To read/write data from a png image
description of constants
High storage density (4 bits per 8 bits)
Low storage density (1 bit per 8 bits)
Maximum storage density (8 bits per 8 bits)
Medium storage density (2 bits per 8 bits)
Possible values for density
names associated with above densities
quality names associated with above densities
Contains the functions to read/write to hidden data in png files.