CBS Color TV	Build your own CBS Color TV	See Color pictures on a Black & White TV
Print out your own CBS Color Wheel on your Inkjet Printer using this Color Wheel Image and 2 sheets of Overhead Projector Transparency paper
See these pictures in real CBS Color on a regular Black & White TV using your Color Wheel and a motor ( 175 line TV )
You'll need to display one of these pictures on a PC with a Video Output Card, and send it to a regular 5 inch Black & White TV with extended range Vertical Hold, see below. Color Wheel : 30 revs per second, 1800 r.p.m.
If you can't modify the TV, try the flickery demonstration. Play one of these .avi files into your Black & White TV ( 525 lines, 20 color pictures per second ) Color Wheel : 10 revs per second, 600 r.p.m.

About CBS Color:

CBS Color was the official TV Broadcast Standard of the U.S.A., as required by the F.C.C. in 1951.
The exisiting 525 line 60 Hz Black & White standard was to be replaced by the new Color TV standard, with a changeover period during which old sets could still be used and new sets would be dual-standard.
The new CBS Color system downgraded the resolution to match the British 405 line Black & White system (but see note 1).
The picture repetition rate was downgraded from 30 per second to 24 per second, a perfect match for color movie film (but see note 2). The horizontal resolution was downgraded from 430 lines to 236 lines (but see note 3) so the new system would fit in the same 4.2 MHz video bandwidth in the same 6 MHz channel.

The trade off for all this downgrading was Color! Color is so much better than Black & White. It lets you see the picture, not just the shape of it in various shades of gray, and if only CBS Color had been continued after 1951 then all of us who grew up with boring old Black & White TV in the 1950's, 60's and 70's, could have grown up watching Color TV instead !

CBS Color is Color TV on a Black & White TV Tube. Just what I always wanted! It's much simpler than the NTSC Color system which was adopted. NTSC requires the modern shadow mask color TV tube, which although it may be a better idea today, was prohibitively complex and expensive to produce in 1951, and the decision to use it held back color TV for 20 years. NTSC also requires the NTSC burst locked oscillator, synchronous quadrature detectors, and color difference matrix circuits. These may be a single chip today, but in 1951 it meant more than doubling the number of expensive vacuum tubes and their associated circuits in the TV, at a time when cost and reliability issues meant that simplicity was at a premium. CBS Color needed none of this, nor a color tube. All it needs is a Black & White TV, a motor, and a Color Wheel made from a nice shiny transparent colored plastic sheet.

The principle of CBS Color is simplicity itself. You triple the TV field rate so you can send the Red, Green & Blue primary color versions of each picture one after the other with no flicker. At home your Color Wheel turns quickly (about as fast as a regular desk fan) to put a Red filter in front of your Black & White tube while the Red signal is on the screen, continues turning to put a Green filter in front for the Green picture, and Blue for Blue. Motors of about the same speed and power as a desk fan, and the one tube circuit to synchronise it's rotation, were not a cost or complexity issue at the time. For a while you could even buy color conversion kits, where you literally attached a motor and color wheel to the side of your black & white set to turn it into a color set. How I wish I could have done that to our TV set in the 1960's !

About the CBS Color demos on this site:
The demos use the easiest versions of CBS Color that you can create with modern PC and TV equipment. Here's how they compare:

Making the Color Wheel: To make the Color Wheel large enough, use 2 sheets of Overhead Projector Transparency paper ( Letter or A4 size ). Print the semi-circular picture of half a color wheel on each sheet, at maximum size. Allow up to 5 minutes for the ink to dry.
Turn one sheet upside down and stick the 2 sheets together with clear sticky tape to make the Color Wheel. Make a small hole at the clear spot in the centre for the shaft of your motor, and cut around the edges to make it circular.

Questions or comments mailto:

Notes

Note1. This was not really a reduction in vertical resolution, because of the effect of interlace. CBS Color is much more like progressive scan TV than NTSC. CBS Color's 144 Hz interlaced scan is equivalent to a 72 Hz progressive scan. Interlace flicker would be completely absent if we took away the color wheel and looked at the tube directly. With CBS Color, interlace flicker occurs in proportion to the color saturation of the picture. The effective vertical resolution of 525 line NTSC is somewhere between 241 and 483 lines. The number of active lines per frame is 483, but NTSC flickers violently at this resolution maximum, because the frame refresh is only 30Hz, much too slow to combat flicker. To remove interlace flicker completely NTSC vertical resolution would be only 241 lines. The actual figure used is a compromise defined by the "Kell Factor", which is usually taken as being 0.7. It's an average which means that for resolutions up to 0.7 times the maximum, the interlace flicker is not too visible. So the real resolution of NTSC works out as 483 x 0.7 = 338 lines. (The horizontal resolution was calculated to match this. 4/3 x 338 lines in 52usec equals 4.2 MHz, the standard video bandwidth.)
405 line CBS Color is different. Interlace flicker occurs in proportion to the color saturation of the picture. In monochrome parts of the picture interlace flicker is much reduced because the frame rate is effectively 72 Hz. This means the vertical resolution is the same as the number of active lines in the frame, 377 lines, higher than the effective resolution of NTSC. It reduces in proportion to color saturation, to a minimum of 377 x 0.7 = 264 lines. However resolution is not so critical on highly saturated colors, especially blue and yellow, so this reduction will often not be apparent. If we say that most pictures will average 50% saturation, the result is an average effective resolution of 321 lines, almost identical to NTSC.

Note 2. This does not actually have to be seen as a downgrade either. CBS Color's 48 Hz field refresh is just as good at producing a flicker free picture as the the 48 Hz shutter frequency of the cinema, or the 50 Hz refresh used with all European TV systems. Furthermore, the effective flicker frequency depends on color saturation. The fundamental flicker frequency is 144 Hz, falling to 48 Hz for fully saturated colors. Most picture content will have an effective flicker frequency somewhere between these two limits, and comparable with NTSC's 60 Hz.

Note 3. "Dot Interlace" was introduced to CBS Color. This takes advantage of CBS Color's inherent field rate overhead to share the horizontal detail across successive fields. Dot Interlace almost doubles the horizontal resolution from 236 lines to 405 lines. (The fact that this is the same as the number of scanning lines is just a coincidence.) This is higher than the resolution of NTSC Color which is about 370 lines in practise due to the subcarrier notch filter in the color decoder.

As you can see, the CBS Color system was very well thought out, and provided pictures with vertical and horizontal resolution equal to or better than NTSC within the same bandwidth, inspite of using nearly 3 times the picture frequency.

CBS Color is also completely free of a long list of problems which dogged NTSC and the shadowmask tube for another 30 years:

• No Hue errors
• No Cross-color
• Color noise no worse than Black & White
• No Color Balance errors
• No Convergence errors
• No Purity errors

CBS Color was free from all of these problems from the outset.

Note: Some parts of this page are incomplete, as it is still under construction.
Last updated December 8, 2002.