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.

Camera Improvements Still Image Capture Quality
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  • thunng8 - Wednesday, November 2, 2011 - link

    Subjectively similar, but if you read the detailed analysis, the iphone4S camera is sharper even without resorting to a high level of software sharpening. Reply
  • steven75 - Friday, November 11, 2011 - link

    Hardly anyone bought an iPhone 4 for facetime. That's very different from what's happening with Siri, whether it stays that way long term or not. Reply
  • doobydoo - Friday, December 2, 2011 - link

    Where's your evidence that the CPU in the Samsung Galaxy S2 is faster?

    Apple aren't using the same chip, they're using their own custom version of it.

    The CPU/GPU combination in the iPhone 4S is faster, full stop.
    Reply
  • kepler - Monday, October 31, 2011 - link

    I disagree, there were plenty of review for Android phones, as they come out. He did the Incredible and Thunderbolt pretty thoroughly. The difference is that he can't review 15 Android phones from 5 different manufacturers every month.

    I'm sure we'll get a great spread on the Galaxy Nexus, and possibly the Razr, as they are big ticket items. I know I pretty much just skim the Apple stuff, as I'm not a big fan of Apple, its practices of litigation over innovation, not to mention the moral distaste of Mr. Jobs. I think iOS is a child's OS, behind the times as it is, and Siri is just a gimmick to try to keep the outdated OS alive for (hopefully) its last iteration.

    Of course, none of that means that it isn't a good product.
    Reply
  • doobydoo - Tuesday, November 1, 2011 - link

    'iOS is a child's OS'

    Just like Google is a child's search engine.

    As Einstein said, everything should be as simple as possible, but not simpler.

    Usability matters.
    Reply
  • KoolAidMan1 - Monday, October 31, 2011 - link

    In what universe is hardware or practical OS performance faster with Android?

    Your bias, keep an eye on it.
    Reply
  • medi01 - Tuesday, November 1, 2011 - link

    In what universe did you have a chance to compare (legit) OS performance on the same hardware, you clown? Reply
  • doobydoo - Tuesday, November 1, 2011 - link

    Huh? In what universe could you not understand a basic sentence?

    He didn't say he'd measured two different OS's on the same hardware. He essentially said he could compare the REALITY of both sets of phones (Android and iOS) by taking into account their PRACTICAL performance, that being performance taking into account BOTH the hardware they run on and the software they run on.

    In other words, in the real world, iPhones DO use iOS, and Android phones DO use Android, putting one OS on the other hardware (which you are suggesting) would be completely irrelevant. What is relevant, however, is how they both ACTUALLY perform, given the reality of their software. And that has been measured throughout this article and shows the iPhone 4S is currently the best performing phone there is.

    Even taking the software aside, direct comparisons have been made between the Mali-400 in the SG2 and the much faster 543 in the iPhone 4S.
    Reply
  • claytontullos - Monday, October 31, 2011 - link

    I feel as though the throughput difference between ATT and Version/Sprint isn't being leveraged enough.

    I would really like you guys to review the Samsung Galaxy Note paying special attention to if it bridges the gap between tablet and phone.

    -
    Clayton
    Reply
  • CharonPDX - Monday, October 31, 2011 - link

    I am often in crowded areas where I theoretically have a strong 3G signal, but have no data throughput. Yet if I drop to EDGE (on my old iPhone,) I can get slow-but-usable data service.

    I also use it to save battery life.

    On the 4S, I can't do that any more. And *REALLY* aggravatingly, Apple advertises "2G battery life", yet you can't force it into 2G mode any more!
    Reply

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