The Late 2015 Retina iMac includes the first wide gamut display that Apple has made for a Mac, able to reproduce colors well outside the sRGB color gamut. I had questions about the P3 color gamut of the new iMac, so I went over to my local Apple Store to check it out.

Up to this point it’s been a conscious choice to buy a wide gamut monitor. I made that choice when I connected a wide gamut NEC PA272w to my Mac Pro. But now the P3 display is built into all of the new 4K and 5K Retina iMacs, so Retina iMac buyers will now be working with a wide gamut display whether they know it or not. While using a wide gamut monitor is generally a good thing, it can involve certain color challenges.

Update: My comments about the P3 color gamut in this article also apply to the 2016 MacBook Pro, which introduced the P3 gamut display to Apple laptops.

Wait…what is the P3 color gamut?

A lot of people have heard of the sRGB color gamut that most computer displays and mobile device displays are based on, and many photographers and designers know that the Adobe RGB gamut covers a significantly larger range of colors. But this P3 color gamut is less well known; what is it and where did it come from?

P3 is based on the color gamut produced by the xenon bulb used in digital cinema projectors. Hollywood uses P3 for mastering because it’s the final output space of motion pictures delivered to digitally equipped movie theaters. P3 is larger than sRGB by a big enough amount that a display that can cover P3 colors is considered a wide gamut display. Many wide gamut displays today are based on Adobe RGB, which I’ll also talk about in this article.

What’s the default display profile of the Retina iMac ?

At the Apple Store I went straight to the first 27″ Retina iMac I saw. The first thing I did was open the Displays panel in System Preferences to check out the list of display color profiles. On many Macs the default display profile is Color LCD. On the iMac I tried, the selected profile was named iMac.

Was the iMac profile the correct profile? I selected “Show profiles for this display only” and the only profile left was iMac. As far as the Mac system is concerned, the iMac profile is the only one that matches up with the display hardware.

What’s the gamut of the iMac display profile?

But what is the size and shape of the iMac profile gamut? Is it closer to sRGB, or P3? For the answer to that, I opened Apple ColorSync Utility. First I clicked on the iMac profile to see the size and shape of the color gamut. Then I clicked the Display P3 profile. They were nearly identical: The iMac default display profile is very close to the P3 color space. This figure shows a top-down view of the 3D plots of those two gamuts side by side…

…and this figure shows the same plots of those gamuts overlaid in Photoshop with the Difference blending mode, which revealed very little difference:

So the default iMac display profile does seem to be P3 gamut, or at least P3 is the target gamut. The difference between the Display P3 and iMac profiles is probably that the iMac profile represents the color gamut that the display panel is actually capable of reproducing.

However, neither the iMac display profile nor Display P3 is exactly the same as the DCI-P3 digital cinema standard. A backlit device display reproduces images differently than a cinema projector in a dark theater, so when Apple adapted DCI-P3 into their own profile that they call Display P3, Apple adjusted their version to be more consistent with typical computer displays. According to the Apple Developer API Reference, Display P3 “uses the DCI P3 primaries, a D65 white point, and the same gamma curve as the sRGB color space.” It looks like Apple wanted to keep as many sRGB characteristics as possible as they expanded the color range to the P3 color gamut.

What if we compare the iMac profile to the Color LCD profile that is also found in the list of display profiles on this iMac? The Color LCD profile gamut is much smaller than the iMac and P3 profiles. However, the Color LCD profile is close to the sRGB profile, so I’m not sure why the Color LCD profile is even included with the iMac because its gamut is too small to describe the iMac display.

At the Apple Store I didn’t have time to do much testing with real images, but an excellent article at astramael.com (The Wide Gamut World of Color — iMac Edition) does use sample photos to show the tradeoffs between the Adobe RGB, P3, and sRGB color gamuts. That author also tried something that I didn’t: They brought a colorimeter to the Apple Store, hoping to make their own profile and gamut plot of the P3 display. They report that the Apple Store staff did not allow them to connect and run the colorimeter. For that reason, both that author and I are comparing the Apple-supplied profiles that we found on the iMacs themselves. The Apple Store I went to had no problem with me copying screen shots and profiles to my USB flash drive.

