Public comments on this W3C Recommendation are welcome. Please send them to the archived list png-group@w3.org .
For the tRNS chunk, Colour type 2, a typographical error was introduced in the second edition of PNG: the blue and green channels were switched. The first edition of PNG had the correct order, Red, Green, Blue. This is the same order as is used throughout the specification, and implementations have silently corrected for the obvious error.
In section 11.3.2.1 tRNS Transparency change:
| Colour type 0 | |
|---|---|
| Grey sample value | 2 bytes |
| Colour type 2 | |
| Red sample value | 2 bytes |
| Blue sample value | 2 bytes |
| Green sample value | 2 bytes |
| Colour type 3 | |
| Alpha for palette index 0 | 1 byte |
| Alpha for palette index 1 | 1 byte |
| ...etc... | 1 byte |
to:
| Colour type 0 | |
|---|---|
| Grey sample value | 2 bytes |
| Colour type 2 | |
| Red sample value | 2 bytes |
| Green sample value | 2 bytes |
| Blue sample value | 2 bytes |
| Colour type 3 | |
| Alpha for palette index 0 | 1 byte |
| Alpha for palette index 1 | 1 byte |
| ...etc... | 1 byte |