Battle Royale 4: Windows Phone 7 enters the ring

Editors' note: If you've already read "Battle Royale: Five smartphones face off", "Battle Royale 2: Smartphones face off, screen to screen", or "Battle Royale 3: The Final Conflict" (which, you know, didn't really pan out given the article you're currently reading), then you may experience some deja vu when reading this article. We've used the same tests and presented the article in the same style. Only the phones in question and the details of their performance have changed. Because of some technical difficulties on the back end, our "How we test: Smartphone displays" page (still!!) isn't up yet, but hopefully by Round 5 it will be.

I've now tested 12 different smartphone displays, including the two new ones presented today. Android and iPhone fans remain as passionate as ever about seemingly every aspect of their favorite phones, but now a new fighter enters the tournament. Today we test our first Windows Phone 7...um, phone. (I still have an aversion to the OS name.)

Once again, using DisplayMate Multimedia Edition for Mobile Displays, I put each phone through a battery of tests.

Well, today is a new day, and with that comes the promise of a more robust evaluation (or so the saying goes). For Round 4, not only do we have the iPhone 4, but also the HTC HD7, and the "="" rel="follow" target="_self">Konica Minolta CS-200 ChromaMeter to test the maximum brightness, black level, and contrast ratio of each phone and reported numbers for each of these three tests.

Test pattern screens: We used several DisplayMate Mobile test patterns to test for color-tracking errors, 24-bit color, and font legibility, among other things.

Real-world: We conducted real-world anecdotal testing using photos and 3D games.

All test screens were viewed within each phone's native gallery application. Some phones may handle pictures differently--and even improve them to some extent--outside the gallery application. That said, we believe that testing within the respective gallery applications is still a viable approach, as this is where most users will view pictures on their phones.

In order to diminish potential repetition, I'll dive right into the details of how each phone performed; if you'd like to know more about our tests, you can binge on nerdy details in our "How we tested" section at the bottom of this article. Please note that this is an evaluation of each phone's screen performance and nothing else. Check out the full reviews of these phones to determine which is right for you. Also, DisplayMate has posted a more technically focused evaluation of the iPhone 4 screens that's worth checking out.

The bottom line
Here's how we rank the phones in screen performance:

1. Apple iPhone 4
2. HTC HD7
3. Samsung Nexus S

Keep reading to find out why we ranked them this way.

I know everyone has strong opinions and usually fiery passions about their smartphones of choice, so I don't expect everyone to agree with my assessment or the methods used in drawing my conclusions. If there are any questions about how I came to my conclusions or anything relevant I may have left out, please leave a comment saying as much. This has become a regular feature here at CNET, so don't in any way believe this is the last word on the subject. We'll likely be seeing "Battle Royale 15: The iPhone 4 is dead, long live the iPhone 5D " at some point in the not too distant future.

Lastly, though I hope consumers get something useful out of this, I'd also be happy if the manufacturers of the phones took a serious look at these results and at least considered them when making their respective hardware and software revisions. We all want these phones to continue improving, and I'm just attempting to contribute to the cause.

Apple iPhone 4
The iPhone 4 was the best overall performer of the three phones we tested. The iPhone 4 was capable of displaying 24-bit color and was able to display colors in games and pictures with pop and life while still being accurate. The iPhone 4 won in most of our scientific tests and also had the best performance overall in our real-world tests. Once again, the iPhone 4 has the best smartphone screen on the market.

HTC HD7
The HD7 displayed mostly accurate color; however, the color did show evidence of being washed out in certain tests. Also, the phone's gallery app may have a bandwidth problem, which resulted in blurry text in our tests. We'll need to do more testing though to confirm.

Samsung Nexus S
The Nexus S saw an incredible contrast ratio thanks to its OLED screen. Also, it displayed fonts smoothly and legibly and passed the Coke can test with only minimal dithering. Unfortunately the Nexus S failed in most of our other tests, especially color tracking, white-level saturation, and false contouring. The Nexus S was the least impressive of the three.

How we tested
We measured each display's brightness, black level, and contrast ratio using the CS-200 and test patterns provided by DisplayMate. All phones were tested at their maximum brightness with full battery charges. All readings were conducted in a completely dark room.

"At least/At most" explanation: True black can be represented as 0 candelas per square meter (cd/M2). Thanks to its OLED screen, the HTC HD7's black levels were so low, the Konica Minolta CS-200 ChromaMeter wasn't equipped to detect them. According to its specs, the CS-200 can only see black-level measurements as low as 0.005 candelas per square meter (cd/m2). Using simple logic, we can infer that both phones achieved, at most, a 0.0049 cd/m2 black level. Using this method we were able to determine the estimated contrast ratio of the Nexus S.

