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Thread: Looking for parallel algorithm for MQ coder

  1. #1
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    Looking for parallel algorithm for MQ coder

    Hello,
    I am implementing a jpeg 2000 encoder in OpenCL.
    So far, the T1 phase up to but not including MQ takes 10 ms for a 2048x1024 RGB image,
    on a 3 year old HD 7700 card. MQ encoding takes 140 ms !! Because
    it is very serial, and has many branches.

    So, I am looking for a way more suitable to massively parallel device.

    Any ideas would be most welcome.

    Thanks,
    Aaron

  2. #2
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    Well, as everyone but me no doubt knows, this algorithm cannot be parallelized

    But, it occurred to me that it is possible to parallelize across colour channels, for example. So, for each code block,
    three threads can simultaneously encode a code block from one of the three colour channels.

    Also, it can get better: multiple tiles and/or multiple frames can be encoded concurrently. My use case
    is digital cinema packaging, so I can group N frames together and encode them together. This introduces some latency,
    but it is quite manageable: 25 frames == 1 second latency.

    This assumes that I can store the context information for all of these channels/tiles/frames in memory at one time.
    And it turns out that I can indeed do this, because of a trick I am using in processing the bit planes.

    For single image encoding, unfortunately this speedup is limited. The solution here would be to get a more powerful card,
    or multiple cards.

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