PNG encoder/decoder for PHP

Is there any implementation of a PNG encoder/decoder written in PHP? 开发者_StackOverflow社区Something similar to this one: http://packages.python.org/pypng/png.html

I know there is GD and other ones, but as far as I know, you cannot have greater control over png chunks since they are png specific.

Thanks,

Nano.

Basically I will like to add certain types of chunks, like sPLT (which they are not that hard to be added manually). However, I cannot find a way to create the image data itself. I will like to create true-color images with 16 bits per channel, but the IDAT chunk is not as straightforward as other chunks.