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


View All Comments

  • Pata - Tuesday, November 1, 2011 - link

    Will these factors (bluetooth and gps) be incorporated in future tests? I now keep bluetooth and the gps on for Siri and geofenced reminders. I'm guessing that Android phone users might be soon be using bluetooth more often as well, given all the bluetooth watch accessories that will soon be available for their platform. With bluetooth and gps left on, with find my friends, reminders all running in the background, my iPhone usually doesn't last anywhere up to 9 hrs of usage. Reply
  • DukeN - Tuesday, November 1, 2011 - link

    Thanks Anand for reviewing every single Apple, iOS, Android/Droid major and minor update since the summer. How about we perhaps devote 2 frickin pages to cover/preview/benchmark some of the newest Blackberry devices?

    Heck you even covered turds like the HP Veer, and Windows Phone devices.

    Perhaps we can devote a couple of pages to the smartphones that have a quarter of the market?

  • jamyryals - Tuesday, November 1, 2011 - link

    Even as a [forced] Blackberry user, I'd rather they didn't spend their time reviewing Blackberry devices.

    Also, it is "biased" in that case.
  • SicMX - Tuesday, November 1, 2011 - link

    Fantastic review, keep up the good work!

    PS. Especially appreciated the in-depth review regarding the camera + image quality.
  • Matt Campbell - Tuesday, November 1, 2011 - link

    Nice article Brian, Anand. One clarification for Page 8, Siri can't read emails - only incoming (new) text messages. She'll tell you this herself if you ask her to read your emails :)

    And one comment, the addition of Bluetooth 4.0 is a big leap forward in my opinion. The Bluetooth stack in every other iPhone revision was missing the Serial Port Profile stack, which severely limited hardware developers. Since the 4S is "Bluetooth Smart Ready", it should support all kinds of fun new sensors and gadgets without the need for additional hardware.
  • _tangent - Tuesday, November 1, 2011 - link

    Great in depth review! Anandtech is one of the only places you can find this sort of analysis, and for the technically minded consumer, it's an invaluable resource. Kudos!

    I'm a bit confused by the GPU arms race in the mobile space. Aren't we reaching a point where the screen is small enough and far enough away from your face that the law of diminishing returns applies? Unless the ultimate objective is to have us all connect our phones to tvs or other displays for gaming on a larger scale.

    I'm not sure where i stand on mobile gaming these days. I have a relatively capable android handset, but find myself not even playing the 3D games already available. Not because they aren't good or pretty enough, just because intensive 3d gaming slams my battery, is less well suited to the odd 5 minute opportunity i get to game on the go, and the lack of physical controls for more "conventional" games is often frustrating. In any case, having lived with the handset for 6 months or so, i'm not clamoring for better 3D performance. Maybe plenty of people are though.

    I'm not personally a fan of Apple products. Not because they don't offer a great UX and aren't well polished in their own right, but because the cost apparently associated with that is too high. As a software developer by trade I find their draconian, fascist approach to the appstore and development in general somewhat distasteful. I don't equate choice and flexibility with complexity. That said, i don't mind Apple in a world where they have competitors offering an alternative philosophy This drives everyone to innovate which is great for us as consumers.

    Hopefully ICS will bring Android up to par with iOS from a UX point of view, whilst retaining the flexibility and customization that much of it's user base has come to appreciate. I look forward to a similarly comprehensive look at the Galaxy Nexus and other ICS phones as they're released!
  • Shinobi123 - Tuesday, November 1, 2011 - link

    Why is the New Razr missing from most of the graphs? It was in the first few, basically the only reason I kept reading this article.. But it wasn't included in any. :( Reply
  • tipoo - Tuesday, November 1, 2011 - link

    They probably aren't done testing it. Reply
  • rimshaker - Tuesday, November 1, 2011 - link

    As usual, the very best in depth product review available. As a EE, no review is ever thoroughly complete until I read it here on Anandtech. Wonderful!

    My only question is how to display the numerical wifi RSSI without using 3rd party apps? I tried it in field test mode but the wifi icon never changes like the cell signal does.
  • dubthedankest - Tuesday, November 1, 2011 - link

    I second this question as well as the one prior on how to enable the numerical RSSI for WiFi - that would be very helpful.

    Great review!

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