51455 2010-12-22 02:09:00 -0800 [chromium] Reduce canvas.toDataURL("image/png") run-time costs 300% 2010-12-23 00:00:47 -0800 1 1 1 Unclassified WebKit Canvas 528+ (Nightly build) PC Windows 7 RESOLVED FIXED P2 Normal --- 1 noel.gordon webkit-unassigned abarth commit-queue fishd mdelaney7 mikelawther oldest_to_newest 325424 0 noel.gordon 2010-12-22 02:09:00 -0800 Chrome win32 is 2 times slower than Mozilla 3.6.12 win32, and 3 times slower than Safari 5.0.3 win32 in my testing when calling canvas.toDataURL("image/png"). 325425 1 77198 noel.gordon 2010-12-22 02:15:03 -0800 Created attachment 77198 patch 325827 2 noel.gordon 2010-12-22 18:12:36 -0800 Extraction results for 800 x 600 px test image, this to determine the compression level used by chromium with the default libpng compressor. safari 5.0.3 win32 (baseline) x, extract image/png 167 ms length: 1171790 bytes chrome 10 win32 dev, for compression levels [1-9] 1, extract image/png 168 ms length: 1237066 bytes 2, extract image/png 179 ms length: 1222386 bytes 3, extract image/png 216 ms length: 1188118 bytes 4, extract image/png 264 ms length: 1136778 bytes 5, extract image/png 331 ms length: 1120050 bytes 6, extract image/png 510 ms length: 1098442 bytes ** default 7, extract image/png 623 ms length: 1091738 bytes 8, extract image/png 890 ms length: 1087218 bytes 9, extract image/png 929 ms length: 1086930 bytes Conclusion: chrome uses the default compression level 6, and is noticeably slower than Safari even though we both use libpng. For a compressed output size matching Safari (compression level 3), chrome is still ~50% slower than Safari. 325836 3 noel.gordon 2010-12-22 18:44:25 -0800 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. 325847 4 77294 noel.gordon 2010-12-22 18:56:42 -0800 Created attachment 77294 patch update changelog description 325884 5 77294 abarth 2010-12-22 21:07:37 -0800 Comment on attachment 77294 patch update changelog description Sounds like a win to me. 325915 6 noel.gordon 2010-12-22 23:44:35 -0800 Darin mentioned that this seems like something developers should be able to configure, and I concur. As a developer, I can control jpeg compression quality, but not png compression quality :( 325917 7 77294 commit-queue 2010-12-23 00:00:39 -0800 Comment on attachment 77294 patch update changelog description Clearing flags on attachment: 77294 Committed r74541: <http://trac.webkit.org/changeset/74541> 325919 8 commit-queue 2010-12-23 00:00:47 -0800 All reviewed patches have been landed. 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