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  1. #1
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    Jul 2007
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    Performance of JPEG decoding

    Dear experts,

    We use a N82 device to acquire 2048x1536 pixel images (3MP) and convert the resulting JPEG image to bitmap with CImageDecoder.

    Unfortunately, this takes usually about 2 seconds and even if reducing the JPEG quality accelerates the encoding process significantly, the decoding process is not accelerated as expected.

    Can anybody provide advice how to improve the speed for image acquisition? We need a 3MP colour bitmap and see no other way, since the devices is unable to directly provide anything but JPEG images.

    Sincerely,
    TW

  2. #2
    Nokia Developer Moderator
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    Re: Performance of JPEG decoding

    As far as I understand, processing requirement of JPEG decoding depends much more on the size than on the quality. Do you really make use of the full uncompressed image on the device? Because it is possible to decode the image in smaller size.

  3. #3
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    Re: Performance of JPEG decoding

    This is a genuinely tough problem. The solution suggested by wizard_hu_ is very sensible. If that isn't possible for your use case then you could possibly license the technology from Scalado AB to manipulate JPEGs without decoding them fully.

    The JPEG decoder is already fairly well optimized, I don't think you'll get it much faster without more powerful hardware.

    Sorcery

  4. #4
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    Re: Performance of JPEG decoding

    Thank you both for your contributions! We will have a look at the Scalado AB technology. Unfortunately, we apply advanced computer vision algorithms and really need to read every single pixel of the image.

    There is no way to access the camera chip's memory?

    Sincerely,
    TW

  5. #5
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    Re: Performance of JPEG decoding

    I'd guess your CV algorithms running on a full 3MPix image are likely to be much more of a problem than the JPEG decode if you do anything interesting. Seriously consider smaller images.

    If you restrict yourself to a specific phone then you might be able to partner an API to get lower-level access. In many cases the JPEG encode takes place on a separate chip that sits between the camera sensor and the application processor - there's no way to access it. It might be possible in some cases to get the raw data from the sensor, but then the transfer from the camera itself will take a long time since there's a lot of data and the camera interface on a lot of the application processors is pretty slow.

    An alternative solution is just to wait for more powerful hardware!

    Sorcery

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