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

  • thunng8 - Thursday, November 3, 2011 - link

    You do realize that the top 3 results are all vsync limited? They are all close to 60fps. That makes it not a great test to show the full potential of the gpu. Reply
  • ReverendDC - Friday, November 4, 2011 - link

    I was wondering why there were no WPs in your comparison. They have comparable screens, functionality, and features.

    This is NOT to start a flame war. I am curious about how some of the newer WPs especially line up (Titan, Lumina 800, Focus S, etc).

  • mymomentummedia - Sunday, November 6, 2011 - link

    Here is a 360 degreee review of the iPhone 4s with a beautiful girl in a swimsuit... no complaints here.
  • yeatzeck - Sunday, November 6, 2011 - link

    According to the Chipworks ( in iPhone 4S is Sony's camera (they even X-ray it).
    You probably have to update the review.
  • mosmov - Monday, November 7, 2011 - link

    You've run the Taiji for many devices so far.
    I'd like to see the number also for 4S to align the result with other devices in my memory.
  • tipoo - Monday, January 2, 2012 - link

    Taiji is for Android... Reply
  • Conficio - Monday, November 7, 2011 - link

    Text dictation is a neat feature for sure, but to be honest I’m still not likely to rely on it for sending or replying to messages. It’s convenient while driving but the accuracy isn’t high enough to trust it with sending messages to important contacts.

    Here is the viral tip for Apple (or its competitors). Make it an option to deliver the text as well as the ability for the recipient to actually listen to the voice command recorded (sans the edit commands, etc.) That will become fast the fastest way to leave voice messages, because you don't have to wait for the phone to dial, time out and get through the voice mail instructions.
  • HelloChris - Monday, November 7, 2011 - link

    Long time reader, but something in this review made me register a username so I could add to the comments...

    Anand's webpage-refreshing battery life test saw the iPhone 4S achieve around 10 and 11 hours, for 3G and WiFi, respectively. However, MANY new 4S owners (including myself) have been getting battery life which is roughly half of that. I just finished reading this whole review, and I have to wonder if the test unit sent to Anandtech might have been hand-picked by Apple? 10/11 hours is just so much more than everyone else seems to be getting. I've averaged 6.5 hours of total usage, and this includes several hours of use where I'm using absolutely no 3G/WiFi data, and minimal processing power (example: viewing a PDF, viewing pictures, reading items on my Google Reader feed)...

    If you look on the major apple forums there are multiple threads where there are many users experiencing the same conditions.

    Also, I'm aware of the battery issue with iOS 5 (which Apple acknowledged last week and has a beta update out already for) which implies that this is indeed a software, not a hardware issue.

    Perhaps I'm missing something, but if it's the case that AnandTech received a well-performing test unit, that would explain their extraordinary battery life.
  • doobydoo - Friday, December 2, 2011 - link

    I think you answer your own question.

    It sounds like your phone is affected by the battery life issue for which a software patch has been released, wheras Anand's probably wasn't.

    The vast majority of iPhone 4S owners didn't experience any issues with battery life.
  • medi01 - Tuesday, November 8, 2011 - link

    To care about "improved vibration" I have first to be somehow concerned with current "unimproved" vibration. Which I don't. And I don't know any person that is. Reply

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