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

Advertisements

The Retina Display iMac for Photographers, Part l

In a few short years the iMac has moved from being a rather slow, utilitarian looking machine that could not be recommended for photo or video work, to a big, beautiful device with wide viewing angles, high resolution displays, and full external display support. Apple’s new 27-inch iMac with Retina Display takes this evolution a big step further.

Until recently the question has been: is the iMac an acceptable image-editing machine for basic users, who can’t justify more expensive equipment? And once IPS (In-Plane Switching) screens with wider viewing angles, wider ranging dimmer controls, and better external display support were added, the answer was finally “Yes”.

With last year’s much anticipated announcement of the new smaller form factor MacPro, high-end 3D animation and video work quickly moved to that machine. But photographers, even those who do some time lapse or video work, were more reluctant to purchase the new MacPro. It had some impressive specs, but it was pricey as well, and the addition of one or more 4K displays, which are a main reason for owning such a computer, added thousands more to the cost of configuring one. The addition of Thunderbolt 2 storage arrays for holding the images and video in question resulted in a total price that was only justifiable for full time video or timelapse professionals, who could earn back the investment in a relatively short time.

Fast forward to the recent release of the new Retina iMac, and the balance becomes clearer. The Retina iMac sports the world’s highest resolution screen, called 5K, but displaying 67% more pixels than a 4K screen. This means it is capable of showing more of your image pixels at one time than any other display, and pixel count is a major factor for photographers, in sharpening, dust busting, and when available, for every other step in the selection and editing process. The Retina iMac also offers the world’s fastest quad-core PC processor, meaning that for anything other than massive parallel processing it actually works faster than the MacPro, which uses a generation older processor. Latest generation graphics processors were also needed, along with a custom scaler to keep up with this huge screen resolution.

The clear answer is that the Retina iMac is unquestionably the best still image edting system available, and a steal at the price. After all, it’s possible to spend more for a single 4K display then the entire cost of a Retina iMac. Those who are running three or more 4K displays, and rendering large amounts of video while doing other work on their computers will still want the MacPro; though one could make a case for them also needing a Retina iMac as a second machine.

For the rest of us the Retina iMac is the right answer for photo, time lapse, and for HD or moderate amounts of 4K Video. But if this is clearly the best option for photographers, what configuration is best? Here the answer depends on your budget and your needs.

Configuration Options, in approximate order:

• Base configuration: fine for casual photo work
• First upgrade: add more memory (RAM)
• Second upgrade: processer speed upgrade
• Third upgrade: larger Fusion (composite Flash and Disk) Drive
• Forth upgrade: external drive array, and Flash instead of Fusion internal drive
• Fifth upgrade: Thunderbolt 2 external arrays, mostly for heavy video work
• Other Upgrade Option: A second display. No clear location in the list above.

There are a few other specifications for the Retina iMac display that photographers need to consider before making the investment in one of these machines.

First is uniformity. Low cost screens tend to be much brighter in the center than at the corners, and white LED edge-light displays, of the type Apple users, are prone to quite a bit of uniformity variation. The Retina iMac screen keeps brightness variations to about 10% total, which is about as accurate as large, white edge-lit displays can be. For more uniformity than that, it’s necessary to move to a more expensive backlight type.

Screen reflectivity is the next factor. Displays used to have a matte surface finish to blur reflections, making them less distracting. Many graphics displays still use this strategy, though the coatings have become much finer grained, to allow the higher resolutions of modern screens to show through. Matting the surface has the disadvantages of reducing the viewable dynamic range, making the screen less vibrant. Apple was a pioneer in the use of glossy glass screens on modern LCD displays. Graphics users objected, but as improvements reduced reflection on the gloss screens, though bonding screen elements together to reduce air layers and secondary reflections, and by applying special anti-reflection coatings to the surface of the screen, gloss screens now offer serious advantages over matte finishes.

Color Gamut is the final concern. Just because a feature is marketed doesn’t make it important. Don’t assume that the wide-gamut of high-end displays is their most important feature.

The comparison is interesting. Those who have worked with good quality sRGB and AdobeRGB displays may find that the difference in gamut is less of an issue than other factors, most typically resolution. When using a larger or higher resolution sRGB display, and a smaller or lower resolution AdobeRGB display, many find themselves editing exclusively on the screen with more pixels, and, perhaps, moving images to the wide gamut screen for occasional color checks in the saturated Yellows, Greens, and Cyans. So the Retina iMac’s sRGB-sized gamut might not be a show-stopper for many photographers.

Stay Tuned for Part Two of this series, which will cover, with illustrations, the color accuracy of the Retina iMac display; specifically its gray balance, gamma smoothness and accuracy, whitepoint accuracy, and color gamut. As you will see, it does benefit from calibration.

C. David Tobie