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by kragen
3932 days ago
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I see! That makes more sense. Thank you for explaining? A linearly-separated 2D 8×8 DFT should involve 6 butterflies per pixel, no? And I guess a 2D DWT with 8 coefficients results in 16 multiply-accumulates per pixel? Does it depend on the order of the DWT? |
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Not sure what you mean by the order of the DWT. Do you mean how deep you transform (how many levels of the transform you apply), or the number of taps on the filter?
It definitely depends on the number of taps on the filter.
IIRC, as for the depth DWT down to one scale coefficient is still O(N) (although there's another constant factor multiplied on beyond the number of filter coefficients). Even if you only do two levels, I believe you only cut the time in half, and you lose a lot of opportunity for compression if you do. I'm not sure what depth JPEG 2000 goes to, but it's probably more than three, so I think you can largely discount any perf gains there.