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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  • doobydoo - Friday, December 2, 2011 - link

    You don't have to be concerned with something to care about getting an improved version.

    For example, I may be quite happy to work for a salary of £1,000,000 a year, but that doesn't mean I wouldn't care if my salary was doubled.
    Reply
  • Grandpa - Wednesday, November 9, 2011 - link

    Anyone heard of staticgate yet? How come nobody gives a review about the static issue on the iphone? Reply
  • mymomentummedia - Thursday, November 10, 2011 - link

    Here is a funny iphone 4s review... iphone 4s plus a 50.cal Barret sniper rifle. what do you get?

    http://www.youtube.com/watch?v=RsVEbRt6g94
    Reply
  • chillstatus - Monday, November 14, 2011 - link

    I made sure to switch my dataplan over to the "Unlimited Data Plan for iPhone 4S" and when I run the field test, it still says it's using wap.cingular. I live in Los Angeles, and am wondering how I can get it to use the faster network. Anyone else have this issue? Reply
  • rhch - Sunday, February 5, 2012 - link

    I just found out that my 4S wifi range is not as good as my old iPhone 4 or iPad 2.
    4S gets much earlier "no connection" with Safari, Appstore etc when i take distance to my hotspot.
    Can someone confirm this?
    Reply
  • AlexD - Monday, February 6, 2012 - link

    With this commend I ask for help to find a developer for an iPhone-App that enables to use the 4S for the catching of light below 380nm (UV) and above 780 nm (NIR). The purpose is to identify light emission of materials (inks, plastics) outside the visible range and to visualize it with the smartphone. Even a slight range (e.g. >320nm or <850nm would help me.
    I would also be very greatful if somebody could explain what range of wavelength the 4S camera sensor is catching, if there are filters which can be removed or exchanged or the like to enable the above function. Thanks in advance for your support.
    Reply
  • meace - Sunday, February 12, 2012 - link

    Is the POP memory attachment to the A4 permanent?
    As in... could that pop ddr sdram of 128 *2 be replaced with 256 *2 ?
    I'm guessing there's no way that it's coming apart without damage
    (maybe even in a clean room) but I'll ask.
    Reply
  • vitaprimo - Saturday, August 18, 2012 - link

    I don't think it's the phone's fault that much. I have two iPhone 4s (not 4Ss) on different carriers (Telcel and Iusacell) and the never lose signal, no matter how tightly I grip them and I don't use cases. Now, one of the carrier is relatively new in my state and out of the major cities I've had a few dropped calls but they always connect back. I use to have iPhone 4Ss and I noticed no difference; I lost a bag with the phones in it so I'm using my old 4s until the sixth comes out--hopefully in less than two months.

    This whole antenna issue seems to just be affecting carriers in the US--that being AT&T.
    Reply
  • phero - Friday, January 18, 2013 - link

    Thank you very much for this extensive review, especially the part about power consumption. It has given me all the information I needed for a well informed decision on which phone to buy. Reply

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