Error on Recompiling with gfx.py

[Lucern7]

I found your handy source code and followed the instructions but when compiliing I get this error involving gfx.py here's what the terminal tells me...

$ make
Traceback (most recent call last):
File "extras/pokemontools/gfx.py", line 1442, in
main()
File "extras/pokemontools/gfx.py", line 1438, in main
method(args.filenames)
File "extras/pokemontools/gfx.py", line 1366, in convert_to_2bpp
export_png_to_2bpp(filename)
File "extras/pokemontools/gfx.py", line 994, in export_png_to_2bpp
image, arguments = png_to_2bpp(filein, *arguments)
File "extras/pokemontools/gfx.py", line 1073, in png_to_2bpp
width, height, rgba, info = png.Reader(filein).asRGBA8()
AttributeError: 'module' object has no attribute 'Reader'
Makefile:79: recipe for target 'red/main.o' failed
make: ** [red/main.o] Error 1

I'm not sure what the issue is, normally I'm decent at deciphering code but this one has me stumped.