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. |