Xref: utzoo comp.graphics:4017 comp.windows.x:7059
Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!oliveb!sun!falk
From: falk@sun.uucp (Ed Falk)
Newsgroups: comp.graphics,comp.windows.x
Subject: Re: Luminance from RGB
Message-ID: <83604@sun.uucp>
Date: 4 Jan 89 04:19:22 GMT
References: <23105@apple.Apple.COM> <2263@eos.UUCP>
Organization: Sun Microsystems, Inc. - Mtn View, CA
Lines: 19

In article <2263@eos.UUCP>, jbm@eos.UUCP (Jeffrey Mulligan) writes:
> From article <23105@apple.Apple.COM>, by turk@Apple.COM (Ken "Turk" Turkowski):
> > Y = (R + 2G + B) / 4
> Y = 2R + 5G + B

Yeesh, you people.  Why do you need to simplify it?  Are you going to be
doing these calculations by hand?  Get a calculator or something.

If you *must* do it in integer for speed reasons, do it this way:

    out = (77*r + 151*g + 28*b)/256 ;	/* NTSC weights (.3,.59,.11)*/

The results are correct to four decimal places and the divide is replaced
by a right-shift in a decent compiler and a byte-move in a good compiler.

-- 
		-ed falk, sun microsystems
		 sun!falk, falk@sun.com
		 card-carrying ACLU member.