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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robco - Monday, October 31, 2011 - link
I've been using the 4S from launch day and agree that Siri needs some work. That being said, it's pretty good for beta software. I would imagine Apple released it as a bonus for 4S buyers, but also to keep the load on their servers small while they get some real-world data before the final version comes in an update.The new camera is great. As for me, I'm glad Apple is resisting the urge to make the screen larger. The Galaxy Nexus looks nice, but the screen will be 4.65". I want a smartphone, not a tablet that makes phone calls. I honestly wouldn't want to carry something much larger than the iPhone and I would imagine I'm not the only one.
Great review as always.
TrackSmart - Monday, October 31, 2011 - link
I'm torn on screen size myself. Pocketable is nice. But I'm intrigued by the idea of a "mini-tablet" form factor, like the Samsung Galaxy Note with it's 5.3" screen (1280x800 resolution) and almost no bezel. That's HUGE for a phone, but if it replaces a tablet and a phone, and fits my normal pants pockets, it would be an interesting alternative. The pen/stylus is also intriguing. I will be torn between small form factor vs mini-tablet when I make my phone upgrade in the near future.To Anand and Brian: I'd love to see a review of the Samsung Galaxy Note. Maybe Samsung can send you a demo unit. It looks like a refined Dell Streak with a super-high resolution display and Wacom digitizer built in. Intriguing.
Rick83 - Wednesday, November 2, 2011 - link
That's why I got an Archos 5 two years ago. And what can I say? It works.Sadly the Note is A) three times as expensive as the Archos
and B) not yet on Android 4
there's also C) Codec support will suck compared to the Archos, and I'm pretty sure Samsung won't release an open bootloader, like Archos does.
I'm hoping that Archos will soon release a re-fresh of their smaller size tablets base on OMAP 4 and Android 4.
Alternatively, and equally as expensive as the Note, is the Sony dual-screen tablet. Looks interesting, but same caveats apply....
kylecronin - Monday, October 31, 2011 - link
> It’s going to be a case by case basis to determine which 4 cases that cover the front of the display work with the 4S.Clever
metafor - Monday, October 31, 2011 - link
"Here we have two hypothetical CPUs, one with a max power draw of 1W and another with a max power draw of 1.3W. The 1.3W chip is faster under load but it draws 30% more power. Running this completely made-up workload, the 1.3W chip completes the task in 4 seconds vs. 6 for its lower power predecessor and thus overall power consumed is lower. Another way of quantifying this is to say that in the example above, CPU A does 5.5 Joules of work vs. 6.2J for CPU B."The numbers are off. 4 seconds vs 6 seconds isn't 30% faster. Time-to-complete is the inverse of clockspeed.
Say a task takes 100 cycles. It would take 1 second on a 100Hz, 1 IPC CPU and 0.77 seconds on a 130Hz, 1 IPC CPU. This translates to 4.62 sec if given a task that takes 600 cycles of work (6 sec on the 100Hz, 1 IPC CPU).
Or 1W * 6s = 6J = 1.3W * 4.62s
Exactly the same amount of energy used for the task.
Anand Lal Shimpi - Monday, October 31, 2011 - link
Err sorry, I should've clarified. For the energy calculations I was looking at the entire period of time (10 seconds) and assumed CPU A & B have the same 0.05W idle power consumption.Doing the math that way you get 1W * 6s + 0.05W * 4s = 6.2J (CPU B)
and
1.3W * 4s + 0.05W * 6s = 5.5J (CPU A)
metafor - Monday, October 31, 2011 - link
Erm, that still presents the same problem. That is, a processor running at 130% the clockspeed will not finish in 4 seconds, it will finish in 4.62s.So the result is:
1W * 6s + 0.05W * 4s = 6.2J (CPU B)
1.3W * 4.62s + 0.05 * 5.38s = 6.275J (CPU A)
There's some rounding error there. If you use whole numbers, say 200Hz vs 100Hz:
1W * 10s + 0.05W * 10s = 10.5W (CPU B running for 20s with a task that takes 1000 cycles)
2W * 5s + 0.05W * 15s = 10.75W (CPU A running for 10s with a task that takes 1000 cycles)
Anand Lal Shimpi - Monday, October 31, 2011 - link
I wasn't comparing clock speeds, you have two separate processors - architectures unknown, 100% hypothetical. One draws 1.3W and completes the task in 4s, the other draws 1W and completes in 6s. For the sake of drawing a parallel to the 4S vs 4 you could assume that both chips run at the same clock. The improvements are entirely architectural, similar to A5 vs. A4.Take care,
Anand
metafor - Tuesday, November 1, 2011 - link
In that case, the CPU that draws 1.3W is more power efficient, as it managed to gain a 30% power draw for *more* than a 30% performance increase.I absolutely agree that this is the situation with the A5 compared to the A4, but that has nothing to do with the "race to sleep" problem.
That is to say, if CPU A finishes a task in 4s and CPU B finishes a task in 6s. CPU A is more than 30% faster than CPU B; it has higher perf/W.
Anand Lal Shimpi - Tuesday, November 1, 2011 - link
It is race to sleep though. The more power efficient CPU can get to sleep quicker (hurry up and wait is what Intel used to call it), which offsets any increases in peak power consumption. However, given the right workload, the more power efficient CPU can still use more power.Take care,
Anand