Apple iPhone 4S: Thoroughly Reviewed
by Anand Lal Shimpi & Brian Klug on October 31, 2011 7:45 PM EST- Posted in
- Smartphones
- Apple
- Mobile
- iPhone
- iPhone 4S
Improved ISP in A5
So we’ve been over the optical system and the sensor, but there’s another factor as well - image signal processing (ISP). It surprised me to see Apple bring this up on stage, but it’s a hugely important point to make, that the quality of images captured on a given platform depends on everything in the image processing chain. The A5 SoC includes an improved ISP over what was in the A4, and is referred to as the H4. You can watch the OS power gate the ISP and activate it when you launch the camera on console as well:
Oct 18 16:35:02 unknown kernel[0]
: AppleH4CamIn::ISP_LoadFirmware_gated: fw len=1171480 Oct 18 16:35:02 unknown kernel[0] : AppleH4CamIn::ISP_LoadFirmware_gated - firmware checksum: 0x0545E78A Oct 18 16:35:02 unknown kernel[0] : AppleH4CamIn::power_on_hardware
The changes include faster processing to accommodate an 8 MP sensor, and vastly improved white balance (which we will show later), and finally some face detection algorithms that work in conjunction with autofocus and autoexposure. I’ve also noticed that the A5’s ISP seems to have improved AF speed (it’s hard to measure, but it just seems much faster) and more importantly the framerate of the capture preview is much higher. I’ve included a small video showing just how much smoother the 4S looks than the 4, even on my 1080p60 camera (which YouTube then reduces to 30fps) the difference is noticeable.
When the ISP detects a face, it’ll paint a green rectangle over the region and run the AF/AE routine just like it would if you tapped to focus. Like all face detection algorithms, it’s decent but not perfect, and I saw the face detection rectangle come up while shooting pictures of pumpkins at a pumpkin patch (which was fairly repeatable on one pumpkin), and a few other random occasions. Apple claims their ISP will run face detection on up to 10 faces and balance AF/AE accordingly for the best exposure.
I mentioned that the camera application preview framerate is improved - which it is - but the camera application is also speedier. Word on the street is that camera application launch time was a significant focus for the 4S, and I set out to measure the difference over the predecessors cameras. Camera launch time is one thing that was singled out during the presentation, but another that can be measured is HDR processing time. I quit all tasks and launched the camera application fresh five times (from tapping camera to seeing the iris fully open), then averaged.
| Camera Performance Comparison | |||
| Property | iPhone 3GS | iPhone 4 | iPhone 4S |
| Camera Launch Time (seconds) | 2.8 | 2.3 | 1.4 |
| HDR Capture Time (seconds) | - | 4.9 | 3.2 |
| Working Distance (cm) | ~7.0 | 7.0 | 6.5 |
The result on the 4S is a bit behind Apple’s quoted 1.1 seconds, though it’s possible they were measuring after an initial launch, whereas I’m starting with the camera completely closed each time. Still, 0.3 seconds isn’t that far away from their own measurements. The 4S is almost an entire second faster at launching the camera app than the 4, and 1.5x faster at merging three images to HDR than the 4. I also decided to get a rough measure of working distance on the three cameras, or the closest an object can be to the camera and still be focused on.
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Davabled - Monday, October 31, 2011 - link
With Field test enabled, do numbers closer to zero indicate a better connection? (I'm referring to the numbers that replace the bars in the upper left corner)Anand Lal Shimpi - Monday, October 31, 2011 - link
Correct :)Take care,
Anand
Formul - Monday, October 31, 2011 - link
why the huge drop from iPad 2 to iPhone 4S in the GL benchmark pro? its only about 30% performance .... any explanation?Anand Lal Shimpi - Monday, October 31, 2011 - link
Because the number was incorrect :-P Fixed now :)Take care,
Anand
ZebuluniteX - Monday, October 31, 2011 - link
Great review as always Anand!In addition to the GL benchmark pro results Formul mentioned, I was also surprised to see the Motorola Droid RAZR for some reason do far better than other Gingerbread-based Android smartphones. It is listed as using different version of Android (2.3.5 vs 2.3.4 or older), but given that very similar results were shown between the iPhone 4S and Honeycomb-running Galaxy Tab 8.9 in your 'iPhone 4S Preliminary Benchmarks' article (where the 4S was a bit slower than the Galaxy Tab in SunSpider, and marginally faster in BrowserMark), I'm guess those are just mislabeled Galaxy Tab results. Is that the case?
