On Sun, 28 Dec 2025 17:36:51 GMT, Daniel Gredler <[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. > > Do you have a JMH test for the attached graph that can be used to replicate > locally? If you've not used JMH before, or haven't used it in the context of > OpenJDK, you can check existing performance tests in the `test/micro` > directory, or see this example (not part of OpenJDK, just something I've used > in the past to test things locally): > https://gist.github.com/gredler/e8ff9d52440cd103cd5b7766defff5b8 @gredler Thanks. I'm not familiar with JMH. I used your example (and a lot of googling) to set up a basic benchmark that is now attached to this ticket. For a 2500x2500 px image, the time on my Mac went from approx 25.296 to 22.132. Is there any interest in me: A. Creating a graph as the image dimensions change? B. Contrasting this implementation against ImageIO? I'm not sure what the long-term usage of this benchmark .java would be. If this PR is accepted: the slower "before" time will be not be relevant to anyone going forward. And the most important question (IMO): is there enough interest in this group to review/accept this proposal? (If not: I can stop spending time on it.) ## Before this PR Benchmark Mode Cnt Score Error Units PNGImageDecoder_8bit_uninterlaced.measurePNGImageDecoder avgt 15 25.296 ± 0.521 ms/op ## After this PR Benchmark Mode Cnt Score Error Units PNGImageDecoder_8bit_uninterlaced.measurePNGImageDecoder avgt 15 22.132 ± 0.378 ms/op ------------- PR Comment: https://git.openjdk.org/jdk/pull/29004#issuecomment-3695319015
