Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!mtune!mtuxo!homxb!houxm!homxc!cram
From: cram@homxc.UUCP (M.HOWARD)
Newsgroups: comp.graphics
Subject: Re: N-bit greyscale to n-bit greyscale
Message-ID: <267@homxc.UUCP>
Date: Wed, 29-Apr-87 17:31:58 EDT
Article-I.D.: homxc.267
Posted: Wed Apr 29 17:31:58 1987
Date-Received: Sat, 2-May-87 05:19:00 EDT
References: <4231@nsc.nsc.com> <3318@pogo.TEK.COM>
Organization: AT&T Bell Laboratories, Holmdel
Lines: 25
Summary: Y is luminance in NTSC

In article <3318@pogo.TEK.COM>, curtj@pogo.TEK.COM (Curt Jutzi) writes:
> In article <4231@nsc.nsc.com> misha@nsc.nsc.com (Michael Umansky) writes:
> >Hello.
> >Example:
> >	I have a bitmap image with 8 bits per pixel.
> >	Now, I have a monochrome TTL monitor which requires 1 bit per pixel.
> >	I need to convert the 8-bit-pixel image to 1-bit-pixel image and
> >	still be able to distinguish original shapes and lines.
> >
> 
> 	The way I have always seen it done is by taking the (RGB) values
> 	and converting them to (YIQ).  From this format you take the 
> 	intensity (I believe that it is "I" component) which should go
> 	from 0..255, and use a dithering scheme to approximate the 
> 	half-tone.

	Y is the luminance (intensity) component in NTSC color encoding.
	I (Inphase) and Q (Quadrature) are the chroma components that are
	encoded on the subcarrier.  Y is defined by:

		Y = .30*Red + .59*Green + .11*Blue

						Marc W. Howard
						AT&T Bell Labs, Holmdel NJ
						...ihnp4!homxc!cram