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Re: # of shades of gray



>>>>> "Gerald" == Gerald Luther Graef <ggraef@alpha1.csd.uwm.edu> writes:
In article <4dkflg$m8u@uwm.edu> ggraef@alpha1.csd.uwm.edu (Gerald Luther Graef) writes:

    Gerald> I've been experiementing with NIH-image and executor.  The
    Gerald> images I'm looking at are 256 shade grayscale.
    Gerald> Unfortunately, I can only get executor to display in (I
    Gerald> think) 64 colors (at least, the image looks quite muddy
    Gerald> compared to NIH-image on a Mac.  Is it possible to display
    Gerald> at 256 shades?  Or does it do it now and my setup is
    Gerald> wrong?

The problem has to do with the way Executor accesses the Digital to
Analog Converter (DAC) that VGA based screens use to display colors.

Mat Hostetter says:

``"Standard" DACs are 6-bit, so you can get 64 visibly distinct shades of
  gray.  Some DACs support 8-bit, which let you get 256 shades of gray.
  8-bit DACs (when present) can be manipulated with a VBE 2.0 extension
  Executor doesn't yet use.''

The problem is that VBE 2.0 is sufficiently new that we don't yet have
drivers for our machines that provide that particular piece of
functionality, so although we could put code into Executor to detect
this extension and use it when present, we wouldn't be able to test
it.  There is a new version of UniVBE due out real soon now and that
may change things.  We hope to support 8-bit DACs (when they're
present) by the time Executor 2 ships.

    Gerald> Thanks...  Gerry

I'm cc'ing this to "questions@ardi.com" so our question + FAQ person
can add this to our FAQ.  Thank *you* for asking.

--Cliff
ctm@ardi.com


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