Note that for true digital cinema work, just having a P3 color space isn’t enough. The Digital Cinema Initiative (DCI) standard also specifies a gamma of 2.6 and a luminance of 48 cd/m2 or 100 cd/m2 depending on whether you’re targeting movie theaters or television, and there are also various white point standards. The iMac at the Apple Store was set to maximum brightness which is way too bright for digital cinema or print work, so you’ll need to crank down the brightness of the iMac display and probably still have to use a display profiling device to make sure the display is hitting the correct gamma, luminance, and white point numbers for the specific standard you’re targeting.

How does the iMac P3 display handle untagged objects?

One of the challenges of wide gamut displays is that the colors in untagged objects (objects without a color profile) can appear oversaturated. This can happen when the color values of untagged objects are defined in a smaller color space such as sRGB, which is usually the case. When those untagged color values are displayed on a larger gamut display, if their gamut is simply scaled up to match the larger gamut the color values can end up further out than they should be in the larger color space, appearing oversaturated.

I believe I saw evidence of this when looking at the Late 2015 Retina iMac. I looked at things like the colorful icons in the Applications folder and the graphics in the Maps application. I opened the same windows on the iMac and on a 15” 2015 Retina MacBook Pro near it. Even when I turned up the brightness of the MacBook Pro all the way, the colors in the iMac screen were much more vivid. Not just “this display shows more colors” saturated, but some colors seemed to have that unnatural “radioactive” glow that’s associated with untagged objects on wide gamut displays. To me this indicates that Apple may not have completely color-managed Mac system elements for wide gamut displays. I see the same effect on untagged objects when my NEC PA272w display is in wide gamut mode.

I hope to hear more about general untagged color handling on this display from anyone who knows more or is able to test it more thoroughly.

As for the Web, it looks to me like untagged image and CSS colors are rendered correctly in the Safari web browser, but not necessarily outside Safari, such as in the Finder. The tweets below explain why untagged colors in Safari are no longer as screwed up as they used to be on a wide gamut monitor: Safari now does the right thing, in that when Safari 9 sees colors without a profile (untagged) it will assume the colors are in the sRGB color space and convert to wide gamut from there. When Safari sees an image that is tagged with a color profile it will continue to do what it correctly did before: use the image’s profile to convert its colors to the wide gamut display profile, in this case iMac P3.

New iMacs have wide-gamut displays. Safari will correctly treat CSS colors as sRGB, and render wide-gamut images.

— smfr (@smfr) October 13, 2015

For web developers on the 2015 iMac: only Safari 9 correctly treats CSS colors as sRGB. Chrome will oversaturate. https://t.co/hrLETHbysl

— Ricci Adams (@iccir) October 19, 2015

Does the iMac P3 display have an sRGB mode?

Wide gamut displays can be a challenge for developers of games, mobile apps, web sites, and other content targeted for average consumer displays, because of the oversaturation of untagged content that I just described. Colors can appear unnaturally intense if they’re not mapped properly to a wide gamut display.

Professional wide gamut monitors work around the oversaturation problem by providing an option that restricts their gamut to sRGB. Some let you switch to an sRGB emulation mode through a control on the front panel of the display; with others you switch modes using utility software. The Retina iMac doesn’t do it either way, or at least not in any way that I was able to find. When I searched the system help files of the iMac for “P3” or “sRGB” nothing came up. In general, the Mac help files for color management are pretty thin.

If the iMac P3 display doesn’t have a way to emulate an sRGB display, buyers of the Retina iMac should be aware that colors might not display as expected in untagged objects or in applications that are not color managed. I’m not 100% sure that there is no sRGB emulation mode on this display, but that’s how it’s looking. If you have more information on this, please post in the comments.

You may sometimes see a suggestion to open the Displays system preference and select the sRGB profile. That is not going to help, because that’s not how display profiles work. A display profile describes the color behavior of the display, but it can’t change that behavior. So choosing the sRGB profile can’t and won’t make the monitor display the sRGB gamut. What choosing an sRGB profile will do is lie to the OS about the color gamut of the monitor, saying that the display is sRGB when it isn’t. That lie will cause colors to display incorrectly.

