🚀 go-pugleaf

In article <4829@helios.ee.lbl.gov> Jef Poskanzer <jef@well.sf.ca.us> writes:
>I want to do a PostScript image operation with a mask.  I do not mean
>imagemask -- that paints a 1-bit deep image with 1's getting the
>current color and 0's getting left alone.  What I want to do is paint
>an N-bit image, and have a separate 1-bit mask controlling which parts
>of the N-bit image get transferred and which parts get ignored.
>
>I could do it by lasooing the border of the 1-bit mask and converting
>it into a clipping list, but that seems extremely grody.  Does anyone
>see a better way?

That is the only way to do it "right." A simpler and faster technique
would work if you happen to know that the background is a particular
uniform color.  Assuming wlog that the background is white, image the
grey level image, then image the clipping bitmap over it, inverted,
with currentgray set to white.  That will "erase" the image wherever
you didn't want it painted. 

- Geof
-- 
geof@aurora.com / aurora!geof@decwrl.dec.com / geof%aurora.com@decwrl.dec.com