GPU support delivers far superior fit-to-window sharpness. I’ve tried different cache levels and GPU settings, all to no avail. GPU support is just plain broken for zooming in Photoshop; some zoom levels are sharp and others are awful. Actual pixels is of course just fine, but then one cannot see the image as a whole. Surely a fast GPU can render a reduced size image far better than is being done (dual GPUs in Mac Pro!).
The blur or sharpness depends on the amount of zoom relative to screen and image size, so a different size image or display might be fine for some users. And indeed some zoom levels are reasonably sharp, but never fit-to-screen.
In my case, a 36MP image on a 2560 X 1600 display is awful at fit-to-window. I reported this to Adobe over two years ago, but nothing has been done. It sure is frustrating. I have emailed two Adobe contacts about it today, and I hope to hear something affirmative on addressing it.
UPDATE: I’ve heard back from Jeff Tranberry at Adobe, and they are looking into it.
The image below is a crop of the whole. Observe the blur with GPU enabled and sharp image with the GPU disabled (toggle).
Click for a full size image.
The issues with the GPU do not stop there. Enabling the GPU still results in various drawing bugs such as this mangled mess. Moreover, Photoshop benefits minimally if at all for common operations either with one GPU or two.