2014.01.18 18:24 "[Tiff] Adding alpha to palette files", by John Hawley

2014.01.19 08:39 "Re: [Tiff] Adding alpha to palette files", by Joris Van Damme

John,

Bob wrote:

I strongly recommend not trying to create a palette image with an alpha channel.

I second that.

I don't think it's legit TIFF, either. Whilst a lot of what we do is "interpolation" from the original specification, because that specification is mostly an enumeration of a few possible combinations rather then a thorough actual specification of the building blocks, it's not unambiguously clear (at least to me) how you would go about adding an alpha channel to a palette image, or to a palette. I don't know of any TIFF codec, including my own, that would support it.

You could do full RGB with an alpha channel, effortlessly. Or you could add a private tag that to your software, privately, signals a transparent color index into the palette, but then normal rendering would no longer closely resemble your application-private rendering of such TIFFs.

Joris Van Damme
AWare Systems
info@awaresystems.be
http://www.awaresystems.be/