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Thread: ECT, an file optimizer with fast zopfli-like deflate compression

  1. #391
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    Quote Originally Posted by fhanau View Post
    The images, or at least the first few, are not fully opaque. 0.3% of the pixels of the first image are slightly transparent, which means the alpha channel can't be stripped losslessly. The first few images I tested are similar.
    Thank you. Zooming in i can se ther is a slight 1 pixel border where here is some slight transparancy.
    my compare tool is broken then when it comes to alpha

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    Quote Originally Posted by fhanau View Post
    Using an "ultra" value enables aggressive costmodel optimizations in ECT. If ultra is 1, ECT does 1 or more iterations where the costmodel assumes that the actual huffman bit lengths are the rounded theoretical, frequency-based values (usually no rounding takes place). Ultra=2 (or ultra2) does another iteration after all normal/ultra iterations with the ultra approach and also tries to use matches with a longer distance at the same length if this makes sense according to the costmodel. ultra=3 does ultra2 iterations until this does not yield any more saved bits. (Don't worry if you don't fully understand this, it is a really complex topic.)
    I've noticed that ultra2 is quite intensive and ultra3 can literally take months to finish, but doesn't seem to give much if any gain compared to just adding more iterations (at least on the many files I've tested). Is there a better way this functionality can be optimized?

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    Quote Originally Posted by MegaByte View Post
    I've noticed that ultra2 is quite intensive and ultra3 can literally take months to finish, but doesn't seem to give much if any gain compared to just adding more iterations (at least on the many files I've tested). Is there a better way this functionality can be optimized?
    If you use ECT for months on one file, you're just wasting CPU time. The ultra2 and ultra3 settings are very inefficient, especially on files with high redundancy. I have added a change that should lead to large speedups for ultra2/3 to the matchfinder-exp branch, but I haven't yet tested it and it needs to be cleaned up. Further improvements are possible by using a more efficient match finder (the main match finder can't be used for ultra2/3 since it needs to find some matches that the main mode does not bother with). Unfortunately, I won't have time to implement new features for ECT in the foreseeable future.

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    MegaByte (14th May 2019)

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    Quote Originally Posted by shailender_jain View Post
    That tool is lossy, while ECT is only designed for lossless compression for now.

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    nikkho (10th April 2019)

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    Quote Originally Posted by fhanau View Post
    I have added a change that should lead to large speedups for ultra2/3 to the matchfinder-exp branch, but I haven't yet tested it and it needs to be cleaned up.
    This branch does help tremendously, but sometimes hits assertions (which corrupt the file if removed).

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