This document describes two variants of a special-purpose chunk type that has been proposed for use in various PNG (Portable Network Graphics) and related multi-image applications. It has not yet been approved for registration by the PNG developers, and therefore is experimental and its format is subject to change. The proposed chunk is (with an unregistered name or names that can be used in test implementations shown in parentheses): eXIf (exIf, uxIf, zxIf). PNG uxIf (raw EXIF) proposal ============================ It is proposed to add the following section to the document "Extensions to the PNG 1.2 Specification, Version 1.2.0" 3.7. eXIf EXIF profile The four-byte chunk type field contains the decimal values 101 88 73 102 (ASCII "e X I f") When present, the eXIf chunk contains contains EXIF metadata that is compatible with specifications issued by CIPA, "Exchangeable image file format for digital still cameras" [CIPA DC-008-2016] or its successors. See https://www.media.mit.edu/pia/Research/deepview/exif.html The eXIf chunk contains an EXIF profile in a raw format: Data: length bytes where "length" is determined by the chunk "length" field, containing a raw EXIF profile. At most one eXIF chunk shall occur in a PNG datastream. There are no ordering constraints upon the position of the eXIf beyond those imposed by the PNG specification, i.e., if present, the eXIf chunk may appear anywhere between the IHDR and IEND chunks except between IDAT chunks. PNG zxIf proposal ============================ It is proposed to add the following section to the document "Extensions to the PNG 1.2 Specification, Version 1.2.0" 3.7. eXIf EXIF profile The four-byte chunk type field contains the decimal values 101 88 73 102 (ASCII "e X I f") When present, the eXIf chunk contains contains EXIF metadata that is compatible with specifications issued by CIPA, "Exchangeable image file format for digital still cameras" [CIPA DC-008-2016] or its successors. See https://www.media.mit.edu/pia/Research/deepview/exif.html The eXIf chunk contains an optional "mode" byte followed by an EXIF profile in a raw format or in a zlib-encoded compressed format: Mode: 1 byte 0: the remaining length-1 bytes of data make up a zlib-encoded EXIF profile written in accordance with chapter 5, "Deflate/Inflate Compression" of the PNG specification version 1.2 (which is Clause 10.1, "Compression method 0" of the ISO PNG specification). 69: (ASCII "E") the remaining length-1 bytes of data, combined with the byte "E", make up a raw uncompressed EXIF profile Other values of Mode are reserved for other compression methods which might be defined in a future version of this specification. Data: the remaining length-1 bytes where "length" is determined by the chunk "length" field At most one eXIF chunk shall occur in a PNG datastream. There are no ordering constraints upon the position of the eXIf beyond those imposed by the PNG specification, i.e., if present, the eXIf chunk may appear anywhere between the IHDR and IEND chunks except between IDAT chunks.