The Retina Display iMac for Photographers, Part ll

Visual color assessment of the Retina iMac’s display shows it to be close to the target values, closer than many off-the-shelf displays. Its color and densities, out of the box, would be better for general consumer use than almost any other solution, short of top-end dedicated graphics displays.

That’s great news for most users, but not quite enough for those doing serious color work, including photography, on the iMac. The display we tested was just a bit denser in the midtones than would be ideal, and the colors are a bit punchy.

More obvious than either of those issues was the lack of neutrality; in fact, on an uncalibrated display the grays were sufficiently off-neutral to make it difficult to judge the other.

Analyzing the iMac display with a Datacolor Spyder profile provided some understanding of these visual issues. So let’s dig into the details this tool can provide us about the display.

First is the Gamma Curves. Lets start with a chart of the red channel, showing the target of gamma 2.2 in red, and the native curve in black.

RedUncal

See how it’s a bit below the 2.2 line? That would begin to account for part of the midtones being too dark. Next, lets look at the calibrated results. The black line lying right over the red target line is the corrected result.

RedCalandUncal

The green channel shows a similar story here is the green channel, with the uncalibrated line below the target, and the calibrated line nearly on top of it.GreenCalandUncal

The blue channel looks rather different. Here the uncalibrated curve lies above the target through much of the curve, but below it in the highlights. Corrected blue curve left out for clarity.

BlueUncal

It’s the combination of small variations in channel curves that add up to a slight inaccuracy in the overall density, as well as the gray balance.

Next let’s look at the gamut of the display. Apple has been standardizing on an sRGB gamut, for the simplicity of having sRGB web images, as well as Rec 709 video, look more or less correct on screen.

In the image below you can see that the red triangle representing the display gamut is a good match for the green triangle representing sRGB. In Apple’s laptops and mobile devices, the gamut is very close to sRGB, but a hair inside, generally rating 97 to 99% of sRGB. However, the display gamut is outside of sRGB, especially at the red and green points.

iMacGamut

This would account for colors on the display being just a bit punchy, a direction that would please general users, but would bother advanced photographers, especially in the skintones. Correcting this oversaturation in an editing app on the iMac would then result in desaturated colors in color-accurate prints. This is where a user-generated correction profile for the display is key to success!

Other functions of the display rated well, with the exception of the uniformity issue that is the weak point of most white LED lit displays. Color accuracy on all colors except for the Cyan patch (which is outside the sRGB gamut) were in the range of 1 delta-E, or barely discernible. Contrast measured at over 1000 to 1. Other factors can be seen in the summary chart below.

iMacSummary

As can be seen from this table, as long as you don’t depend on the brightness in the corners of the screen, the Retina iMac display is a very good display.

The brightness of the iMac display would be the last issue to consider. This screen is capable of producing 500 candelas per meter squared. That would be great for use on a tradeshow floor, but in a normal, dim editing environment it is critical to dim this display to an appropriate level.

We calibrated it to 120 candelas, as we do with our other displays, and it worked very well at that level. If you have other custom settings you require, such as calibrating to 5800K instead of 6500K, etc, then custom calibration is a necessity.

Pairing the Retina iMac with a wide gamut graphics screen as a second display offers the best of both worlds, including the ability to view nearly the entire image from most DSLR cameras on one screen at 100% scale, making dust busting and sharpening a joy. Calibrating both those displays to make the match between them as close as possible can provide a great image editing experience, saving time and providing a good screen to print match.

Thanks to Datacolor for the tools used to analyze the Retina iMac display!

C. David Tobie

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