But it isn’t Adobe RGB! Or does that matter?

Some creative professionals who don’t work in video may be concerned that Apple has gone with a P3 panel instead of an Adobe RGB (1998) panel. After all, Adobe RGB has been the de facto standard for a wide gamut color space. When there’s a color space option other than sRGB in a photography or graphic design application or on a digital still camera, Adobe RGB is usually the alternative you get. For that reason, Adobe RGB is the gamut around which most wide gamut displays are built, such as those made by Eizo, NEC, and Dell.

By specifying a P3 gamut panel for the Retina iMac, Apple has consciously gone in a different direction. But you shouldn’t automatically conclude that P3 is going to ruin Adobe RGB workflows, because P3 and Adobe RGB are mostly the same size and shape. With P3 you do lose a few blues and greens, but you gain some yellows and reds. If color management is set up properly on your system, it will compensate for whatever color space your display uses and you should see consistent color. The only way P3 might be harder to use compared to Adobe RGB is if your work often involves the relatively few colors within Adobe RGB that are not within P3.

I did see one possible area of concern when comparing some CMYK/print color gamuts against Adobe RGB and P3. Some of the print blues and greens that Adobe RGB can cover look like they aren’t covered by P3. If print is an important output for you, you might want to compare the gamut of your typical printing conditions against P3 to find out if you would rather have an Adobe RGB display. But you’ll still see more CMYK colors with a P3 display than you would have with an sRGB display.

Note that the gamut plots I’ve shown are generalizations. For one thing, the size and shape of each gamut varies with luminance, so for example the P3 gamut is going to look a lot different when you dim it down to the DCI luminance spec for a digital projector. If you’re after the best possible visualization of gamuts, rotate them in 3D to see how they behave from light to dark. ColorSync Utility can rotate its 3D gamut plots, or you can use a more advanced gamut analysis tool such as Chromix ColorThink Pro which can also include sample images as part of the analysis.

The P3 iMac: color management required

I welcome any corrections to this article from color professionals who may have more hard data about how the P3 display works on the Late 2015 Retina iMac, and whether the Mac system was adjusted in any way to better handle wide gamut displays. Especially because my time with the new iMac was limited. But until I hear otherwise, here’s my take on it.

The wide gamut display of the Late 2015 Retina iMac should give you the best color you’ve seen on an Apple display, as long as you work in color-managed applications with content tagged with embedded color profiles. But untagged objects and colors in non-color-managed applications may display with distorted colors when rendered on a wide gamut display like this one. Because the Late 2015 Retina iMac display doesn’t seem to have an sRGB mode, if you need to proof colors for sRGB output, such as graphics in a game or app, or on a web page in a browser other than Safari, you may want to connect an inexpensive sRGB-calibrated display to the iMac.

If you’re creating work that targets larger color gamuts than sRGB, such as fine art printing or digital cinema mastering, the wide gamut P3 display of the Late 2015 Retina iMac looks like a real improvement over previous iMacs, especially if you’re working in a color-managed environment.

If you’re currently using a conventional sRGB-based display, the important difference is that P3 is still a big step up from sRGB, about the same as going from sRGB to Adobe RGB. You win about as much as you would have if the iMac had an Adobe RGB panel.

I’ve read about photographers who bought a wide gamut display and plugged it into the iMac because the built-in displays on the older iMacs didn’t completely meet their needs. Now that the current Retina iMac includes a wide gamut display, most iMac-using photographers no longer need to buy and plug in a separate wide gamut monitor and give up the desk space for it. For those photographers, the new P3 display of the Late 2015 Retina iMac should save them several hundred dollars and free up a few square feet of desk space.

(There is one more thing: While examining the color profiles on the iMac, I noticed several profiles I’d never seen in the Mac system before. Those new profiles have one thing in common, and I talk about that in the next article: New OS X Color Profiles Strengthen Mac Digital Cinema Support.)