File png-define-window-size-20010413.txt It is proposed to add a definition of "LZ77 window size" where it first appears in PNG-1.2 section 5 and ISO-PNG Clause 10.1 as indicated: For PNG compression method 0, the zlib compression method/flags code must specify method code 8 ("deflate" compression) and an LZ77 window size + (which is an upper bound on the distances + appearing in the deflate stream) of not more than 32768 bytes.