The 1954 Tournament of
Roses (aka Rose
Bowl Parade) was famously the world's first national
commercial color television broadcast, provided by the National
Broadcasting Company (NBC). Prior to the
Television Systems Committee) finally settling on an all-electronic scheme for
TV sets, many electro-mechanical and electro-optical types were developed. The
integrated RGB (red, green, blue) color gun within a cathode ray tube (CRT)
was a relatively new concept in 1949. This article presents some of the propositions
by the two major research and development players at the time: RCA and CBS.
They might seem ridiculous in the light of knowledge available now, but a round
wheel wasn't immediately obvious to Oog sitting in his cave, trying to figure
out an easier way to transport that mastodon carcass.
I wonder if Figure 9 was an early laboratory version of the
By M. S. Kay
Fig. 1 - The internal construction of the RCA three-color
television pickup camera unit.
A review of RCA and CBS color systems. Will either of these or some other
color system be chosen? Decision is, at present, in hands of FCC. It is likely
that final decision will be postponed indefinitely to permit further design
development and improvement.
Everyone knows that someday all television will be color television. Of this,
there is little doubt or dispute. The big question at the moment, however, is
When? Is color television ready now or are we technically premature? Can color
television be made compatible with our present black-and-white system or will
it require an entirely new set of standards, thereby obsoleting all present
sets? It is for the purpose of finding answers to these questions before the
final u.h.f. allocations are made that the present hearings are being conducted
by the Federal Communications Commission.
One of the most important stipulations that was made by the FCC concerning
the adoption of any color television system was that it should be as nearly
compatible to our present black-and-white system as possible. It is definitely
not desired that the 2,500,000 or more sets now in the hands of the public be
made obsolete by the introduction of a color television system.
The two major systems that are receiving the most consideration are those
put forth by RCA and CBS. The CBS system is essentially the same one developed
and demonstrated by this firm several years ago. The RCA system, however, is
Fig. 2 - Block diagram of a possible two-color TV receiver.
Fig. 3 - Block diagram of RCA's color television transmitter.
Fig. 4 - Method of operation employed in the sampler
Fig. 5 - A block diagram of a color television receiver.
Fig. 6 - Operation of the receiving set sampler system.
To start at the beginning, let us investigate a few facts about color. Color,
physicists tell us, is a property of light. If we take sunlight and pass it
through a glass prism, a variety of colors are produced. White sunlight contains
all colors but, due to the limitations of the human eye and the fact that the
colors produced by the prism blend into each other, we can count only seven
fairly distinct colors. Upon closer inspection of this color distribution, innumerable
fine gradations may be distinguished, both between different colors and within
anyone color itself. For example, red when it first becomes definitely distinguishable
from its neighbor, orange, possesses a different shade than it does at the other
end of the red band, where the infrared wavelengths are approached.
Now all the various shades and tints that are contained in the spectrum can
be reproduced by combinations of three pure colors. The colors are red, green,
and blue and these have been named the "primary" colors. To obtain a certain
color, we combine the primary colors in definite proportions. Yellow may be
derived from combinations of red and green; orange by other proportions of the
same two colors; white by using all three, etc. These facts have been put to
use in color television by breaking down the light received from a scene into
its primary components at the transmitter and then recombining them at the receiver.
In the RCA system, the scene to be televised is picked up by a color camera
containing three camera tubes. The light entering the camera is passed through
special mirrors (known technically as dichroic mirrors) which possess the property
of being able to reflect one color but pass all others. Thus, a red dichroic
mirror will reflect red light, but permit all other light to pass through. In
the color camera, red and blue dichroic mirrors are arranged in the manner shown
in Fig. 1. The portion of the incoming light which is red is reflected
by the red dichroic mirror (and a second reflecting mirror) into one camera
tube. The blue portion of the incoming light is reflected into a second camera
tube by the blue dichroic mirror (and a second reflecting mirror). What remains
of the light after passage through the two dichroic mirrors, green, is received
by the third camera tube. In this manner every bit of light reaching the camera
is sorted into its primary color components.
