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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Brian Klug - Wednesday, June 30, 2010 - link
You know, I realized that seconds after writing it and decided that it'd just be too much to go into a detailed explanation. I corrected it to something much simpler ;)-Brian
zerosomething - Wednesday, June 30, 2010 - link
Fantastic article thanks for the in-depth review.From the article on page 5. "...iPhone capacity markings have disappeared from the back of the phone - no doubt this was done so Apple could make one part and one part only for each color."
There is actually a Model number on the back of mine. So there will need to be 4 different backs. However they can make one part for each color for the fronts. In reality they will have to make 2 fronts and 4 backs to cover all capacities and colors which is one more than they had to make for the 3G/GS phones.
Wow I'm picking such tiny nits in a fantastic article. Guess everything else was so through this one stood out.
Shadowmaster625 - Wednesday, June 30, 2010 - link
If you already own an iPhone, how is it worth it to upgrade? You said so yourself... tiny text is still tiny. So what are you getting for hundreds of dollars that the 3GS doesnt give?Guspaz - Wednesday, June 30, 2010 - link
I'm a 3GS owner in Canada (Fido is my provider), so we've had tethering ever since iOS 3.0 launched roughly a year ago. I noticed two small errors in the discussion on tethering, and felt one thing was possibly mischaracterized.First, I'd like to give a brief mention of how tethering works with Fido (and other Canadian providers). We've always had data caps on our iPhone data plans. Typically, you get something vaguely like 1GB for $30, but both the 3G and 3GS launches featured limited-time 6GB for $30 offers that are permanently grandfathered.
Fido/Rogers policy is that all users with a 1GB dataplan or higher get free tethering (this appears to be a permanent position), which uses the same data cap. So, in effect, the vast majority of Canadian iPhone owners have tethering.
The first error is "With the iOS 4 upgrades the iPhone 4 supports tethering over Bluetooth or USB." Tethering is not new in iOS 4; it's been supported since iOS 3, and tethering support is identical in iOS 4.
The second error is "You also need to either have Bluetooth enabled or be connected via USB to the computer you wish to tether." Firstly, Bluetooth doesn't need to be enabled before enabling tethering. If you enable tethering while bluetooth is disabled, a prompt appears asking you if you want to enable bluetooth, or just tether over USB. Secondly, not really an error but an important clarification: on Windows, you can only tether via USB with a computer that has the iPhone tethering drivers installed.
These tethering drivers are bundled with iTunes, and cannot normally be installed separately, but iTunes and the drivers have separate uninstallers in Add/Remove Programs. This means that you can set up, say, a friend's laptop to tether via USB by installing iTunes and then uninstalling iTunes, leaving the drivers behind. Annoying, but workable if bluetooth is unavailable.
In terms of the mischaracterization, the performance of tethering is called into question. This may be an AT&T networking issue, as I've not experienced the performance issues. Generally, whatever the networking performance my phone is achieving, a tethered computer will also achieve. There is no difference between the two, so any connectivity issues are strictly network-related rather than tethering-related. Performance is generally good; latency is usually 130-150 to a close remote host, and downstream bandwidth is 1-5 Mbps depending on congestion/location. Upstream, since the iPhone 3GS lacks HSUPA, is limited (335Kbps in practical tests), but tends not to vary quite as much as downstream based on signal quality.
Upstream performance isn't stellar, but it is relatively reliable, if a tad slow. Packetloss is rare if the phone has a good signal. I regularly use tethering to get laptops connected on the road, and remote desktop over a tethered connection is very snappy, and is amazingly faster than on-device RDP.
Mike1111 - Wednesday, June 30, 2010 - link
@Anand:"Even if you just cover the camera it’s actually better to make calls over FaceTime than 3G based on the sound quality alone."
Cover the camera? Why? Just press Home and you have a traditional voice-only VoIP call with reduced bandwidth.
Also I would like to see some comparison to the competition. Video calling on phones exists for quite some time. How about a comparison of video and voice quality?
And in regard to the bandwidth requirements, would it have been realistic to allow FaceTime over 3G?
You also mention that the compression is too high for text, is that because of a bad compression algorithm or codec, too low resolution or bandwidth? Is that something that realistically could have been done better?
strikeback03 - Thursday, July 1, 2010 - link
Does returning to the home screen actually kill the camera? That would be annoying if you only wanted to look at your calendar or something else on the phone while in a video call.Mike1111 - Thursday, July 1, 2010 - link
As with a normal (cellular) call you can always resume the video by tapping on the green status bar (call active...).Oyeve - Wednesday, June 30, 2010 - link
How is the sound quality? Is there an EQ (missing from all things "i")bkman - Wednesday, June 30, 2010 - link
An interesting review but flawed by bad metrics. The authors confuse absolute power measurement, dBm, with relative power measurement, dB. For example, a signal strength drop from -51dBm to -83dBm is not a drop of 24dBm, it is a drop of 24dB.hgoor - Wednesday, June 30, 2010 - link
Hi, I loved the review: really (and mean really) thorough! Thanks for that.However: unless I blacked out while reading and missed it: what about the noise canceling microphone? How does that work? I guess it's not that noticeable as you only mention it one time?
I'm very curious to find out if it's a feature that helps? Also: I wonder if it can be used for listening to music? I have an expensive pair of headphones from Sennheiser, but I wonder if it can be used (in the future?) to help listen to music (and on/or on the phone) when you have a lot of ambient noise?
Would be nice if you could clear that up. Also: I wonder how the iPhone 4 holds up against the new Samsung 1ghz powerhouse?
Keep up the good work!