Managed PNG Optimization Library Available? [closed]

Answer 1

Just in case you decide to write your own C# code: I've writen an open source pure Java PNG coder/decoder, PNGJ, you might find it useful; it should not be difficult to port to C#. It's just a coder, not an optimizer, but it supports all writing options/strategies (including different filters for each row) so you could easily plug your heuristics to it.

Updated: I've coded a C# PNG coder/encoder PngCs, ported from Java (PngJ), it's open source and, since Dec-2012 it supports all PNG variants (except that it does not write interlaced PNG, only reads them)

Answer 2

According to this answer there are several .net libraries that can be used to optimize the png size

The tools I use for png optimization are:

1. Convert to png8: If there are few colors (say, screenshots) then I use [pngnq][2] or Gimp's Indexed color mode to quantize down to 256 colors. Png8 can be smaller than png24 or png32. For details see [PNG8 – The Clear Winner][3].
2. Optipng, a fast general png optimizer. [C# PNG Optimization Tutorial][9] has details on how to run optipng from C#.
3. Finally [pngout][4] is slow but often (80-90% of the time) manages to squeeze the png down further than optipng. Run optipng first though, as optipng will automatically do other optimizations that pngout does not attempt.

Answer 3

After a fairly decent Google search and spotting one or two of these questions on StackOverflow recently, I don't believe there is a C# library available.

However, OptiPNG is open source C code, so porting to C# is a possibility. Alternatively, pull the C code out into a separate library outside of an exe and P/Invoke into it.

There appear to be other open source libraries around, not necessarily specifically for optimization:

http://www.libpng.org/pub/png/pngcode.html

Apologies for the anti-climax, I've been after one of these too and I've come to the conclusion the current answer is one doesn't exist. I eagerly wait to be corrected.

Answer 4

I've just found this one: nQuant. From the project page:

nQuant is a .net color quantizer that produces high quality 256 color 8 bit PNG images. nQuant often reduces the size of a 32 bit image to a size 3 times smaller than its original with quality surpassing what the standard C command line utilities produce.

I've tested it out with some sample PNGs and it really does produce a good 8-bit output, smaller than .NET's own 8-bit encoder and with no visible dithering, even for antialiased images. I miss one thing, however: the processing can be a bit slow, but the library unfortunately doesn't have a parallelized variant of the optimization code. I'm working on a solution for this.

UPDATE (Jan 21, 2013), I've refactored the code, it runs 10 times faster now, even without the parallel threads. The fork is here: http://nquant.codeplex.com/SourceControl/network/forks/breki74/nQuantFaster

UPDATE (Feb 24, 2013), my fork was merged to the trunk. Enjoy.