Lists all PNG tag identifiers.

Values:

IGMDTAG_ID_PNG_FORMAT	PNG metadata format identifier.
IGMDTAG_ID_PNG_HEADER	Header information.
IGMDTAG_ID_PNG_TRANSPARENCY	Transparency information.
IGMDTAG_ID_PNG_GAMMA	Gamma information.
IGMDTAG_ID_PNG_CHROMATICITIES	Chromaticities information.
IGMDTAG_ID_PNG_SRGB	Standard RGB information.
IGMDTAG_ID_PNG_ICC_PROFILE	ICC profile information.
IGMDTAG_ID_PNG_BACKGROUND	Background information.
IGMDTAG_ID_PNG_SIGNIFICANT_BITS	Significant bits information.
IGMDTAG_ID_PNG_SUGGESTED_PALETTE	Suggested palette information.
IGMDTAG_ID_PNG_HISTOGRAM	Histogram information.
IGMDTAG_ID_PNG_TIME	Time image last modification information.
IGMDTAG_ID_PNG_TEXT	Text data information.
IGMDTAG_ID_PNG_COMPRESSED_TEXT	Compressed textual data information.
IGMDTAG_ID_PNG_INTERNATIONAL_TEXT	International textual data information.
IGMDTAG_ID_PNG_CALIBRATION	Calibration information.
IGMDTAG_ID_PNG_PHYSICAL_SCALE	Physical scale information.
IGMDTAG_ID_PNG_GIF_APP_EXT	GIF application extension information.
IGMDTAG_ID_PNG_GIF_CONTROL	GIF control information.
IGMDTAG_ID_PNG_IMAGE_OFFSET	Image offset.
IGMDTAG_ID_PNG_FRACTAL_PARAMETERS	Fractal parameters information.
IGMDTAG_ID_PNG_GIF_TEXT_EXT	Gif text extension information.
IGMDTAG_ID_PNG_RESOLUTION	Resolution information.