PDFlib, transparency and TIFF images

Hi everyone - hope there's someone good at PDFlib out there… I'm trying to use a picture, a TIFF image, with transparency, in a PDF created by a PHP-script... The manual says that only "explicit transparency" can be used when working with TIFF images, and that this operation requires two steps… But then the manual loses me, and I don't understand what the "two steps" that seems to be required actually meens… Isn't it sufficiant to have a TIFF image with transparency, or do I have to have some kind of second image and use that as some kind of mask to acquire transparency effects? Will this, if so, require two image files per image instead as one? Hope this is not OT, if so, i apologize… Sincerely Victor Spång Arthursson Sweden / Denmark