The output from each camera is now transferred through separate low-pass
filters (which pass only video signals having frequencies up to two megacycles)
to an electronic sampling tube. See Fig. 3. At the same time this is happening,
portions of the three-color signals from the camera are combined in electronic
Adder No.2 and passed through a bandpass filter where video frequencies up to
2 mc. are suppressed and those from 2 to 4 mc. are transmitted. This system
of dividing the color signals into separate low- and high-frequency components
and then combining all of the high-frequency components together is known as
a mixed-high system. Why this particular method was chosen will be indicated
The mixed-high frequencies are fed to Adder No.1 which is also receiving
signals from the electronic sampler. However, while the mixed-high frequencies
are arriving in a continuous stream, the low-frequencies are arriving in spurts,
from the electronic sampler, in the form of short pulses. Within the sampler,
an electron beam is revolving at a rate of 3.8 million times per second. The
beam thus comes in contact with the color signal from each camera 3.8 million
times in each second providing Adder No.1 with this many samples from each color,
one sample arriving every 0.263 microsecond (1/3.8 = 0.263). Fig. 4 shows
the output of the sampler for a short period of time. In Fig. 4A, the output
of the sampler for the green signal is shown. A green sample (pulse of voltage
from the signal fed to the sampler by the camera receiving the green portion
of the incoming light) appears every 0.263 microseconds.
At a time 0.0877 microsecond after the first green sample, a sample is taken
of the voltage from the camera receiving the red rays of light. The red samples
themselves, however, are spaced 0.263 microsecond apart. Blue samples are taken
at the same rate as the red and green samples and appear 0.0877 microsecond
after a red pulse of voltage. The composite sequence of these voltage pulses
is shown in Fig. 4D. For any particular scene, the strength of each pulse
would depend, of course, on the amount and shading of the color rays reaching
Fig. 7 - RCA color TV direct-view picture-reproducing
system using 3 kinescopes and two dichroic mirrors.
The pulses at the output of the sampler tube are fed to Adder No. 1 where
they are combined with the mixed-highs signal. Both signals are applied now
to a low-pass filter (passing 0-4 mc.) where the pulses of voltage from the
electronic sampler are smoothed out. Each of the smoothed out pulses now becomes
a sine wave having a frequency of 3.8 mc. See Fig. 4E, F, and G. It should
be noted in these sine waves that when any one color signal reaches its maximum
value, the other two color signals are passing through zero. This is important
and insures that when the signals are again sampled at the receiver, that only
one color is obtained during each sampling.
While the three sine waves are shown separately in Fig. 4E, F, and G,
they are actually combined in the low-pass filter to form the composite signal
shown in Fig. 4H. It is this composite signal which combines with the mixed-highs
signal to provide the complete video signal. The remainder of the transmitter
now follows the usual sequence of amplifying this voltage, impressing it onto
an r.f. carrier and sending it out over the air to the receiver.
Color Television Reception
The color television signal at the receiver (together with the accompanying
sound) is received and amplified by a series of stages which, up to the second
detector, are similar in all respects to the same stages found in present black-and-white
television receivers. Thus, there is an r.f. amplifier, a mixer, a high-frequency
local oscillator, a series of video i.f. stages and a conventional second detector.
See Fig. 5. The same is true of the audio system with its i.f. amplifiers,
discriminator, audio amplifiers, and speaker.
Now, the video signal at the output of the second detector consists of the
composite color signal, as shown previously in Fig. 4H, plus the vertical
and horizontal synchronizing pulses which are required to keep the receiver
image in step with the transmitter image. Part of the signal is applied to a
sync separator stage where the sync pulses are divorced from the rest of the
signal and then fed to sawtooth deflecting circuits where they lock-in the sweep
oscillators. This, again, does not differ from conventional black-and-white
television receiver practice.
