Thursday, July 01, 2010, 05:20 pm
Apple's iPhone 4 Retina Display places first in lab testsThe new Retina Display Apple uses in iPhone 4 was compared against alternative screens used in competing smartphones, and Dr. Raymond Soneira, President of DisplayMate Technologies, has offered additional comments about the display comparison.
The test results, published by PJ Jacobowitz of PC Mag, compared Apple's iPhone 4 with the Motorola Droid X, HTC Droid Incredible and HTC EVO, looking at brightness, contrast, color depth, and color accuracy. Soneira commented on the lab results, which provide the first technical look at the performance of the iPhone 4 Retina Display.
The brightest display was on the iPhone 4, which at 536 cd/m² was found to be twice as bright as the OLED display of HTC's Droid Incredible. PC Mag said the Incredible measured a "weak 236 cd/m²," and that, "compared to the iPhone 4's display, the Droid Incredible is very difficult to view outdoors." Other models tested fell about in the middle.
After the results were published, Soneira added that "the iPhone 4 is 25 percent brighter than the iPhone 3GS, which was the previous record holder, so the iPhone 4 is now the brightness king for smartphones."
Explaining that "the difference between the darkest and brightest points on a display is known as contrast," PC Mag reported that iPhone 4 was just slightly better than the Droid X in terms of contrast radio, achieving 1097 vs 1071 on the Droid X. The HTC EVO "offers a little more than half the contrast of these two, just 649."
The HTC Droid Incredible achieves a much higher contrast ratio due to its OLED screen, so while its "not very bight, it can create extremely dark level of blacks which creates contrast that eclipses all of the competitionit measured a staggering 39,373," PC Mag reported.
Soneira added, "Steve Jobs promised a Retina Display Contrast Ratio of 800 and PC Mag measured 1097, 37 percent more than the Apple advertised spec. That's very impressive because you seldom ever see manufacturers conservatively understate their specs to that degree - but then see my widely reported (and often misquoted) comments on the iPhone 4 Retina Display, where it falls short on that spec. The iPhone 4 is a tremendous improvement over the iPhone 3GS, which only had a measured Contrast Ratio of 138. But note that the Motorola Droid remains the Contrast Ratio king of mobile LCDs with 1436, which I measured in our own DisplayMate Lab tests."
Soneira also said that, "while the iPhone 4 LCD has a significantly lower Contrast Ratio than OLEDs, which typically have Contrast Ratios of 30,000 or more, it's not particularly relevant for mobile displays because they are typically viewed under bright ambient lighting, where screen reflections of the surrounding ambient light are much greater than the display's own internal black level. The Contrast Ratio spec only applies for viewing in the dark. The iPhone 4's bright screen and low reflectance means that it delivers a much higher real screen image Contrast under typical ambient lighting than OLEDs, which are not as bright and have inherently higher screen reflectance than the iPhones. But in dark ambient lighting the OLEDs deliver outstanding Contrast."
Color depth refers to the resolution of color supported by both the display hardware and the operating system software. Of the screens tested, only iPhone 4 and the Motorola Droid X supply screens capable of 24-bit color (16,777,216 colors, which Apple calls "millions" and which Windows refers to a "true color"); HTC's hardware on the Incredible and EVO can only display 16-bit color (65,535 colors, which Apple calls "thousands" and which Windows refers to a "high color").
In their bundled software however, only the iPhone 4 actually displays 24-bit color. Android's photo application is crippled to only support 16-bit color, reducing the Motorola Droid X to the same performance as the Incredible and EVO, expressing color banding and jaggies due to their significantly lower color resolution.
In looking at color accuracy, PC Mag wrote that displays should reproduce "100 percent of the sRGB color gamut; no more, no less. Anything more means that the colors being displayed are oversaturated, or punchy. Anything less means that colors are being understaurated, or blah." It called the test "good measure of color accuracy."
The report said the Droid X screen was closest to the desired baseline of color reproduction, with just 6 percent undersaturation; EVO was also close with 10 percent undersaturation. iPhone 4 was undersaturated by 36 percent, a figure similar to previous test results of the iPhone 3GS, while the Droid Incredible was oversaturated by 37%.
Soneira said "the PC Mag lab test result that really surprised and disappointed me was the small iPhone 4 display color gamut, which is only 64 percent of the industry sRGB/Rec.709 standard color gamut that is necessary to obtain accurate color reproduction for videos and photos. As a result all iPhone 4 images will have colors that are somewhat under-saturated and on the weak side. The same was true for the iPhone 3GS and all previous iPhones and iPods. I was really expecting the iPhone 4 to correct that deficiency and perform as well as the Motorola Droid, an IPS LCD that matches the standard color gamut almost exactly and delivers essentially perfect color accuracy images, as good or better than most HDTVs. So the iPhone 4 is disappointing in color saturation and color accuracy, but is state-of-the-art in pixel resolution and sharpness.
"On the other hand, the PC Mag lab tests found that the HTC Droid Incredible had way too large a color gamut and color saturation, the same as the Nexus One and most OLED displays on many phones. While that often gets an initial 'wow' response even from reviewers who should know better too much image color and coloration in photos and videos is actually visually worse than too little color. So the iPhone 4's less than ideal weak color is actually visually better and preferable to all of those OLED displays that have excessive color unless you prefer gaudy colored images."
A reader added the comment, "the color accuracy (sRGB color gamut) of the iPhone is 'undersaturated' simply because higher saturation color filters on LCDs attenuate more light. Therefore, you need a brighter backlight behind a higher color saturation filter (e.g. R, G and/or B) to get the same light out of the front as compared with a lower saturation color filter. Since Apple was already taking a big hit on efficiency of the LCD assembly due to the high-resolution display, there was a trade-off made to use lower saturation color filters in order to obtain reasonable battery life in the device."
PC Mag reported "iPhone 4 has the most well-rounded display of our bunch. It offers a completely 24-bit color experience, the brightest screen, and great contrast (for an LCD.) The iPhone 4 could be even better if didn't Apple didn't limit its color accuracy."
It awarded Motorola's Droid X second place, while noting "the HTC Droid Incredible is the master of contrast, but its 16-bit display, oversaturated colors, and lack of brightness for outdoor viewing might turn some people off. The HTC EVO 4G, meanwhile, didn't excel at anything."
Soneira said DisplayMate Technologies will be reporting its own intensive lab tests on the iPhone 4 display, "with in-depth evaluations and analysis and some comments on how manufacturers can improve their mobile displays." The company produces display optimization, calibration, evaluation, and diagnostic products for consumers, technicians, and manufacturers, used by hundreds of publications worldwide for editorial reviews for every type of display.
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