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

  • crankerchick - Tuesday, November 1, 2011 - link

    Nice in depth review. AnandTech is the best place to get quality reviews. Thanks! Reply
  • Death666Angel - Tuesday, November 1, 2011 - link

    I don't really see how a doubling of bandwidth (3GS->4->4s) is "more dramatic" than a tripling (3G->3GS). I am also not really impressed that smartphones now have the bandwidth of PCs from 7 years ago. After all, they have a great copy sheet. Reply
  • Soldier1969 - Tuesday, November 1, 2011 - link

    If you already have a I4 this is NOT worth the upgrade! Waste of money. Much better options out there for a upgrade path the 4S isnt it...and Ive had the Iphone since release. This was a huge disappontment and failure for Apple. The only reason it sold as much as it did was all those people that still had the 3GS from 2 or 3 years ago or new customers. If you had a 4 already your just a "moop" if you upgraded to one of these! Reply
  • PeteH - Tuesday, November 1, 2011 - link

    Depends what you are looking for in an upgrade. That graphics performance is pretty incredible. If you want to develop games pushing the boundaries of what is possible graphically on a mobile device the 4S makes a lot of sense. Reply
  • Lucian Armasu - Wednesday, November 2, 2011 - link

    The graphics performance "in a benchmark". As you could see in the review, it only gets about double the FPS in real games, because it's bound by memory bandwidth.

    I doubt the games can run any faster or look any better than other current GPU's in mobiles.
  • thunng8 - Wednesday, November 2, 2011 - link

    wow, what an absurd statement. Several games that were optimised for the new graphics increased their details level greatly and also added FSAA. You should have a look before passing judgement. Reply
  • *kjm - Tuesday, November 1, 2011 - link

    Unless your like me and on Sprint comming from a Samsung M800 that is going on 4yrs old. I would think "most" people that can upgrade don't to stay off contract as long as the phone is working for them. Reply
  • doobydoo - Wednesday, November 2, 2011 - link

    What would be a 'better option' right now, to upgrade an iPhone 4 to? Reply
  • Lucian Armasu - Wednesday, November 2, 2011 - link

    The differences are not that big hardware wise at this point, so it will be more of a decision based on software. If you like iOS 5 you get an iPhone 4S, if you like Android 4.0, you get a Galaxy Nexus. If you like a different phone design, you get a Droid RAZR.

    I don't think the upgrade from iPhone 4 to iPhone 4S would be worth it anyway. Maybe from iPhone 3GS, for those who want to stay in the Apple ecosystem.
  • weiran - Wednesday, November 2, 2011 - link

    > If you like a different phone design, you get a Droid RAZR.

    Which is ugly as sin, and isn't really an "upgrade" from an iPhone 4.

    IMO from a design POV the most interesting iPhone competitor right now is the unreleased Nokia Lumia 800, for hardware and software.

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