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From: ao@tub.UUCP
Newsgroups: comp.graphics
Subject: Re: Simple RGB to Gray scale question - (nf)
Message-ID: <48300002@tub.UUCP>
Date: Mon, 2-Mar-87 08:09:00 EST
Article-I.D.: tub.48300002
Posted: Mon Mar  2 08:09:00 1987
Date-Received: Fri, 6-Mar-87 06:40:22 EST
References: <718@hp-sdd.UUCP>
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Nf-ID: #R:hp-sdd:-71800:tub:48300002:000:871
Nf-From: tub!ao    Mar  2 14:09:00 1987

> /***** tub:comp.graph / hp-sdd!nick /  6:48 pm  Feb 25, 1987*/
> 
> How does one convert a pixel defined by an R, G, B value into
> a single Gray level?
> 
> Gray = (R+G+B) / 3  ???
> 

You wouldn't be able to distinguish between the New York Jets and
Giants ( if I remember correctly ) seen on a black and white TV monitor.

> It seems like the R, G, B components should have different weights since
> I'm aware that the eye is less sensitive to blue light.
> 
In the YIQ model, that is used in commercial color TV, the Y-component
of the color signal is shown on a B/W screen.
It is defined as:

Y = 0.3 * Red + 0.59 * Green + 0.11 * Blue

and matches the luminosity response curve of the eye.

Expierences are good with that formula used in a
GKS to PostScript filter for our LaserWriter.

Arnfried Ossen, ao @ tub.UUCP, Technische Universitaet Berlin, West Germany