This clause defines basic data representations used in reference and PNG images, as well as the expected representation of the image data.
Values are unsigned unless otherwise noted.
Values explicitly noted as signed are represented in two's complement notation. A PNG datastream consists of a PNG signature followed by a sequence of chunks . This clause defines the signature and the basic properties of chunks. This signature indicates that the remainder of the datastream contains a single PNG image, consisting of a series of chunks beginning with an IHDR chunk and ending with an IEND chunk. Length A four-byte unsigned integer giving the number of bytes in the chunk's data field.