Hi, during the last couple of months I've spent some spare time investigating the PNG format and the encoders generating it. During the investigation some facts popped up: * the JDK own encoder performance is horrible * the CLib one (provided by ImageIO native libs) does a lot better, but still leaves something to be desired and generally speaking builds larger PNGs
The JDK one is so slow because it rigged to provided the maximum possible compression, and it spends a lot of effort getting it, without giving any possibility to configure it. The thing is, that much effort normally just results in a size that is less than 10% smaller than more relaxed approaches, especially with the vector maps that GeoServer is normally producing. Given the above, and also considering that often people just do not install the ImageIO native extensions, and on some platforms (Win64, OSX) they are simply not available, I've setup to build a faster pure java encoder, concentrating most of my work to make sure we do the minimum amount of pixel scans and array copies before writing out the PNG file (something that apparently all existing encoders are rather bad at). The results are good, today I have two solutions which are both faster than the JDK one (by a lot) and normally faster than the CLib native encoder too. One is based on a minimal encoder that I wrote (called just NG for the moment), which is really bare bones, the other one is based on PNGJ, a open source, low level, pure java PNG encoder that is fully featured and that I've discovered a when the basics for the NG encoder were already laid down. I've exchanged quite a few mails with the PNGJ author and while at the beginning it was visibly slower, after some changes it came to be almost on par. The buffered-image.html file attached contains the results of a pure image encoding benchmark (the image is ready at the beginning of the banchmark) which I've built using Carrot Search Lab's JUnit-Benchmarks (http://labs.carrotsearch.com/junit-benchmarks.html). The benchmark encodes images using different types of colors and pixels representations, ranging from RGB(A) in either bytes or packed ints, grayscale images, and paletted ones. As you can see, either the NG or PNGJ can run circles around the JDK own writer (between 5 and 10 times times faster and they still have some advantage over the CLib one (30-40% faster) while building images that are, size wise, in between the CLib encoder and the JDK one. I've also made a benchmark based on sample vector (coming from osm-in-a-box) and raster maps of different sizes, attached as samples-benchmark.html, in this one I've spared the JDK encoder the embarassement and just compared clib, ng and pngj. As you can see the story is more or less the same, although on raster images pngj still needs some work to match my own bare bones encoder. All the code wrote so far is available here under the GPL license: https://github.com/aaime/png-experiments The next step would be to turn this into a WMS output format, directly, without the overhead of going trough the JAI ImageIO ImageWriter interface, so that's where the community module comes into the picture. Generally speaking, if at all possible, I'd like to drop my own encoder in favour of PNGJ to lower the maintenance overhead and better feature set, hopefully talking a bit more with the author will solve also the small raster encoding extra cost. Opinions and feedback welcomed (and of course, votes for the new community module) Cheers Andrea -- == Our support, Your Success! Visit http://opensdi.geo-solutions.it for more information. == Ing. Andrea Aime @geowolf Technical Lead GeoSolutions S.A.S. Via Poggio alle Viti 1187 55054 Massarosa (LU) Italy phone: +39 0584 962313 fax: +39 0584 1660272 mob: +39 339 8844549 http://www.geo-solutions.it http://twitter.com/geosolutions_it -------------------------------------------------------Title: Benchmark results for methods in class org.geoserver.png.BufferedImageEncodingBenchmark
Benchmark results for methods in class org.geoserver.png.BufferedImageEncodingBenchmark
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Benchmark results for methods in class org.geoserver.png.SamplesEncodingBenchmark
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