30-bit display color is now supported by OS X and Photoshop

For many years, Photoshop users and other graphics professionals have wanted proper support for 10-bits-per-channel video displays (also known as 30-bit when counting the three RGB channels together) on Macs. This isn’t about the file format, but the data path to the video monitor. The 8 bits per channel displays almost all of us use today may show banding when displaying gradients, especially in grayscale images, shadows, and in colors dominated by a single channel. That banding goes away on 10bpc displays because of the additional display levels available to each channel.

While 10bpc-capable displays, graphics cards, cables, and software (such as Photoshop) have been ready for some time, OS X itself has been the last missing piece everybody has been waiting for. Some developers earlier found clues in El Capitan that seemed to indicate 10-bpc display support, and now some users are finding that OS X is reporting 10 bits per channel from some Retina iMacs and Mac Pros, as in the following tweet is from Juergen Specht.

It’s difficult to find detailed information about 30-bit color in OS X, such as the requirements to make it work. Apple doesn’t seem to have published anything about it.

Also, without mentioning it in their release notes, Adobe added a new “30 Bit Display” option in the Photoshop CC 2015.1 that came out on November 30, 2015. Photoshop users found the new option themselves and started talking about it online. You’ll find it in the Preferences dialog box; click the Performance tab and then click the Advanced Settings button, as seen in the next figure. This screen shot is from a 2011 15″ MacBook Pro with discrete GPU and the built-in display only; this surprised me because up until now I heard you had to have a very recent Mac to use 30-bit color. But there it is (click image to enlarge). I just turned it on, so I still need to see if it makes any difference in gradients on the MacBook Pro screen or my NEC PA272. I don’t expect it to make much difference on the old MacBook Pro screen.

Two sets of full screen controls in Lightroom

Lloyd Chambers at Mac Performance Guide claims to have spoken with a contact at Adobe who said “Apple supports 30-bit output on iMac 5K under 10.11, while other devices get dithering with that option checked.” That raises the question of what OS X 30-bit color really does, especially with different combinations of graphics cards and displays. I wouldn’t expect my old MacBook Pro screen to do any better than dithered 30-bit.

Windows has technically supported 30-bit display color for some time, so I believe it was already possible to see the 30 Bit Display option in Windows. But I’ve been told that there are a number of technical constraints to get 30-bit color in Windows and so it isn’t necessarily enabled on a given Windows system or application (and usually, it probably isn’t enabled). Again, it’s hard to tell when it works and what it actually does.

I am not yet sure if Lightroom or Adobe Camera Raw support 30-bit color, though it is potentially just as useful in that software as it is in Photoshop.

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