Fastest PNG decoder for .NET

Question

Our web server needs to process many compositions of large images together before sending the results to web clients. This process is performance critical because the server can

Answer 1

I've written a pure C# PNG coder/decoder ( PngCs ) , you might want to give it a look. But I higly doubt it will have better speed permance [*], it's not highly optimized, it rather tries to minimize the memory usage for dealing with huge images (it encodes/decodes sequentially, line by line). But perhaps it serves you as boilerplate to plug in some better compression/decompression implementantion. As I see it, the speed bottleneck is zlib (inflater/deflater), which (contrarily to Java) is not implemented natively in C# -I used a SharpZipLib library, with pure C# managed code; this cannnot be very efficient.

I'm a little surprised, however, that in your tests decoding was so much slower than encoding. That seems strange to me, because, in most compression algorithms (perhaps in all; and surely in zlib) encoding is much more computer intensive than decoding. Are you sure about that? (For example, this speedtest which read and writes 5000x5000 RGB8 images (not very compressible, about 20MB on disk) gives me about 4.5 secs for writing and 1.5 secs for reading). Perhaps there are other factor apart from pure PNG decoding?

[*] Update: new versions (since 1.1.14) that have several optimizations; if you can use .Net 4.5, specially, it should provide better decoding speed.