The rest of the signal from the video second detector is fed to a sampler
tube which is similar to the sampler tube employed at the transmitter. Every
0.0877 microsecond, the sampler tube samples the composite signal, producing
the narrow pulses shown in Fig. 6A. The amplitude of each sample will depend
upon the strength of the composite wave at that particular instant. This same
stipulation was true at the transmitter, it will be remembered.
Fig. 8 - RCA color television projection picture-reproducing
system using three projection kinescopes, reflective optics, and two dichroic
The sampler sends these pulses to each of the video amplifiers and its associated
cathode-ray tube in succession. Thus, looking at Fig. 6A, the green pulse
goes to the video amplifier system which is associated with the cathode-ray
tube emitting green light, the red pulse goes to the red video system, and the
blue pulse goes to the blue video system. The sequence then repeats itself,
going from green, to red, to blue for as long as the equipment is in use. To
insure that the sampler tube sends the series of pulses to the various video
amplifiers in proper sequence, the trailing edge of the horizontal synchronizing
pulse is used to drive both receiver and transmitter sampler tubes.
When the three colored pulses pass through their respective video amplifier
systems, they are smoothed out to the sine wave form shown in Fig. 6B.
Note that while all of the signals are shown together in this illustration,
only the green signal goes to the green cathode-ray tube, only the red signal
goes to the red cathode-ray tube, and only the blue signal goes to the blue
cathode-ray tube. The image that is produced on each cathode-ray tube will thus
depend upon how much of the scene being sent by the transmitter contains that
particular color. If, for example, there is a considerable amount of red detail
in the scene, with little blue and say slightly more green, then the amount
of detail visible on each separate image tube will vary accordingly. The light
output of all tubes are combined then to form the complete picture, to provide
the true shading of the original scene.
In the receiver shown in Fig. 5, the total signal consisting of the
sampled signal plus the mixed-highs has been inserted in the receiver sampler
and when this unit samples portions of the incoming signal, it obtains for each
pulse the proper low frequencies for that color plus a combination of the mixed-highs.
Fig. 9. Another way of combining the three colored image tubes.
Consider carefully what happens to the high frequencies. At the transmitter
these high-frequency components of each color were combined, first with each
other, and then with the low-frequency composite signal obtained from the output
of the sampler. At the receiver, when the electronic sampler samples the signal,
it will obtain not only the particular color wanted, say blue, green, or red,
but in addition, it will also receive a combination of the high-frequency components
of all three colors at the same time. Thus, each cathode-ray tube will have
its own color plus essentially the same highs or fine detail. Since each image
tube receives the same amount of fine detail, the combination of these three
colors in the final image will produce either white, black, or intermediate
shades of grey. This is because the combination of the three primary colors,
in equal amount, will produce white or its equivalent. Thus we see that in a
"mixed-highs" system, the fine detail of the image will appear in monochrome,
and the larger detail will be in color.
The "mixed-highs" system is similar to the process of color rotogravure used
in printing newspapers and periodicals. To print a color photo, the three primary
colors are used, with the addition of a fourth plate which is black. This fourth
plate adds black, white, and the intermediate shades of grey to the image formed
by the three primary colors. It has been found that through the use of this
fourth plate, the depth, emphasis, and richness of the picture are increased.
The same results are observed in television.
Reception with Black-and-White Receivers
The signal which is radiated by the color transmitter consists of a composite
voltage obtained by combining the low-frequency components of each color with
the mixed-high components. The total signal, therefore, possesses all of the
information needed to develop a black-and-white image with full resolution.
When a black-and-white receiver is tuned to a color broadcast station, the total
signal, after the video second detector, is passed through several video amplifiers
and then applied to a conventional cathode-ray tube. It is true that there is
a 3.8 mc. sine wave superimposed on the picture signal due to the 3.8 mc. sampling
frequency at the transmitter. This will produce a dot pattern on the black-and-white
image tube in highly colored areas, but the dots are not noticeable at normal
When a color receiver is tuned to a television broadcasting station transmitting
a black-and-white signal, the picture will appear in black and white with full
resolution on the color receiver screen. The successive pulses delivered to
the three image tubes will all be of equal magnitude, and, hence, will produce
varying intensities of white - which represents a normal black-and-white picture.
