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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  • noiserr - Friday, July 2, 2010 - link

    I am getting really tired of people who have no clue what OS X actually is.

    Android is much more similar to OS X than Windows. OS X is based on an Open Source kernel for starters and both Android and OS X are *nixes, OS X also uses open standards (OpenGL vs. DirectX for instance).

    OS X is in many ways much more configurable and open than Windows, compare how many file systems Windows supports vs. those OS X does.

    Apple is foremost a hardware company. They strive to create tightly integrated devices which come at the price of less configurability but they are renowned for their intuitive UI and ease of use. You may disagree with it but you can't argue against the fact that It's a business model that has served Apple well.

    Personally I am a geek. I also write code for a living, while I do indeed like Android a lot when it comes to my phone I just don't care nor do I have time to tinker with it.
    Reply
  • Mr Alpha - Wednesday, June 30, 2010 - link

    "If there's one thing I hope the iPhone 4 display does, it's generate demand for 300 PPI level desktop displays - the era of 110 PPI displays being the norm needs to end now."

    Hear, hear!
    Reply
  • Griswold - Wednesday, June 30, 2010 - link

    I dont want ppi inflated desktop screens. Ive tried to work with them and they are an utter failure for me. Reply
  • Zan Lynx - Wednesday, June 30, 2010 - link

    I used to use a 150 DPI laptop screen. It was excellent.

    Blame your lousy desktop software, not the beautiful screens.
    Reply
  • fabarati - Wednesday, June 30, 2010 - link

    Haven't read through all of it yet, but the contrast part on the first page seems to be in the wrong place, or we're missing a whole section there. I'll add more stuff as I find them. Reply
  • fabarati - Wednesday, June 30, 2010 - link

    ok, on the first display page, you write "They're both entirely conventions." It may just be my non-native english speaking that's shining through, but that seems to be lacking a few words.

    And It's hard to know who's writing what. In one section, Brian's the third party, in another, it's anand. Especially when you're comparing things, it makes it a little hard to follow.
    Reply
  • fabarati - Wednesday, June 30, 2010 - link

    Some minor niggles, like videocalls already existing in other regions over 3G (and being hugely impopular), and not being sure about it being the best camera (comparisons to other phones than those listed are needed, like some nokia, sony ericsson and samsung phones), but otherwise a very thorough and fair review.

    Good job!
    Reply
  • Jittos - Wednesday, June 30, 2010 - link

    I've been sensing Anandtech's bias towards Apple's product for quite sometimes. Especially in cases where there are direct comparisons between iPhone and Android. However, I've always enjoyed the scientific/ fact-based method of tests Anandtech uses.

    Now please correct me if I misunderstood the article, but from what I'm reading in the signal strength comparison, it's iPhone 4 IN A CASE vs iPhone 3GS vs Nexus One? Why only test iPhone 4 in a case? Why not also show the results of iPhone without the case? I'm asking this so that we can all see how the iPhone 4 performs under various scenarios. Many iPhone users prefer to not put their beautiful device in a rubber case.

    IF Anandtech indeed intentionally omit the test results for iPhone without case just so that iPhone 4 can have good looking results, then I lose all respect I have for Anandtech as a professionally run tech site. (so please correct me that I'm wrong)
    Reply
  • Jittos - Wednesday, June 30, 2010 - link

    OK, I re-read the article and I was wrong. sorry.

    Anadtech is still the best :)
    Reply
  • piroroadkill - Wednesday, June 30, 2010 - link

    Yeah, don't be so hasty.

    This is easily the best, and most technical article I've seen on the antenna problem yet.

    It confirms it, and describes why people have varying experiences (the really, really non-linear bars.. my guess is those cutoff points WILL be changed in the next iOS build to mask the problem) and compares it reasonably to other devices, which do show the problem, but much, much less.

    I'd love to say this would silence everyone, but I know there will still be irrational people, who, in the face of decent research, will still argue their point with no basis at all.

    Thank you Anand. You do come across as gushing over Apple products recently.. but even so, this was a decent article.
    Reply

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