Apple's iPhone 4: Thoroughly Reviewed
by Brian Klug & Anand Lal Shimpi on June 30, 2010 4:06 AM EST- Posted in
- Smartphones
- Apple
- iPhone 4
- Gadgets
- Mobile
Welcome to 2010, Apple Upgrades its Camera
The iPhone 4 is equipped with two cameras: a 5 megapixel camera with LED flash on the back of the phone and a VGA camera with no flash on the front. The LED flash works in both still and video modes. Like the EVO 4G, the iPhone 4‘s flash allows you to shoot in perfect darkness. If you’re filming a video in low light the LED will stay illuminated while you’re recording.
Taken with the iPhone 4 in total darkness
The same unfortunately can’t be said for the front facing camera on the 4. In anything but good lighting you’re going to get noise. It’s really only useful for FaceTime (or as an alternative to a mirror) and even then you need to be well lit for it to look decent.
Apple has opted for a 5 megapixel OmniVision sensor for the rear camera on the iPhone 4. What's interesting is that Apple has decided to bring backside illumination front and center with their marketing.
Backside illumination improves the sensitivity of CMOS and CCD detectors by reducing the amount of material in the path of incident light. In a frontside illuminated detector, a considerable amount of light is lost due to absorption that doesn't result in emission of an electron, in addition to reflection off pixel structures and electrical components near the frontside surface. Backside illumination greatly improves sensitivity by flipping the stack over. Instead of light having to pass through and possibly be reflected by metal structures, it is converted into electrons and read out by passing solely through silicon. Creating a backside illuminated part isn't as simple as flipping a sensor over, however, as manufacturers also generally thin the silicon light has to pass through before it can reach the photodiode. This further improves sensitivity and is generally accomplished through chemical etching in acid or by lapping (physically grinding) sensors at wafer scale.
OmniVision OV5650 - iPhone 4's rear camera SoC
Though backside illumination (BSI) improves quantum efficiency (how many photons are converted into electons), backside illumination is hugely important for another serious reason as well. Because the sensor is small at 4.6 mm by 3.4 mm, pixel size is also extremely small at just 1.75 microns square for the OV5650 in the iPhone 4 (state of the art sensors are 1.4 microns square, like those in the HTC Incredible's 8 MP sensor). Frontside illuminated parts generally have in the neighborhood of 10-15 microns of silicon before the active region of the photodiode where one wants photons to get converted to electrons. The result is that without backside illumination, pixels have a 10:1 ratio of height to length, you can visualize them as looking something like long square pillars. But that's a problem.
As photons are converted into electrons in that silicon, there's no guarantee that it will immediately travel down into the gate structure below to be read out by the camera. Electrons drift as they descend these columns, meaning that photons incident on one pixel don't necessarily map to the gate below. Because the smartphone camera sensors are so small, with a 10:1 ratio of height to size, the result is large amounts of so-called quantum blurring from electrons traveling into the gate structures of adjacent pixels. The result is a blurry image (and a decrease in MTF at the sensor level!), thus not representing the image that used to be incident on the sensor.
OmniVision and other smartphone CMOS sensor manufacturers thin that column down in an effort to come closer to having the pixel look more like a cube than a huge pillar. Ballpark numbers are between 3 and 6 microns, down from 10-15. The result is much more sensitive sensors that are higher resolution. While megapixels don't necessarily matter, neither does pixel size as much anymore; it's all about quantum efficiency, which is what engineers really care about.
OmniVision BSI - Courtesy OmniVision
The optical system of the iPhone 4 is difficult to characterize without disassembly, though the focal length is a bit shorter than previous iPhones. The result is that the photos are demonstrably wider angle. Backside illumination also allows for a bigger chief ray angle, higher numerical aperture (and thus lower f/#), but I won't bore you with the details.
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Lemurion - Friday, July 2, 2010 - link
I was disappointed that you they only compared the iPhone 4 screen to the 800 by 480 AMOLED screens on some of the Android devices. As far as I know, all those devices use the Pentile system, which reduces the crispness of text.I would have really liked to compare the new Apple screen to the Motorola Droid's 266 PPI screen and see how noticeable the difference there was.
Matt Campbell - Friday, July 2, 2010 - link
Nice investigation work on the signal strength. Just wanted to point out that AnandTech is cited in the Apple iPhone 4 software fix story on CNN today. http://www.cnn.com/2010/TECH/mobile/07/02/apple.ip...Bad Bimr - Friday, July 2, 2010 - link
http://www.cnn DOT com/2010/TECH/mobile/07/02/apple.iphone.apology/index.htmlJust like apple, finally admitting a problem, pleasing the fan boys by saying it will be addressed and doing nothing to fix it. I am so glad I never jumped on the apple bandwagon.
fischerm83 - Friday, July 2, 2010 - link
So i was reading various news articles today and saw that apple finally figured out/admitted to what you guys found out earlier this week...*quote*
Now the company says its engineers have made a "stunning" discovery. Reception is poor and calls may be dropped because not only are people holding the phone wrong, but they also think they have a better signal than they do. In the statement, Apple says that it has made a mistake in the formula that calculates the number of bars that display the signal strength on all of its iPhones.