Color Receivers and Color Converters
Fig. 10 - Arrangement of projection tubes and their optical system.
Fig. 11 - A television color converter constructed
by CBS. With a simple adapter built into the set, it enables a black-and-white
television receiver to pick up color broadcasts. The converter is mounted on
the front of the set so that the viewer may have either type of reception by
sliding the color attachment in front or away from screen.
A color receiver requires three image tubes plus some method of combining
their images to produce the single final color picture which is viewed by the
observer. Fig. 7 illustrates one method of combining these tubes using
cathode-ray tubes which are similar electrically to present image tubes except
that the phosphorescent screen of each is designed to produce either a red,
green, or blue image. These images are then viewed through two dichroic mirrors.
The red mirror reflects the light rays streaming from the red cathode-ray tube
screen, while permitting the green and blue rays to pass. The blue dichroic
mirror reflects the blue rays, but permits the green (and all other) rays to
pass. An observer, standing in front of the first mirror, thus sees only the
combined color pattern of all three tubes.
Another means of mounting. the three tubes, in order to obtain the final
image by reflection from a silvered mirror, is shown in Fig. 9. Again two
dichroic mirrors are required.
It is not necessary to restrict the tube arrangement to direct-viewing tubes.
Projection systems are also perfectly feasible and Figs. 8 and 10 show the manner
in which the projection beams can be combined to form the final enlarged color
image. The cabinet to house the projection tubes, Fig. 12, is very similar
to black-and-white pro-jection cabinets.
An important feature of this system is its compatibility with television
receivers already on the market. From an examination of Fig. 5 it can be
seen that to convert a current black-and-white receiver to receive color transmission
with the foregoing system requires the addition of color sampling circuits and
three color image tubes. Just how expensive something like this may be is difficult
to foretell at this time since there is a very distinct possibility that a single
cathode-ray tube using three separate guns will take the place of the three
color image tubes. Such a tube has been developed experimentally both in this
country and in England, but has never been manufactured in any quantity.
It is claimed by RCA that color transmissions can be received with a simplified
receiver using two colors instead of three. The two colors are blue-green and
green-red. A block diagram of a two-color television receiver is shown in Fig. 2.
It is seen to be similar to the diagram of Fig. 5 except that now only
two image tubes and two video amplifier systems are required. The sampling method
remains essentially the same, although the times when samples are taken of the
composite wave is altered.
In Fig. 4, the sine waves due to each of the color pulses are shown
separately, together with the composite signal. At time 1, the green sine wave
is at a maximum and the other two color signals are passing through zero. Hence,
if the receiver sampler takes a sample of the composite wave at this instant,
it will obtain a pulse of voltage which is governed only by the green signal.
This pulse, if the system is operating properly, will go into the video amplifiers
feeding the green image tube.
Fig. 12 - Front and rear views of RCA color projection
receiver. Image is 15" x 20".
By the same reasoning, a pulse sample taken at time 2 will represent the
red signal and a pulse sample at time 3 will represent the blue signal. At time
4, the sequence starts over again.
For the two-color television receiver, the same signals as in Fig. 4
are shown in Fig. 13; however, the instants when samples are taken have
now been altered. The composite signal is sampled for blue-green at a time when
both blue and green are in a positive direction. This is indicated by the line
marked B-G. Similarly, the composite signal is sampled for green-red at a time
when both of these components are in a positive direction. This is indicated
by the line marked G-R. No sample is taken at the third point.
The two samples are fed to separate video amplifiers and cathode-ray tubes
and the final image is formed by combining the light output of both screens.
A color converter using a two-color picture-reproducing system is shown in Fig. 14.
