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.

The Display in the Sun Camera Usability
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  • The0ne - Wednesday, June 30, 2010 - link

    Actually, Anand likes the performance of the iPhone and i don't blame him. It is smooth, well implemented and thus makes using it more enjoyable, quantifiable or not. Features be damn, what counts is how a user perceives the device he/she is using. And once attached or rather use to them it's hard to like something that isn't the same or better.

    For the most part, android OS and WebOS are fine for the vast majority of users. The slight sluggish performance is really not hindering anyone from doing anything practical. It is really just a matter of perception.

    As for features and design, I can honestly say unless you been in the design phase yourself many decisions are made prior to production. Missing features such as Flash memory support is a choice left out purposely. Don't kid yourself they are doing it because they either can't or because of lack of money/resources.
    Reply
  • mesiah - Thursday, July 1, 2010 - link

    I don't agree with the flash memory support. Flash memory is so cheap to implement that it comes on the cheapest of cheap products. And before anyone uses the excuse of "a flash port would clutter up the phone and make it look ugly" Look at the huge ugly connector port used to sync / dock an iphone. Compare that to micro usb. You don't think they could shrink that thing to a quarter of its current size, or less, and add in a flash memory port? Hell, A smart engineer could make a docking port that doubles as a flash memory port (makes me wonder why we haven't seen this yet.) The reason you don't get upgradeable flash memory is the same reason you don't get removeable batteries. There isn't money in batteries and memory, the money is in forcing people with outdated hardware to upgrade. Reply
  • The0ne - Thursday, July 1, 2010 - link

    Err, I think u might has misread what I was trying to say. As you've stated flash memory support is very easy and cheap to design in. For Apple not to have it means they have purposely decided against it. For example, creative labs has flash support on some of their PMP devices but it is extremely poor in design that it's unusable. That's the other caveat to just putting features in and not properly supporting it. Reply
  • Anand Lal Shimpi - Wednesday, June 30, 2010 - link

    By feature parity I was referring to what's new that made it into iPhone 4: higher res screen, 45nm SoC, much improved battery life, smaller form factor. I'd expect that within the next 6 - 12 months we will see Android phones with similar specs.

    Software feature wise, Android is at parity in most cases and far ahead in others.

    Take care,
    Anand
    Reply
  • darwinosx - Wednesday, June 30, 2010 - link

    They you don't know much about either Android, the iPhone 4, or both. Reply
  • Mumrik - Friday, July 2, 2010 - link

    Are you aware that your username undermines every single pro Apple comment you make?

    Also, I think most of us will take Anand's word for it over an anonymous commenter's.
    Reply
  • mmike70 - Sunday, July 4, 2010 - link

    Why does it undermine? Reply
  • John Sawyer - Thursday, July 1, 2010 - link

    The somewhat larger number of pixels in the Retina display that Apple is using in the iPhone 4, plus its smaller size than the Evo and Droid X displays, do combine to make for a massive difference, as the pictures in the article show. I've compared the two, and the iPhone 4 display really is startlingly good. Many things don't look hugely different between the two, such as some videos, larger graphics and text, etc., but small text (which I look at a lot because that's what a lot of websites serve up) certainly does. Reply
  • semo - Wednesday, June 30, 2010 - link

    I'm sorry Anand but I just couldn't bring my self to read your review after yet again detecting your bias towards this product. You come from an engineering background and it shows in your methods of analysis which appeals to me.

    Do you wait 6 hours in line for a new SSD? I detect hints of emotion in this article's introduction. I could be wrong but I always try to avoid technical reading when I suspect there is bias. It is plain to see on other technical sites where the companies' mission statement is part of the introduction but much more subtle here.

    I look forward to your next SSD and chip architecture articles.
    Reply
  • bplewis24 - Wednesday, June 30, 2010 - link

    Anand is about the most objective Apple iPhone fanboy there is. There is no denying this, and it's both a compliment and a criticism. Until he can stop making subjective generalizations like this:

    "There is this more open, more configurable, more capable feel you get with Android that you don't with the iPhone. That can be both a positive and a negative. Android phones feel more like computers while iPhones have more of that appliance feel. It still boils down to personal preference, the 4 won't change that."

    Really, Anand? Being more open and configurable can be a bad thing? We really need to stop perpetuating this myth that Androids can only be liked by "PC" geeks and people who like to dig deep into the OS. The reality is that Android devices don't force you to customize if you don't want to.

    I'm also fairly certain that the "scrolling" issue which isn't present on my Moto Droid has something to do with the live wallpapers eating up CPU processing power. Nevertheless, I don't experience it on my phone and to blanketly imply that the OS UI is clunky (which most iPhone fanboys cling to in every comparison) is completely disingenuous.

    Until Anand can rid himself of some of this bias, he will still be known as the best and most objective iPHone reviewer on the interwebs, but the title in and of itself won't be saying very much.

    Brandon
    Reply

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