Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!bragi!dj
From: dj@bragi.ctron.com (DJ Delorie)
Newsgroups: comp.os.msdos.programmer
Subject: Re: MSDOS monochrome displays?
Message-ID: <1399@bragi.ctron.com>
Date: 4 Apr 91 20:56:09 GMT
References: <3586@naucse.cse.nau.edu>
Organization: None whatsoever
Lines: 31

In article <3586@naucse.cse.nau.edu> rrw@naucse.cse.nau.edu (Robert Wier) writes:
>
> OK, I'm confused.  I have a situation where I'd like to display
> monochrome graphics in at least 16 shades of gray, preferably
> 256 shades of gray.  This is data received from the GOES series
> of weather satellites.

> I have several questions.  It would seem reasonable that an EGA
> board which can display 16 colors SHOULD be able to display 16
> shades of gray.

An EGA board with a color monitor can display up to four shades of
grey at a time.  The reason?  The TTL signals for an EGA supply two
bits per color (R,G,B).  Total of 64 colors, four of which are grey.

An EGA with a MONOCHROME EGA monitor can display up to sixteen greys
at a time, but the EGA card itself thinks they're colors.  The monitor
converts the TTL signals to greys instead of RGB.

An EGA with a vanilla mono monitor (ie: from an MDA) is limited to
four greys again, because the monitor only watches two of the TTL
signals.

A VGA can display up to 64 greys at a time, as it's palette has six
bits per color, regardless of the type of VGA monitor you attach to
it.  This still gives you 192 pixel values left in 256 color mode to
do simulated color if you want.  Of course, 16 greys in 16-color mode
is no problem for VGA.

DJ
dj@ctron.com