On Mon, 29 Dec 2025 02:59:04 GMT, Jeremy Wood <[email protected]> wrote:
>> When decoding an uninterlaced 8-bit PNG image, the PNGImageDecoder is >> basically copying one byte at a time. >> >> This PR uses System.arraycopy instead, and it shows approx a 10% improvement. >> >> This graph shows the time it takes different decoders to convert a byte >> array into a BufferedImage as the size of the PNG image increases: >> >> <img width="596" height="366" alt="Screenshot 2025-12-27 at 9 14 19 PM" >> src="https://github.com/user-attachments/assets/73583cb2-eda0-47a8-b818-735a1835f1e8"; >> /> >> >> (This originally came to my attention when looking at an image in Java 1.8. >> There the ImageConsumer model took approx 400% longer than ImageIO. I was >> happy to see in recent JDKs that gap narrowed significantly, but there was >> still a noticeable 10% discrepancy.) >> >> I haven't tried submitting a performance enhancement PR before; I'm not sure >> if this issue meets this group's threshold for being worth addressing. And >> if it does: I'm not sure how to structure a unit test for it. > > Jeremy Wood has updated the pull request incrementally with one additional > commit since the last revision: > > 8374377: Adding a JMH test for PNGImageDecoder > > This corroborates previous (more informal) tests that show approx a 10% > improvement. > > Without this PR I observed this result on my Mac 26.2 laptop: > > ``` > Benchmark Mode Cnt Score > Error Units > PNGImageDecoder_8bit_uninterlaced.measurePNGImageDecoder avgt 15 25.296 > ± 0.521 ms/op > ``` > > With this PR I observed this result: > > ``` > Benchmark Mode Cnt Score > Error Units > PNGImageDecoder_8bit_uninterlaced.measurePNGImageDecoder avgt 15 22.132 > ± 0.378 ms/op > ``` With the patch, the code `case 8: bPixels[col+rowOffset] = rowByteBuffer[spos++];` at old line 415/new line 427 is now dead. Should we replace that site with an assertion, or just move the arraycopy code to there instead? ------------- PR Comment: https://git.openjdk.org/jdk/pull/29004#issuecomment-3704286867
