Hawes Mechanical Television Archive by James T. Hawes, AA9DT
Two-Color TV, Part 1

What is Two-Color TV?

Complementary colors. We're familiar with three-color TV. After all, it's been available since 1951 or so. (At least in the US.) Two-color TV is almost the same thing, only it uses two primary colors. Yes, that's possible! But how could we build full-color images with just two primary colors? Simple. All we need is a TV set that displays two complementary colors. These colors become our primaries, replacing red, blue and green.

Art: fraction '2/3' on field of 
           question marks.

The only requirement is that some combination of the two colors produces white. Preferably, white should emerge when the two colors mix in near-equal quantities. In typical applications, the two colors should produce natural-looking flesh tones. For example, red-orange and cyan are most desirable two colors. Red-orange makes realistic flesh tones, while cyan makes acceptable (if imperfect) skies and grass.

Advantages & Disadvantages

What is the disadvantage of two-color TV? The gamut or number of possible colors is lower than with three colors. Then why would we want to use two colors? For several reasons...

  • Simplicity. Two colors reduce circuit complexity by 30 percent.

  • Bandwidth. With only two colors, we can fit a TV signal into less space. For this reason, Even three-color television systems such as NTSC and PAL only transmit two colors. (These systems further reduce bandwidth by matrixing two colors onto one signal.)

  • Low noise. The narrower bandwidth means that we have a lower-noise signal. This signal travels farther before it disappears into the background static.

  • Research. Viewers mentally fill in missing colors. Research by Edwin Land of Polaroid fame proves this phenomenon. More later.

  • A special advantage for field-sequential displays: Dramatically less flicker than with three-color TVs.

Wizard of Oz 
            shots off two-color TV by Cliff Benham: Dorothy, Scarecrow Cliff Benham's famous, 2-color TV with Dorothy from The Wizard of Oz. Mouse over for the Scarecrow.

Flicker Reduction

For field-sequential TV. Of all these advantages, flicker reduction is the most important. Why? Because flicker is the most irritating disadvantage of field sequential TV. Field-sequential TV is the “CBS method” that DLP projectors and 3D games use. In history, Col-R-Tel converters (not the CBS System) were the most prominent field-sequential technology. Cameras that operated on the Col-R-Tel standard journeyed to the moon with Apollo astronauts. (See Moon Col-R-Tel.)

For those who haven't read our Col-R-Tel pages: Col-R-Tel is an add-on color wheel and chroma decoder for U.S. monochrome TVs. With Col-R-Tel, a monochrome TV can decode standard color telecasts and display them in full color. Col-R-Tel's main flaw is that it can only display one color at a time. The viewer notices this effect as flicker. As we'll see, Spectrac, a later converter, solved the flicker problem. In fact, Spectrac proved that two colors could reduce flicker while depicting natural-looking people and scenes. Meanwhile, Spectrac also introduced a novel, two-level scanning belt that replaces the color wheel. Compared to the wheel, the belt is smaller, runs more quietly and draws less current.

Wizard of Oz photos off two-color TV by Cliff Benham Benham 2-color TV displays witch from The Wizard of Oz. Mouse over for ruby slippers.



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Page Directory

What is Two-Color TV

Advantages & Disadvantages

Flicker Reduction

Col-R-Tel vs. Spectrac

Col-R-Tel flicker

Spectrac

2-color gamut

History

2-color NTSC

2-color Col-R-Tel

Assembly

Schematic

TV System Flicker Comparison

2.5-Color TV

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Text, design, table & original graphics, copyright © 2011 by James T. Hawes. All rights reserved.
Two-color, Wizard of Oz photos copyright © 2011 by Cliff Benham. All rights reserved.

•URL: http://www.hawestv.com/mtv_2color/mtv_2color.htmWebmaster: James T. Hawes
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