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
POST A COMMENT

270 Comments

View All Comments

  • Mike Wadner - Saturday, July 3, 2010 - link

    Well then you're in pretty bad shape. Anyone who considers Microsoft not far behind Apple has their head up their F**KING ass. May be a nice review but I have doubts about their overall knowledge of whats going on out there. Reply
  • websitetrafficchecker - Wednesday, February 5, 2020 - link

    If you want to check website traffic for free, visit https://seowebsitetraffic.net/check-website-traffi... Reply
  • jorpoka - Wednesday, June 30, 2010 - link

    People seem to making a big deal about the increased ram in iPhone 4, but I think it was almost required.

    The graphics chip shares memory with the system (just like in previous models) so you have to consider the fact that the screen resolution has increased by 4. How is the system going to deal with the higher resolution grahpics... the 512 MB of ram.

    For now not every application on app store uses the updated resolution, but as more and more apps are updated for iOS 4 and the retina display i think the additional 256 MB ram benefit will decrease.
    Reply
  • solipsism - Wednesday, June 30, 2010 - link

    The surprise wasn't that 512MB wasn't deemed needed, it was simply unexpected after the iPad with a higher resolution, faster processor and generally higher chance for more complex apps to run on the 8x larger display only being shipped with 256MB, like the 3GS, when 512MB was expected. On other words, if the iPad didn't get 512MB RAM, few expected the iPhone 4 being shipped just a couple month later to get it. Reply
  • John Sawyer - Thursday, July 1, 2010 - link

    Not higher resolution on the iPad, but more pixels (but we get your meaning). Reply
  • Snotling - Thursday, July 1, 2010 - link

    that's the point I'm trying to make since the iPad's release... it was not a planned product, it was ruched out just so they would not be assassinated by the press and the fanatics, my full conspiracy theory is on my blog:
    http://cyberpeste.blogspot.com/2010/01/letter-to-s...

    Now with the iPhone 4, we see what Apple was actually working on before rushing out the iPad and its a very good product. superior in every way to the iPad.
    Reply
  • tkoyah - Sunday, July 4, 2010 - link

    Um, the iPad wasn't rushed. The iPad project actually pre-dated that of the iPhone. But when it became aparent that this would be the perfect interface for a Phone, the iPhone project began, and was given a higher priority.

    I expect this first iPad wasn't given more RAM: a) to keep the price-point under $500 b) because there was no pre-existing iPad software, so having less memory available wouldn't break any apps.
    Reply
  • tipoo - Wednesday, June 30, 2010 - link

    The big deal is that the iPad, their tablet, has half the RAM of the phone they released shortly after. With a bigger screen and more pixels, people naturally would have expected the iPad to have the technological edge, but with only half the RAM of the iPhone that is not the case. Reply
  • AMDJunkie - Wednesday, June 30, 2010 - link

    Begins after this post. Reply
  • Zokudu - Wednesday, June 30, 2010 - link

    Wonderfully written article I love this line of high end smartphone articles you guys have been releasing. I love the quality of the writing at Anandtech.

    Just a few questions I have.
    Doesn't AT&T have a 5 year exclusivity deal for the iPhone meaning they would still have around 2 years remaining before an opposing carrier could offer the device?

    Also several of my friends with iPhones both 3G and 3GS constantly complained about AT&Ts coverage within New York and blamed the carrier. However several of them have gotten iPhone 4's and are reported fewer dropped calls if any at all. I have been using a Blackberry on AT&T's network for several years now and have had no issues with their coverage. Do you feel the dropped calls within hot spots such as New York should be blamed on the iPhone itself or the network?

    Also where do you feel that Windows Phone 7 fits into the future of smartphones. Do you envision it taking center stage against both iOS4 and Android or falling to the wayside such as webOS ended up doing?

    Once again thank you for the wonderful read and keep up the quality work.
    Reply

Log in

Don't have an account? Sign up now