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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metalev - Saturday, July 3, 2010 - link
I ploted the signal-strength-to-bars mapping for both Android and the iPhone 4 on the same axes:http://www.metalev.org/2010/07/android-vs-iphone-4...
This shows that the iPhone 4 consistently reports a higher percentage signal strength (as defined by the fraction of bars lit) than Android GSM devices at the same signal strength.
R. Johnson - Saturday, July 3, 2010 - link
I don't understand how Apple (Iphone4) can say the antenna issue is a math problem when I can sit here with all full antenna bars and then hold the phone with my left hand and get only half a bar within 15 seconds. I don't know what to trust anymore when Apple decides to use different math and different bars in an upcoming update. I am afraid they may now use different bars to have it APPEAR there is better reception than there really is.R. Johnson
SunSamurai - Saturday, July 3, 2010 - link
You better hurry and put on the tinfoil hat too.Give me a break. The article already pointed out it was a simple error in how the bars were representing signal. The actual numerical signal is actually better. They basically did the opposite of what youre freak'n out about.
navderek - Saturday, July 3, 2010 - link
@SunSamuraiPlenty of reason to freak out. This is a very obvious design flaw that has been overlooked by Apple, and now denied by Apple. I am an RF Engineer and when I watched the Apple keynote presentation of the device I almost fell off my chair when he presented the antenna design...Then I thought, no it must have a light coat of something to shield the antenna....guess not.
Apple is making profit hand over fist and paying sweatshop workers pennies to put these things together...the least they could do is provide free bumpers. No they won't though because they will open the door to legal issues...who cares, they can afford the legal costs and it would save their face and allow them to continue unscathed...Now they just look like any other greedy company out there. They've really lost there magic IMO. It's discouraging that profits > honor. They are a real good company and this will really hurt them.
StormyParis - Saturday, July 3, 2010 - link
The article is very nice, but the conclusion lets us down and not gently by falling into the fanboi worldview. I'm neither an Apple nor Android nor Palm fanboi. I recently bought an HD2, and I'm definitely NOT an MS fanboi. I just wanted the biggest possible screen, and the HD2's is 40% bigger than the iPhone's... it's not about resolution, but size: I'm getting old.If the Dell Streak had been out in my country, I'd probably have gotten it instead. If palm had a big-screen, keyboardless phone, I'd have strongly considered it, seeing that right before the HD2, I was still using my Palm TX because it just works.
Right now I wouldn't consider Apple because it's too closed, and too cumbersome to get content onto (iTunes crapped out on my PC every time I tried it). I'm not sure I could get winhttrack'ed sites onto it.
I think most phones have reached the point of "good enough". On mine, I'm using a browser, an ebook reader, a media player... and that's about it. I don't game, I don't do social web things, I don't need a fashion accessory/personality crutch...
SunSamurai - Saturday, July 3, 2010 - link
You sound bitter. Tell us where the iphone/droid touched you.btharms - Saturday, July 3, 2010 - link
My phone drops from 5 bars to 1 bar frequently. The way I comfortably hold the phone covers the black strip more often than not. I have run speed test after speed test, and what I have found is that while covering the strip, my 3g connection will drop to 0kbps! I can literaaly freeze safari while loading any web page by temporarily placing my finger on the black strip (it will continue to load a second or two after I remove my finger).I was achieving download speeds of around 1600 kilobits/sec with the phone in my hand without covering the black strip. When redoing the test while holding the phone normally (with my pinky finger covering the strip) the speed dropped as low as 0 (100 kilobits per second was the fastest). Actually, many times the test would not start until I removed my pinky from the spot. Then, after the test began I would softly place my pinky back on the strip - and instantly the speed drops near 0.
So as thorough as your testing was, realizing that the phone misrepresents signal strength is really not a pertinent issue when you consider that the 3g signal virtually dissapears immediately on contact with the black strip.
I'm basically demanding that apple comps me a free bumper or i'm returning my phone.
navderek - Saturday, July 3, 2010 - link
The main point is that by Apple redoing the math on the signal bars...it will have no effect on the issues your seeing. Bars don't man a thing. Real life means everything and if the call drops with 5 bars or zero bars it does not matter - the call still drops!THIS IS JUST A STUNT BY APPLE TO PUT THE BLAME ON THE CARRIERS...OPEN YOUR EYES PEOPLE. Once the SW update happens then people will go back to complaining about AT&T and others...just like Apple wants it.
Thing is, poeple aren't as dumb as Apple thinks. But I guess this is the most financially obvious thing for Apple to do. Shift the blame, it's not our problem!
Mike Wadner - Saturday, July 3, 2010 - link
I started reading your review and stopped immediately upon seeing this statement: Apple has real competitors in the smartphone space. Android phones have grown in features, polish and popularity. Even Palm entered the race with a competant offering, and Microsoft isn't far behind.What cave have you been in for the last year? Do you not have a F**KING clue what Microsoft just did with their phone this week - THEY ARE MILES BEHIND EVERYONE IN HARDWARE AND SOFTWARE. My 13 year old kid wouldn't even make a statement this stupid.
Microsoft is stillborn when it comes to mobile. To even consider Microsoft a worthy competitor in the smart phone area is insane.
You're credibility just went down the crapper with that statement.
navderek - Saturday, July 3, 2010 - link
Agreed...the review may be good to the laymen, but for others not so much. I highly respect Anandtech's reviews but this is really the first one I've seen where they seem to have done the review just to get some of that Apple limelight without actually asking the tough questions like why Apple went and designed the antenna like this? What is the link between this poor antenna design and the sudden sale of bumpers by Apple? hmmmmmm