Anand Lal Shimpi - Monday, October 31, 2011 - link
Thank you - be sure to thank Brian Klug as well, he really did the bulk of the heavy lifting here. I just popped in to talk about silicon and battery life.The RAZR numbers are what we ran at the RAZR announcement: http://www.anandtech.com/show/4981/motorola-droid-...
The improvement is likely due to an updated browser from Motorola. I included those numbers effectively as a placeholder until Ice Cream Sandwich arrives :)
Take care,
Anand
ZebuluniteX - Tuesday, November 1, 2011 - link
Ah, thanks for the clarification, I missed that article. Hmm, that's interesting that, apparently, Motorola "ported" Honeycomb or Ice Cream Sandwich's browser optimizations to Gingerbread (or at least I assume that's what happened)...I'm in the market for a smartphone, and while I was leaning towards the 4S since I already am in the Apple ecosystem via an iPod Touch 2G, before pulling the trigger I wanted to read the Anandtech take on it. The review was excellent as always - thanks again to both you and Brian!
Formul - Monday, October 31, 2011 - link
that was fast! i knew something was not right as there was no mention of this in the text :-)thanks for another great review, keep up the good work! :-)
zanon - Monday, October 31, 2011 - link
The article wrote "The expectation that Apple will always deliver more than just a hardware upgrade is likely what made Siri a 4S exclusive."While only time will tell for sure, it seems quite possible that graduated ramp up had a bigger role to play here. As you say, most of the heavy duty lifting for Siri is going on server-side, and in turn local processing needs aren't too bad. However, the natural flip side of that of course is that the server-side infrastructure is required for the service to work at all, and resources aren't unlimited there either. Even with it limited purely to 4S users, Siri still had some availability problems in the first few days as millions activated and tried to user it simultaneously. It's not hard to imagine what would have happened if every single one of the tens of millions able to upgrade to iOS 5 *also* tried to start using it immediately. Apple has built a huge data center and that's all well and good, but nothing substitutes for actual working experience when it comes to massive software services.
By limiting the initial rollout, Apple can do performance profiling, get an idea of average loads after initial "let's try it" dies down, and so forth. Staggering a rollout also means being able to plan for the general load rather then suffering the classic and well known double-bind of
A) Building for a peak load, and ending up being left with a lot of extraneous hardware that barely gets used.
B) Building for the average, then suffering from embarrassing and headline generating outages for a week or two.
It's true they could just decide to keep it 4S only, but given they are still selling the iPhone 4, and probably make plenty of profit on that now very mature device, I think there is a decent chance they'll roll it out to a wider audience down the road.
Also, a few typos:
Page 2:
I think the phrase is "pretty much par for the *course* for Apple..." rather then "par for the case".
Pg 9, WiFi:
"...newest WLAN, Bluetooth, and FM *cobo* chip" should I think be "combo".
Pg 15:
...4S, without a (big blank, presumably some sentence was supposed to go here?)
Pg 16:
"aren't simply *academical*" should be "academic".
Again, great review, thank you.
Anand Lal Shimpi - Monday, October 31, 2011 - link
That's a very good point, I will add it to the discussion. The sinister view is to assume Apple did it to differentiate, the balanced view takes into account infrastructure, which is exactly what you did here :)And thanks for the corrections :)