SUMMARY: Grey Level on a monochrom screen.

From: Aadne Hestenes Spt (
Date: Tue Jun 09 1992 - 10:10:54 CDT

May original question was as follows:

> I have an SS2 with the standard monochrom screen and framebuffer,
> and I may want to swap the existing framebuffer with a 8bit framebuffer,
> in order to display 256 greylevels.
> I know this is possible by using the GX framebuffer,
> but there may be other possibilities too, and cheaper ...
> Please mail me if you know anything, and I make a summary.
I got the following answers:

>From, (originally written in norwegian) :

This depends on your monitor. If you have a new one, it will run on 76 HZ.
A standard 8bits framebuffer (cgthree) is running 66 HZ.
Thus this combination is not compatible, but if you have an old monochrom
monitor this will not be a problem.

- Sven
>From :

Just connecting the B/W monitor to any colour framebuffer works.

BUT: what you get is essentially a Black-and-Green monitor (though it
displays in white...), because the monitor only senses the "green" pin
in the RGB connector from the framebuffer. This causes some interesting
effects in displaying colour images since all red and blue hues come
out black.

Starting OW with the -grayvis option is less than perfect because it
then assumes you have full colour but want it all in grey, so it
outputs everything "averaged" to balance red, green and blue. You only
get one third of the signal which appears very dark on the screen.
(This wouldn't be a problem if human perception of brightness was
linear. However, it is more logarithmic, so a colour scheme designed to
give nice contrasts in colour comes our too dark on a "fake"

The only viable option is to run OW in full colour and then use the
setups (or .Xdefaults) to select background and window-frame colours
that are in reality pure shades of green. It will look like vomit if
you ever display it on a real colour screen, but it does work

 Ericsson Telecom AB, EO/ETX/TX/ZD
 Phone: +46 8 719 4881



I had a mono monitor (365-1071-01) plugged into my cgthree for a while before
my colour monitor arrived. Worked fine.

George D M Ross, Department of Computer Science, University of Edinburgh
     Kings Buildings, Mayfield Road, Edinburgh, Scotland, EH9 3JZ
Tel: 031-650 5147   Internet:   JANET:



The cg3 framebuffer (8-bit rgb, no accelerator) should be cheaper than a GX, and either one should be capable of driving a grayscale monitor (usually from the red output); however I don't think either of them can drive the "standard monochrome" monitor used with the bw2 framebuffer.

A grayscale monitor should be cheaper than a color monitor of the same size, but may be more expensive than the "monochrome" monitor.


Thanks to all.

Best Regards ---------------------------------------------------------------------------- Adne Hestenes, Tlf: +47-83-84500 Spacetec a.s, Fax: +47-83-55859 Box 585, email: 9001 Tromsoe, NORWAY ----------------------------------------------------------------------------

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