On Mon, 1 Nov 2004, Hans Hagen wrote:
Hartmut Henkel wrote:
Apart from this PNG opaque blending, there is also the "Transparency" feature in PDF (PDF Ref. chapter 7). Looks complicated. Has anybody ever played with transparency, e. g. by some \pdfliteral tricks?
sure, it's part of context for years already; one should build some additional resource dicts; i wonder if we have to go that way, since i always thought that transparency of bitmaps is a characteristic of the bitmaps image itself (so, i must look into it)
seems so yes: the alpha channel, if it would be properly extracted. Or use a separate image, tried just the maybe most trivial case: \pdfcompresslevel=0 \nopagenumbers \immediate\pdfximage {mask.jpg} \pdfximage attr {/SMask \number\pdflastximage\space 0 R} {img.jpg} \leavevmode \rlap{Hello}% \rlap{\hbox{\pdfrefximage\pdflastximage}}\bye The Hello shines through. Drawback: Seems that xpdf doesn't have any idea of /SMask yet, the example works only with acroread and gs. Instead of the mask.jpg, maybe here one could use the alpha component of a PNG (instead of stripping alpha, so that the transparent PNG parts let things shine through).
preprocessing is ok, since doing that each run takes time as well; but then we must add an howto section to the manual
how about transparent images on top of text
But there are so many special cases... Regards, Hartmut