PNG Chunks

[inna]

I'm writing a chunks collection program in png, please tell me how chunk idata is built? And if the chunk compression is used, what is the Python3 module available for compression?

[zymir]

You can look at the source of the library. https://github.com/jcrocholl/pypng/blob/master/lib/png.py where the reading/recording at PNG on a pure python has been completed. There's a universal method. Reader.read_chank()which reads the chunk and returns its type and data and method Reader.read() where all the sausage algorithms and the paintings implemented.

The key moment of data dispensation is here:

scanlines = array('B', zlib.decompress(''.join(compressed)))
if interlaced:
    pixels = self.deinterlace(scanlines)
else:
    pixels = self.read_flat(scanlines)

(in variables) compressed raw data from all chancs IDAT)

It is not difficult to figure out from the example that the data-packing module is called zlib.