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A minimal PNG encoder for J2ME

(including a minimal ZLIB encoder)

I wrote this in a funny sort of mood when playing around with the limitations of MIDP 1.0. Although I didn't actually have any use for this myself, it has attracted more interest than anything else on my site, so I happily decided to address it as a separate topic here ;-)

A minimal PNG stream consists of a signature followed by a header chunk, a data chunk and a trailer chunk. Each chunk is verified by a CRC checksum. The data chunk contains a ZLIB block representing the actual pixel data. In the spirit of writing a minimal encoder, I used the most simple ZLIB block format containing only uncompressed deflate blocks.

Download: PNG.java

09/22/08 Fixed Adler checksum calculation and byte order for storing length of zlib deflate block. Thanks to Miloslav Růžička for noting this.
05/12/09 Added support for images > 64K by splitting the data into multiple uncompressed deflate blocks. In the process, split PNG and ZLIB functionality into separate classes.

Terms of Use: You may use the PNG encoder free of charge for any purpose you desire, as long as you do not claim credit for the original sources and agree not to hold me responsible for any damage arising out of its use. If you have a suitable location in GUI or documentation for giving credit, I'd appreciate a mention of

   PNG encoder (C) 2006-2009 by Christian Fröschlin, www.chrfr.de

but that's not mandatory. Of course, if you use my PNG encoder in your application, I'd also be happy to hear about it.

Limitations: The image data remains uncompressed, so the encoder may not be suitable for large images.

Extensions: Cody Konior has successfully combined my PNG encoder with JZLib for his Biorhythm application at mobilebio.sourceforge.net, so you might wish to check out his encoder class if you are looking for something with compression.

Related: Helmut Dersch has written a pure Java JPEG decoder.

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Copyright (C) 2006-2013 by Christian Fröschlin. Please note the legal disclaimer. If you experience problems with this page, contact webmaster@chrfr.de.