[comp.lang.postscript] how should imagemask display?

bradlee@cg-atla.UUCP (Rob Bradlee) (12/13/90)

If I have an image that is displayed with the imagemask operator, what
should it look like on a screen diplay.  It seems to me that if I
put it over a solid block of color that the color should show through
the non-black pixels.  However, one of our systems in development is
making the non-black pixels white.  Your opinions, please.

					Rob

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glenn@heaven.woodside.ca.us (Glenn Reid) (12/17/90)

In article <9313@cg-atla.UUCP> bradlee@cg-atla.UUCP (Rob Bradlee) writes:
>If I have an image that is displayed with the imagemask operator, what
>should it look like on a screen diplay.  It seems to me that if I
>put it over a solid block of color that the color should show through
>the non-black pixels.  However, one of our systems in development is
>making the non-black pixels white.  Your opinions, please.

My opinion is that the non-black pixels should show through.  That's
the whole point of "imagemask".  In fact, the pixels in "imagemask"
are not actually colored, they are a mask through which you pour the
current color from the graphics state onto the current page or screen
or frame buffer or whatever.  The semantics of a mask imply that there
will be places where no color is applied.

I'd say you have a bug in your system in development.

Make sure you have the "invert" parameter to "imagemask" set the way
you intend (in fact, try reversing it if you're not sure).  This could
reverse the sense of your test and paint the wrong thing.  But other
than that, your impression seems right to me.

/Glenn
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 Glenn Reid				RightBrain Software
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