[Webkit-unassigned] [Bug 51455] [chromium] Reduce canvas.toDataURL("image/png") run-time costs 300% (compression strategy)

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=51455





--- Comment #3 from noel gordon <noel.gordon at gmail.com>  2010-12-22 18:44:25 PST ---
The alternative compression methods offered by libpng, namely, Z_RLE, Z_FILTERED,
and Z_HUFFMAN_ONLY, should then be considered.  Z_FILTERED is slower, and not as
compressive as Z_HUFFMAN_ONLY, Z_RLE.

Z_HUFFMAN_ONLY seems a good choice compared to Z_RLE - that latter runs about 2-10%
slower (see http://optipng.sourceforge.net/pngtech/z_rle) for similar compressed
output data size (http://optipng.sourceforge.net/pngtech/z_rle.html).

Does the libpng compression level alter the results when using Z_HUFFMAN_ONLY?  It
should not, but I varied the compression level from Z_BEST_SPEED (1) through to
maximal compression (9) to test: 

 huffman encoding (Z_HUFFMAN_ONLY) with compression levels [1-9] 

   1, extract image/png 156 ms length: 1204834 bytes 
   2, extract image/png 156 ms length: 1204834 bytes 
   3, extract image/png 156 ms length: 1204834 bytes
   4, extract image/png 164 ms length: 1204834 bytes
   5, extract image/png 168 ms length: 1204834 bytes
   6, extract image/png 166 ms length: 1204834 bytes
   7, extract image/png 166 ms length: 1204834 bytes
   8, extract image/png 167 ms length: 1204834 bytes
   9, extract image/png 166 ms length: 1204834 bytes

There was a consistent 10 ms increase in run-time cost for compression levels > 3.
Z_BEST_SPEED seems like a good choice.

-- 
Configure bugmail: https://bugs.webkit.org/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are the assignee for the bug.