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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  • Lucian Armasu - Wednesday, November 2, 2011 - link

    Anand, you said the GLbenchmark is the only good cross-platform graphics benchmark. Was GLBenchmark made originally for iOS? Don't you think that it could be biased (possibly unintentionally) towards shader performance in its scores, which would make it favor the PowerVR GPU's more?

    At the end of the day, these are all just syntethic benchmarks, and sometimes they could be way off from real world performance tests. So what if GLBenchmark doesn't give a too big score for stuff that the other chips are good at, like physics, geometry, whatever, and it gives higher score for shader stuff?

    Another question, don't you think shader performance is starting to limit what the games can show about now? Will it really help games that much if they received 20x shader performance in the next 2 years?
    Reply
  • thunng8 - Wednesday, November 2, 2011 - link

    Glbenchmark was originally release for Linux, Symbian and Windows Mobile. Reply
  • thunng8 - Wednesday, November 2, 2011 - link

    Also you do realize that Glbenchmark consists of many tests including some primitive tests like fill rate and Geometry?

    By other Gpu, do you mean the Mali-400 or GeForce ulp? The standout result I saw was how weak the Mali was at geometry being 4x slower while fill rate was less than 2x slower than the 543mp2
    Reply
  • lemmo - Wednesday, November 2, 2011 - link

    Thanks for the review, but did I miss analysis on audio quality... for music, not voice quality?

    You've started this with the Galaxy S2, really useful, and I believe you're developing your testing methodology. But any indication how the iPhone audio quality compares to S2, Prime and others?
    Reply
  • cacca - Wednesday, November 2, 2011 - link

    if nobody has photo-shopped the images at page 3 i not quite strenge that you have a better throughput.

    iPhone 4 test done at PM 4.24, a normal afternoon, with quite a lot of traffic

    iPhone 4s test done at AM 3.34, a quite early bird, no problems or fight for resources with other phones

    To you is normal to test at so different times? An for you there is no difference between a late afternoon and 3.34 in the morning?

    bah
    Reply
  • koinkoin - Wednesday, November 2, 2011 - link

    I was wondering what the battery time is when you call with a headset. I do almost all my call with a headset to keep my hand free (on the wheel or keyboard). How much does this affect the battery time.
    Also I use a Blackberry and it always check for new email, I sometime read the mail while on the phone, when you do the talk time test is there a connection for email open?
    Reply
  • koinkoin - Wednesday, November 2, 2011 - link

    I was wondering what the battery time is when you call with a headset. I do almost all my call with a headset to keep my hand free (on the wheel or keyboard). How much does this affect the battery time.
    Also I use a Blackberry and it always check for new email, I sometime read the mail while on the phone, when you do the talk time test is there a connection for email open?
    Reply
  • Griswold - Wednesday, November 2, 2011 - link

    I dont think the results the new camera deliver are superior to the one in the iphone4. Judging by the vast number of shots Engadget compared between these two phones and a couple other premium phones, the iphone4s shows alot more noise than the older model, even in broad daylight. Its probably the increased pixel count, which cant be countered by the other improvements.

    Its not bad, but its also not better than the old camera. The old saying remains true: more pixels doesnt equal better pictures.
    Reply
  • jwwpua - Wednesday, November 2, 2011 - link

    In the section WIFI, GPS, AUDIO, SPEAKERPHONE, I don't see anything about the speakerphone. Is it louder? Any tests done? Clarity?

    Thanks, great review!
    Reply
  • freezer - Thursday, November 3, 2011 - link

    I think you should have the GPU benchmark using phone's native resolution. That would give more accurate results in real world gaming situation than running all phones using same resolution.

    The iPhone 4S 3.5" screen has much more pixels than Galaxy S2 4.3" screen which gives latter advantage in 3D speed. That is because the GPU has to draw every pixel in every frame. There's no way around it.

    In fact running GL Benchmark 2.1 Pro High in native resolution gives very different results as Galaxy S2 comes at top:

    http://glbenchmark.com/result.jsp?benchmark=glpro2...
    Reply

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