This specification defines a mechanism for storing images that use the Reference PQ EOTF specified in [[!BT2100-1]] in the Portable Network Graphics (PNG) format (specified in [[!PNG]]), without modification to existing chunks or the introduction of new chunks.
This specification is intended to be published as a Working Group Note.
gAMA chunk of the Portable Network Graphics (PNG) format (specified in [[!PNG]]) parameterizes the transfer
function of the image as a power law. As such, it cannot model the Reference PQ EOTF specified in [[!BT2100-1]], which is
commonly used for HDR images.
This specification uses the existing
iCCP chunk to unambiguously signal the color system of an image that uses
the Reference PQ EOTF specified in [[!BT2100-1]]. It also allows graceful processing by decoders that do not conform to this
specification by recommending fallback values for the
cHRM chunk, and embedded ICC
The file SHALL conform to [[!PNG]].
The image type SHALL be
The image SHALL conform to one of the Pixel Encoding Systems specified in the table below.
The file SHALL contain an
iCCP chunk, constrained as follows:
iCCPchunk SHALL be set as specified by the table below according to the Pixel Encoding System of the image; and
iCCPchunk SHOULD contained one of the ICC profiles specified by the table below according to the Pixel Encoding System of the image; and
cHRM chunk and the
gAMA chunk of the file SHOULD be set as specified by the table below
according to the Pixel Encoding System of the image.
|Pixel Encoding System||
|[[!BT2100-1]], using the Reference PQ EOTF and full-range quantization||
gAMA chunk and embedded ICC profile specified in the table above are not accurate, and their
processing is not required to reproduce the image as intended by the author. They are provided as fallback for implementations
that do not recognize the semantics associated with a
iCCP Chunk Profile Names defined by this specification.
Future versions of this specification might include additional ICC profiles, e.g. to reflect improvements in ICC profile
This specification does not constrain bit depth.