2005.11.03 15:53 "Re: [Tiff] Writing bilevel and transparent TIFFs efficiently", by Gerben Vos

I'm trying to write a bilevel image as a transparent TIFF. So one of the colors is always transparent, and the other is opaque. What is the best way to do this? I can't use G3 or G4 because the colors are not necessarily black and white. The one option I see is to write an RGB image with an associated alpha but that doesn't seem very efficient. Is there a better way to do this? What type of compression should be used?

I guess it depends mostly on what is supported by the application which will receive the TIFF.

One other thing you could try is to have a G3/G4 transparency mask (Photometric = 4, NewSubfileType has bit 2 set), and another image in the TIFF file containing a single coloured pixel, with the resolutions matched so that the images are the same size. However, I can't find anything in the spec about how the two images are to be associated with each other, and I doubt this format is supported widely, or at all.

                                        Gerben Vos.