Test patterns: All test-pattern tests were conducted in a completely dark room.

White-level saturation: This test includes a number of rectangular blocks on a bright, white background. Peak white is represented by the block labeled 255. The closer a screen gets to displaying 255, the more likely it'll be to show certain colors when displaying a really bright screen. The iPhone 4 came out on top here by just barely displaying up to level 254. The HTC HD7 also displayed up to level 254, just not as clearly. The Nexus S achieved no higher than 251, and it must be noted that it had some red tint problems where what should have been gray boxes looked pink instead.

Color scales: This tests the display's ability to show 25 distinct intensity levels for each of the 10 primary colors, from black to peak brightness. A perfect showing would have each color with 25 distinct steps. The Samsung Nexus S had the worst performance as its scaling from dark to light included several nonlinear jumps. Also, a few colors within a given color row were noticeably inaccurate. The HTC HD7 showed a linear progression from dark to light, but some of its steps had evidence of compression as some levels blended in with others and were not as distinct as they should have been. The iPhone 4 displayed the color scale linearly and accurately; however, it could not show the next to darkest level of the colors, indicating that very dark colors may be out of the iPhone 4's reach. Both the Nexus S and HD7 had no problem showing that level though.

Color tracking: This screen tests the LCD's capability to display the grayscale uniformly and accurately without any color tint problems. As in previous rounds, the iPhone 4 had the best presentation here with an accurate grayscale and no apparent color tint problems. The HTC HD7 also showed an accurate grayscale with no apparent color problems. The Nexus S had a very obvious green and red color tint problem and, like in the color scales test, its progression from dark to light was nonlinear and skipped around a lot.

RGBW smooth color ramp: This an excellent test for determining whether the LCD can display 24-bit color. If the scale is smooth, without visible steps, the display should be capable of 24-bit color. If not, it's likely limited to 16-bit, or possibly 18-bit, color. The Nexus S showed very visible steps and is likely not capable of 24-bit color, at least not in its gallery app. The iPhone 4 and HD7 each showed a smooth progression from dark to light and likely each supports 24-bit color.

Fonts: We tested black, gray, and white fonts on different combinations of black, gray, and white backgrounds. Depending on how the phone handles things, certain combinations may affect the text's legibility. The HTC HD7 delivered blurry text during our test. Our test photo has a resolution of 480x800, the same as the HD7's native resolution. Also, when viewing Websites and the phone's menu, we saw no signs of blurry text. It could be that the phone's gallery app just doesn't have quite enough bandwidth devoted to it, but we can't yet say that definitively without more testing. Text on the iPhone 4 was sharp, but thanks to its high resolution, was also small and difficult to see without squinting. The Nexus S delivered the best overall text, as it was properly sized and just as sharp as the iPhone 4's.

Real-world tests
Coca-Cola photo: A high-quality picture of a Coke can is useful for testing how close the phone can come to reproducing colors from the real world. We used a real Coke can as a reference. The iPhone 4 displayed the pic with the most accurate color, where red looked accurate and vibrant rather than washed out. The Nexus S was second best, with a detailed can with only a small amount of visible dithering; however, the color was oversaturated and the can's color appeared more orange-red than red. The HD7 showed no signs of dithering, but had washed-out color.

Mars photo: We used a picture of a sunset on Mars to test the display's real-world false contouring threshold. The sky should appear to smoothly transition in color. If visible steps are noticeable, the phone has a false-contouring problem. The iPhone 4 displayed the clearest picture with no false contouring signs, but it was too dark to see the darkest detail of the rocks on the bottom of the picture. The HD7 came in second with no false contouring, and more visible dark detail than the iPhone 4, but the overall picture was less clear. The Nexus S had very noticeable evidence of egregious false contouring in the sky, but dark detail was more visible than on the iPhone 4.

Game: We used Raging Thunder 2 on the iPhone 4, Raging Thunder 2 Lite on the Nexus S, and Need for Speed: Underground on the HD7 to evaluate each phone's color performance in a fast-moving game. Both the iPhone 4 and Nexus S delivered a bright and vibrant image; however, the Nexus S' color was not as accurate and was noticeably oversaturated. Not surprisingly, the HD7 showed somewhat washed-out color and a muted vibrancy.