When television was initially established, it could only handle black-and-white images; engineers battled to figure out how to deal with color, which was a considerably more complicated challenge. According to light science, any hue may be created by blending a combination of the three fundamental colors: red, green, and blue. For example, yellow can be produced by mixing equal amounts of red and green. Television uses similar technology, but instead of using actual colors, it creates these effects by varying the intensity of each primary color behind the screen.
Television's original design had black bars at the top and bottom of each image to indicate where one picture ended and another began. However, this proved difficult when showing movies, so the black bar system was replaced with a simple horizontal line that could be placed anywhere within the image. This allowed the viewer to know without having to watch the screen what part of the movie was being shown.
The choice of these two systems caused considerable controversy when they were first proposed. Some believed the use of bars would be easier for viewers to understand, while others feared it would cause confusion if not done properly. In fact, before either system was adopted, several other proposals were made, such as putting colored dots on the screen to represent each frame or placing four small squares in a corner of the image to show where one picture ends and another begins.
Eventually, both systems were accepted and have been used ever since.
As a result, just three hues (red, green, and blue) are required in color television to generate a full spectrum of colors in a color TV image. In essence, the color TV process is built on separating (in the camera) and then merging varying quantities of red, green, and blue.
When you look at a color photograph or color film, you are seeing three separate images, one for each color channel: red, green, and blue. When these three images are viewed together, the entire range of colors can be displayed.
In a black-and-white photograph or video, only two colors are used: white (or light gray) for shadows, and black for lights. Because dark areas contain only white or black, they appear single colored in a black-and-white image.
Color photography is becoming more common today, but it uses three types of photos to create a color picture: red, green, and blue. The camera mixes the colors from these photos together to reproduce the whole spectrum of colors found in reality.
The need for only three colors instead of the full range of colors that exist in nature makes color photography and television as we know them today easier and cheaper to produce.
Black-and-white photographs use only white and black pixels to display all shades of gray.
It may be evident at this point that any hue of the rainbow may be generated by mixing the right proportion of red, green, and blue light. However, it is also possible to generate other colors using more than three hues. For example, yellow can be generated from a combination of red, green, and blue lights, while white can be generated from a mixture of all the colors of the spectrum.
The number of colors available from a tri-chromatic system is limited to 216 = 65 592. Additional colors can be obtained by adding monochromes (single wavelengths) or polychromes (combinations of wavelengths). A monochrome adds only one color to the mix, so a cyan ray (from the color wheel) would not be mixed with any other color to produce gray, it would simply replace blue as the color generating element. Polychromes are useful for producing "fuzzy" colors, such as pink or purple. These colors cannot be produced with tri-chromatics alone because the ratio of red:green:blue is always fixed. However, with polychromics it's possible to vary the amount of each color present in the mix.