To keep the cost of this color converter as low as possible, the black-and-white
image tube already in the receiver is used with a suitable filter placed in
front of it. All we require then is a sampling circuit and a second image tube
and a suitable dichroic mirror. If the two-color system is to be used for an
inexpensive color television receiver, the two image tubes would possess the
proper color phosphors and filters would not be needed.
The CBS System
The CBS color system has been labeled by many as a "mechanical" system but
CBS claims this is not actually so. True, up to now, in nearly all tests run
with the equipment, mechanical scanning filters have been used - but the mechanical
components could be replaced by electronic methods both at the transmitter and
Fig. 14 - Two-color picture-reproducing system.
At the studio camera, a rotating color disc is placed in front of an Image
Orthicon camera tube. See Fig. 15. The color disc contains the three primary
filters, red, blue, and green arranged so that there are four groups of these
three primary colors, or a total of 12 filter segments. The light from the televised
scene must pass through one of these filter segments to reach the camera tube
and in so doing loses all color components except the one which matches the
color of the filter. The speed of the disc is synchronized with the action of
the electron beam within the camera tube so that one field is scanned while
a filter segment is passing in front of the camera tube.
Fig. 13 - Operation of the receiver sampler in a two-color
To illustrate, suppose that at any one instant the red filter is in front
of the camera tube. During this time, the red filter is permitting only light
from the red-colored sections of the scene to reach the mosaic of the tube.
With the red filter in position, the electron beam scans the mosaic and the
electrical pulses corresponding to the red-colored sections of the scene are
formed and transmitted through the video amplifiers. The filter in front of
the camera tube remains in this position throughout the entire scanning run
(one field of either the odd or even lines) of the electron beam. The same sequence
is followed as each of the other filters moves in front of the camera tube.
The electrical pulses from each of these scannings follow each other in succession
through the various transmitter amplifiers.
At the receiver (Fig. 16) the pulses arrive in the same order in which
they were transmitted. As they are traced out on an ordinary cathode-ray tube
screen, the corresponding colored filter should be in position in front of the
viewing screen. The observer, in viewing the image through the rotating filter,
sees these colors as they appeared when they entered the camera tube. The lines
are traced so rapidly that each individual color sequence blends into the next,
and only the completed image appears to be present. This is similar to the action
with ordinary television images. Here, too, the even and odd lines are scanned
separately, but the observer integrates them both in his mind to form the resultant
Fig. 15 - In the CBS color system, the incoming light
rays are filtered by a color disc before reaching the camera tube.
Fig. 16 - Block diagram of CBS color unit.
To insure that the color disc at the receiver is in step with the color disc
at the transmitter, a special synchronizing pulse is incorporated into the video
It is possible to replace the rotating color disc and the single black-and-white
cathode-ray tube at the receiver by an all electronic viewing system consisting
of three separately colored image tubes. The incoming signals would then be
routed by a special cir-cuit to the proper image tube and the final image would
be formed by superimposing the light output of each tube. This is similar to
the RCA system. It is, however, admittedly more economical to utilize the mechanical
The CBS color system, as currently constituted, occupies a 4.5 mc. bandwidth,
uses 405 lines (as against 525 lines in the present black-and-white system),
and 144 fields per second. With these standards the number of picture elements
along each line is 45% less than in standard black-and-white pictures. CBS claims
that with normal program material, the loss in detail is not too noticeable.
Thus, we have here the two major systems competing with each other before
the FCC. The RCA system is essentially a dot sequential system while the CBS
is field sequential. Demonstrations are being conducted by both organizations
(along with others) at the hearings with the avowed purpose of attempting to
bring to a head the controversy and possibly enable the FCC to come to a definite
conclusion concerning the feasibility of either system (or possibly some other
system, of which several have been advanced) and establish a set of standards.
It is even possible that the FCC will feel that none of the systems thus far
advanced are suitable and refrain from making any decision at this time, preferring
to delay the introduction of color television until more experimental data is
available. In any event, the choice, or lack of it, is expected to be definitely
announced within the next few months.
Color Television Articles
Posted January 6, 2017