Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcdc!hpfcdq!benji
From: benji@hpfcdq.HP.COM (Jeff Benjamin)
Newsgroups: comp.graphics
Subject: Re: Mapping Color to Black and White
Message-ID: <390027@hpfcdq.HP.COM>
Date: 1 Apr 89 01:29:49 GMT
References: <2148@viscous.sco.COM>
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 20

> I am trying to take a color image with know RGB values
> and translate it to a black and white image. 
> 
> Could anyone give me some help on this?  Do you take the normalized
> vector for a particular color and this is your percentage
> in the shade of grey?   (r * 0.??? + g * 0.??? + b * 0.???) = grey.
> I get the impression that the various percentages for r, g, and b
> should be about .300, .450, and .250 respectively.

You're close...the equation you want turns out to be:

	I = 0.30 * r + 0.59 * g + 0.11 * b

This takes eye sensitivity to different colors into account.  I don't
know much about the derivation of this; maybe someone else can elaborate.

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Jeff Benjamin                         {ucbvax,hplabs}!hpfcla!benji
Graphics Technology Division          benji%hpfcla@hplabs.HP.COM
Hewlett Packard Co.                   Fort Collins, Colorado