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From: paul@imsvax.UUCP
Newsgroups: comp.graphics
Subject: Re: Simple RGB to Gray scale question
Message-ID: <695@imsvax.UUCP>
Date: Fri, 27-Feb-87 14:55:06 EST
Article-I.D.: imsvax.695
Posted: Fri Feb 27 14:55:06 1987
Date-Received: Sun, 1-Mar-87 12:40:56 EST
References: <718@hp-sdd.HP.COM>
Organization: IMS Inc, Rockville MD
Lines: 31
Keywords: RGB grayscale

Nick V. Flor / ..hplabs!hp-sdd!nick / Hewlett Packard, San Diego Division
asks:

> How does one convert a pixel defined by an R, G, B value into
> a single Gray level?

> Gray = (R+G+B) / 3  ???

> 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.

You are quite right that different weights are generally used.  The weights
used in NTSC TV signals (which allow one to view a color signal on a
black-and-white set) are:

   Luminance (gray) = 0.30 red  +  0.59 green  +  0.11 blue

I think this is what you want, although a great deal of work is still being
done in this field.
A good discussion of some of the background for these factors is in:

"Digital Coding of Color Video Signals - A Review", Limb et al., IEEE
Transactions on Communications, vol. COM-25, pp. 1349-1384, Nov. 1977.

Hope this helps!

-- 
                                Paul Knight

           God created man in his own image.
           Man, being a grateful creature, returned the favor.