This site has supported Retina-grade images for some time now.
I installed the latest Photoshop CS6 13.0.2 update which promises HiDPI (Retina) display support. The text and buttons and user interface elements have that wonderfully sharp etched look that comes from using the full screen resolution.
But it is the drawing of images at full display resolution (instead of being pixel doubled) that really stands out as the big win—
Shown below is a screen shot of a 2880 X 1800 image displayed on a MacBook Pro Retina; a white border has been added show its outline. It fits the screen perfectly in its full HiDPI glory.
Working in Best for Retina display resolution is ideal for Photoshop HiDPI support, but it means that other programs used at the same time effectively see a 1440 X 900 display. This makes the working space cramped in those programs. The solution is to use one of the scaled modes (such as the 1920 X 1200 “More Space” option), but in scaled modes there is no true actual pixels in Photoshop (1 image pixel = 1 display pixel).
Scaled modes are somewhat suprising
The screen on a MacBook Pro with Retina display is 2880 X 1800. Therefore, an actual pixels rendition might reasonably be expected to draw a 2880 image so that it exactly fits the 2880-pixel-wide screen resolution— no scaling that can alter or blur detail, just lay down those pixels unaltered.
But it’s more complicated than that when display-scaling other than 2:1 is used. This is not a bug, but a natural side effect of having a virtual display (for scaled modes) that has to be drawn to the actual 2880 X 1800 screen size.
As shown below, the 1920 mode (“More Space”) is one of the “scaled modes”— applications behave as if the actual screen were 1920 X 1200. But it’s actually some fancy footwork in OS X having 3840 X 2400 pixels to work with (pixel doubling) which are drawn (scaled) onto a 2880 X 1800 display. Ditto for any of the other modes; 1680 X 1050 gets turned into a 3360 X 2100 pixels drawn to the display. Making a screen capture actually yields the pixel-doubled image size (e.g., 3840 X 2400 for 1920 X 1200 mode).
Below is the same image as further above, also atin Photoshop CS6 (actual pixels) but with the display set to 1680 X 1050 scaled mode. Even though it’s scaled as displayed, the image still looks really good with all those pixels being used, and this might be important for detail work or image assessment, so beware of the difference.
As far as Photoshop is concerned, the image is at actual pixels; there are 2880 pixels of image width drawn into a 3840-wide virtual display. As far as the screen display, it is not actual pixels (one image pixel is not one screen pixel).