Writes the bitmap as a PNG image: 8-bit RGB when every pixel is opaque, otherwise 8-bit RGBA with alpha un-premultiplied.
public void SavePng(Stream stream)
The stream to write to.
PNG (ISO/IEC 15948, W3C Portable Network Graphics Specification, third edition): IHDR, one zlib-compressed IDAT with an
adaptive filter per row, IEND. A colour channel c of alpha a is written as round(c × 255 / a), which
premultiplying again with rounding returns exactly.