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

285 Comments

View All Comments

  • philosofa - Wednesday, June 30, 2010 - link

    This kind of in-depth and insightful review is exactly why I read pretty much every Anandtech article (that and a liberal workplace when it comes to browsing lol). Cheers very much Brian & Anand. Don't feel a huge urge to upgrade from my 3GS, but it does look like a pretty damn fine smartphone! Reply
  • quiksilvr - Wednesday, June 30, 2010 - link

    Yeah, but he's holding it wrong :( Reply
  • medi01 - Wednesday, June 30, 2010 - link

    But guys, who do you pay a fortune for these phones? If you'd buy iphone or whatever phone with 2 year contract in most of Europe you'd pay just the price of the phone over 2 years (a bit more, in case of iphones it's about 700 Euro)

    I mean, aren't there cheaper contracts? I could imagine, that you can't buy some models other than from mobile providers, but hey, there are other countries with online shops.
    Reply
  • Snotling - Thursday, July 01, 2010 - link

    In north America and even more in Canada, there is a lot of territory to cover and lower population density. Cellular networks need to plant antennas where there is theoretically too few users to pay for it. Reply
  • JimmiG - Thursday, July 01, 2010 - link

    Sweden is kind of like a smaller version of Canada. Apart from the three major metro regions (Stockholm, Malmo and Gothenburg), the country is very sparsely populated. An average city is maybe 50,000 people. Yet we have extremely affordable plans by comparison.. I mean like less than $10 for a perfectly usable plan (1GB of data or so) and no more than $20 for 5GB or even Unlimited. Paying $100 a moth..geez. I barely pay that in a year. Reply
  • Ratinator - Friday, July 02, 2010 - link

    Sorry, I think that is a bad comparison.

    Sweden is 2/3rd the size of the province of Saskatchewan and 9 times the population of Saskatchewan as well. You can't even compare Sweden to the province of Saskatchewan let alone Canada. You have roughly 13.5 times the population density of that province. Mind you this is probably least densely populated of the provinces (not territories) Maybe not the best example, but lets look at a better one.

    You could maybe compare to Ontario (our most populated province) however, you are less than half their size with 80% of their population. When calculated out you still have almost twice the population density of our most populated province.
    Reply
  • ABR - Monday, July 05, 2010 - link

    It's pretty hard to find countries with similar population density to Canada, ranked 228 out of 239 in the world according to wikipedia. On the other hand, most of the country is inaccessible by road and I seriously doubt you are putting up cell towers in Nunavut. On the other hand Finland has half the population density of the United States and yet has similar cellular and broadband rates to Sweden. We don't know what it is with North America, whether a lack of competition, cartel agreements, or all the companies being weighed down by historical investments, but you guys do lead the world in what you pay for communications. Reply
  • Guspaz - Wednesday, October 12, 2011 - link

    According to the CIA world factbook (yes, I use a foreign agency's site for info on my own country), 90% of Canada's population lives within 160km of the US border.

    If we make an estimated measurement and take the southern border's length at 6416 km, multiply that by 160 and you get an area of about a million square kilometres with a population of, adjusting for the 90%, about 31 million. That would be an actual density in that region of about 31 people per square kilometre.

    That puts us in 180th place, right behind the US in 179, which has a density of 32. This is close enough to say that, within our populated region, we've got about the same population density as the US.
    Reply
  • ripwell - Saturday, July 03, 2010 - link

    Are you comparing data plans to voice and data plans? Telia was blasted when the iPhone first came out with some of the most expensive plans in the world. It's pretty amazing if you're suggesting that you can now get voice and data for just $10 a month. Reply
  • JimmiG - Sunday, July 04, 2010 - link

    "It's pretty amazing if you're suggesting that you can now get voice and data for just $10 a month. "

    You rarely get pre-paid minutes here unless you really want to. You just pay about $6 a month and get billed for your minutes afterwards. In my case, it's about 10¢ per minute, but to phones on the same network, you get unlimited texts, mms's and minutes. Yes, for $6 a month. That includes most of my friends and relatives that's pretty much what I pay for voice and texts.

    Then on top of that, you can add your data plan, for example 1GB a month at 6Mb is $9 (add $7.8 for 5GB at 10Mb/s).

    -Or, if you really must go crazy, you can get 3,000 minutes for $65. Combined with 5GB/month at 10Mb/s, you're paying roughly $82. That's the absolute maximum. No subsidized phone, but you get over 3x more minutes than the iPhone deal and 2.5x the amount of data. The phones aren't really subsidized at all when you look at the total cost.

    "You could maybe compare to Ontario (our most populated province) however, you are less than half their size with 80% of their population. When calculated out you still have almost twice the population density of our most populated province. "

    But what about the US? Its population density is 32/km2 vs 20.6/km2 for Sweden. There are definitely states that are comparable in size and population density.
    Reply

Log in

Don't have an account? Sign up now