Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!texbell!chinacat!woody
From: woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal)
Newsgroups: comp.lang.postscript
Subject: Re: How to super-impose images ?
Summary: postscript images
Message-ID: <1424@chinacat.Unicom.COM>
Date: 25 Jul 90 04:33:30 GMT
References: <31377@eerie.acsu.Buffalo.EDU>
Distribution: usa
Organization: a guest of Unicom Systems Development, Austin
Lines: 29

In article <31377@eerie.acsu.Buffalo.EDU>, cchang@acsu.buffalo.edu writes:
> Please help !   We'd like to super-impose two image files.
> The codes are as following.  The image files are sparse with 
> a lot of white space.  The purpose for super-imposing is to 
> study the shifting of balck patterns in these two images.
> 
> But instead of getting the desired result, our second image 
> completely overwrites the first one.  Does anyone know how 
> to do an OR operation on two images ?  
> 
> Please post or send e-mail.  Thank you. 
> 
> p.s. May be some other netlanders will be interested in other logical
>      operations, such as AND, XOR.  So please post if you have a 
>      general solution.


Adobe uses an opaque imaging model.  That is each layer obscures the
layer underneath it.  There is no way to do AND, XOR, or OR operations.
I think that was a mistake.  I can see the point, however, when you
think about a FILM printer that does not use a memory map, but rather
uses the exposed film to store the image.  It would be impossible to
do an AND or XOR, but not an OR.  Now, the majority of the Postscript
machines are bitmapped lasers.  I think it should be allowed.  It is
one of the items on my list of things to write cexec's for...one of
these days, when I get the process down a bit better.....

Cheers
Woody