"We were stunned to find that the formula we use to calculate how many bars of signal strength to display is totally wrong," it said in a statement.
*quote*
Full Article:
http://news.cnet.com/8301-30686_3-20009564-266.htm...
Nice work guys, keep up the amazing work!
anandreader - Friday, July 2, 2010 - link
Brian-I'm confused as to what had to happen to get Fieldtest onto the iphone 4. Understood the bit about jailbreaking the iphone3 but didn't understand how that information got transfered to the 4.
Could you elaborate a bit there?
Per Grenerfors - Friday, July 2, 2010 - link
Thanks for the great review, AnandTech.In countries where 3G coverages isn't spotty like a teenagers face, the whole antenna/at&t/verizon debate is just utterly unnecessary.
Apple is the only brand name in tech today that's recognized by the broader public. Their products therefore make a big splash in the media when they hit the market. But the bigger splash you make, the more mud comes floating up from the bottom. Like people complaining with a spec sheet in hand without ever having seen the device in real life. Or just plain old haters. This is the downside to fame. But I'm sure Apple's laughing all the way to the bank.
Stokestack - Friday, July 2, 2010 - link
A case isn't an acceptable workaround for this. I don't buy a thin phone to bulk it up and junk it up with a cheesy case or add-on of any kind.While I'm not planning on getting an iPhone 4, if I had one and wanted to keep it I'd try to spray a coating onto the antenna band. I'd mask the front & back, the buttons, and any seams, then spray with polyurethane or something. While it would be microscopically thin, there's be no direct contact with skin. And really, that's what you said you expected Apple to have done anyway. Let's see if it would work.
Excellent review. The hack to get the numeric signal strength rocks.
Fulle - Friday, July 2, 2010 - link
Thank you for the review. It was useful to be able to look at something that was detailed, and included facts, good and bad, without a ridiculous amount of bias. It's obvious that Anand likes, or at least really wants to like most Apple products, but it was nice that that didn't get in the way of the review.The new iPhone seems to be an OK device that's on par with new Android smartphones in way of hardware... The screen's got 20% higher pixel density than the Droid, but 50% worse contrast ratio, and worse black quality... Java performance is clearly inferior to a Nexus One, but browsing performance is competitive (I'd say good, but I think all handsets have shit browser performance). Its sleak and thin, but it has no hardware qwerty. The 5MP camera produces low noise, but, the white balance is messed up, making it overall inferior to the camera in a Nexus One or HTC Incredible (or Moto Droid, even, IMHO... screwed up over-saturated colors with bad white balance are a big deal to me). Overall, it's an average device when put up against worthy competition (EVO4G, DroidX, HTC Incredible, Nexus One, or even a Moto Droid).
But, that's before you have to deal with the obvious design flaws. Glass panels on both sides? WTF? Uninsulated external antenna? These aren't minor flaws here.
So, overall I'd say that the new iPhone is inferior to at least 6 Android smartphones.... and at first I grin at that... but then I'm disappointed and mad. Apple has helped make the smartphone market the competitive environment it is today, and when they drop the ball like this, it means that other venders don't have to raise the quality of their devices to compete. It's just fortunate that Android has so many hardware OEMs, like HTC, Samsung, and Motorolla, all competing with each other... or else I'd be afraid the only thing the iPhone4 would push in competition is a higher ppi on the screens.
Lets hope this helps push the Cortex-A9 equipped Android's this winter to include higher resolution in their displays... but, man, I'm disappointed with this device.
tgibbs - Friday, July 2, 2010 - link
Does zero dB represent a standard absolute signal strength or is it an arbitrary reference value that will differ for different phones?navderek - Saturday, July 3, 2010 - link
The signal is actually measured in dBm which means it is a reference to 1mW of power.For example -30dBm = 1000 times less that 1mW = 1uW
1 microwatt does not seem like much, but actually this is a very strong signal for the mobile and you would rarely have that much power arriving at your handset from the tower. In good conditions, close to the tower or serving antenna with minimal obstructions you could expect about -50 to -60 dBm (-60dBm = 1nW (nanowatt). The system is designed to deal with such small signals...this is why I laugh when people are worried about cell tower "radiation" when actually 5 min. in the sun is a bazzillion times more radiation than what's coming out of a tower....cellular towers that is, broadcast radio towers or paging systems are another story!
But I digress...to answer your question simply, zero dBm simple equals 1mW.
Zero dBm signifies that there is no difference in ratio from the reference of 1mW.