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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  • dacramer - Tuesday, November 1, 2011 - link

    The browser benchmarks show the 4s as fastest, but this benchmark is FLAWED as a measurement of CPU performance.

    The benchmark compares Safari to the Android stock browser. The stock Android browser does not support 2 cores, only 1. So all Android dual cores phones would be nearly twice as fast with another browser such as Opera.

    I'm surprised Anand did not include this discussion in the review. He seams fixated on the idea that stock to stock browser is a valuable comparison when it totally misleads readers on CPU performance.
    Reply
  • Lucian Armasu - Wednesday, November 2, 2011 - link

    In case you missed it, the Droid RAZR scored 10% faster than iPhone 4S in the SunSpider test.

    But yes, this is still mostly a software issue, and I expect the Android 4.0 browser to be even faster on the same chip.
    Reply
  • thunng8 - Wednesday, November 2, 2011 - link

    FYI, Google says the Galaxy Nexus scores 1983ms in Sunspider running ICS Reply
  • doobydoo - Wednesday, November 2, 2011 - link

    "Where did it show faster CPU?"

    Where did it in my comment?
    Reply
  • Breit - Thursday, November 3, 2011 - link

    I just run SunSpider 0.9.1 on my Galaxy S2, international model (everything stock, with Android 2.3.5) and it came in at 1626.5ms with Opera Mobile browser and 3354.8ms with the stock Android browser. So saying the CPU on the Galaxy S2 is weaker than the CPU on the 4S is just not right (and that by a big margin!).
    At least make comparisons with the best software there is and not just 'some' browser you eventually found on your phone...
    I'll bet there is someone programming his own browser just for the kicks or as an exercise for his programming skills and that browser scores over 9000ms in SunSpider. Does that mean the CPU in that phone is slow? ;)
    Reply
  • doobydoo - Friday, December 2, 2011 - link

    You could achieve the same results on the iPhone too..

    The comparison is (rightly) comparing stock browser to stock browser, and the iPhone 4S is faster. It would be even faster again using say, Opera.

    As for some guy posting 9000ms - you can filter the results to 'best' times so this is a non issue.
    Reply
  • Tetracycloide - Tuesday, November 1, 2011 - link

    Isn't there more to displays than just white level in nits, black level in nits (on a chart were I can't seem to find the Galaxy S II or the Infuse), and contrast (again, don't see the Samsung Galaxy S II or the Infuse on the contrast chart either)? Don't get me wrong, I don't agree in the slightest with the summary "this is apple cheerleading" but honestly the display comparisons are pretty lacking IMO. Where are the rest of them? There's more to a screen than just nits. Reply
  • medi01 - Thursday, November 3, 2011 - link

    Last time iphone disappeared from comparison photo, from the one where it would pale in comparison, when asked, author "explained' that he simply "forgot" it in the pocket. (!!!). Now they didn't even bother. Round of but kissing on "retina" hype and phones disappearing from charts.

    Find contrast of Galaxy phones on the charts pretty please...
    Reply
  • steven75 - Friday, November 11, 2011 - link

    Could you be any more of an Fandroid? Seriously. Reply
  • Stuka87 - Tuesday, November 1, 2011 - link

    Wait what?

    Almost every single page has a comparison to Android phones. Several of them have graphs showing the differences!

    And your comment on the displays may be your opinion, but actual measurements show otherwise. but hey, if you like your over saturated display with a much lower pixel density, thats your decision.
    Reply

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