The PNG Guide is an eBook based on Greg Roelofs' book, originally published by O'Reilly.

RGB with Transparency

As mentioned previously, PNG supports cheap transparency in RGB images via the tRNS chunk. The format is similar to that for grayscale images, except now the chunk contains three unscaled, 16-bit values (red, green, and blue), and the corresponding RGB pixel is treated as fully transparent. This option adds only 18 bytes to the image, and there are no corresponding TIFF or JPEG image types.

Last Update: 2010-Nov-26