Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!tektronix!tekcrl!tekfdi!videovax!bill From: bill@videovax.Tek.COM (William K. McFadden) Newsgroups: sci.misc Subject: Re: Color Message-ID: <4715@videovax.Tek.COM> Date: Fri, 4-Dec-87 12:58:27 EST Article-I.D.: videovax.4715 Posted: Fri Dec 4 12:58:27 1987 Date-Received: Thu, 10-Dec-87 20:34:34 EST References: <162300002@uiucdcsb> Reply-To: bill@videovax.Tek.COM (William K. McFadden) Organization: Tektronix Television Systems, Beaverton, Oregon Lines: 42 In article <162300002@uiucdcsb> kadie@uiucdcsb.cs.uiuc.edu writes: >I've got two miscellaneous science questions. >1) On TV's and computers screens, why is it RGB (red, green, blue) >instead of RYB (red, yellow, blue) the primary colors? >2) Some light wave length produces the color green. A mixture of >the wave lengths of blue and yellow also produces green. >Even though these two greens are indistinguishable to our eyes, are there >(could there be) instruments that distinguish them? (1) You're talking about two different media here. A TV monitor produces color by mixing red, green, and blue light together in varying proportions. This is called additive color because you start out with black (no light) and add light to make color. On the other hand, when you produce color by mixing paints, it is called subtractive color because you start out with white (all colors) and remove light to make color. For example, red paint absorbes all colors except red so that when you shine a white light on it, it reflects the red component and absorbes the rest. If you shine a blue light on it, it looks black because there is no red component to reflect. It simply absorbes all the blue light and reflects nothing. Since subtractive systems work differently, they need different primary colors than those used in additive systems. For example, color ink jet printers use primary colors of magenta (reddish), yellow, and cyan (bluish). (2) Be careful, you are talking about subtractive colors, so to say you are mixing blue and yellow wavelengths to produce green is not correct (see (1)). Let's try a different example. If you mix red light with green light (as in a CRT) you get yellow. If you look at this light spectrally (e.g., using a prism), you will see a peak in the red wavelengths and another in the green. But it looks yellow to our eyes because our eyes are fooled (don't ask me why our eyes do this). In other words, the mixture of two light frequencies causes our eyes to perceive a new frequency (yellow). Consider us lucky our eyes do this, because otherwise color TV would have been impossible (or at least terribly difficult). -- Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-639 Beaverton, OR 97077 UUCP: ...{hplabs,uw-beaver,decvax}!tektronix!videovax!bill GTE: (503) 627-6920 "How can I prove I am not crazy to people who are?"