The term “television” literally means “vision at a distance.” A television screen serves as a “window” through which a viewer can observe events happening far away. However, television engineers and broadcasters are essentially in the business of creating illusions. What appears on a television screen is a constantly changing pattern of light generated by a tiny flying spot. This pattern, when projected on the screen, stimulates the viewer’s eye and nervous system in such a way that they perceive the illusion of witnessing a real scene unfolding before the camera. Naturally, the goal is to make this illusion as convincing as possible, reducing the strain on the viewer’s imagination.
Color television is more captivating than black-and-white television because it creates more realistic illusions. For most people, normal vision includes color, and any image-producing process that lacks color demands more from the viewer’s imagination. Although black-and-white images, such as green grass or blue skies, can still convey meaning and perception, they are far more effective when presented in full color. Outdoor scenes, in particular, may seem uninteresting in black-and-white but come alive in color, offering a much richer aesthetic experience.
When developing a color television system for broadcasting, it becomes clear that the challenge goes beyond purely technical factors. Any color television system must meet several essential criteria: technical requirements (Does it produce high-quality images?), compliance with government regulations (Does it meet FCC standards?), economic feasibility (Can receivers be mass-produced, and does the system allow for affordable color broadcasting?), public interest (Does it enhance, rather than detract from, existing broadcast services?), and efficient use of resources (Does it make optimal use of the frequency spectrum?).
After considering these various factors, a set of minimum requirements for a broadcast color television system can be established. These criteria, widely supported by engineers in the industry, include:
- Colorimetric Requirement: The system should produce high-quality images with accurate color reproduction. It must also meet performance standards for flicker, brightness, contrast, resolution, and picture texture, comparable to existing black-and-white systems.
- Compatibility Requirement: The color television system should be compatible with existing black-and-white receivers, allowing them to produce clear images from color broadcasts without needing modifications. Conversely, color receivers should still be able to display black-and-white images from monochrome signals.
- Channel Utilization Requirement: The system must operate within a 6-megacycle broadcast channel, in accordance with FCC regulations. Additionally, it should make the best possible use of the available frequency spectrum by allocating space for different components of the color signal based on how the human eye processes the information.
In 1949, the Radio Corporation of America (RCA) introduced a color television system that met the basic criteria for a broadcast service. Since 1950, RCA engineers have worked alongside engineers from various companies through the National Television System Committee (NTSC) to refine the signal specifications for optimal performance within the framework of the original RCA system. These specifications were submitted to the FCC on July 23, 1953, and were approved on December 17, 1953. This paper explains the operational principles of the RCA color system and provides details about the FCC-approved signal specifications, which ensure that the system meets the previously established requirements.
Basic Colorimetric Principles
For most people, color vision is governed by three key attributes: brightness, hue, and saturation. Brightness refers to how light or dark a color appears, ranging from black (the absence of light) to pure white. Hue is the color itself—red, green, yellow, blue, and so on. Saturation describes the intensity of a color; highly saturated colors are vivid and intense, while less saturated colors are pale or pastel.
One of the main challenges in converting a monochrome television system to color is managing these additional attributes. Unlike black-and-white systems, which only control brightness, color television must handle three independent variables: brightness, hue, and saturation. To achieve this, the system requires at least three separate signals, each representing one of these components. These signals must be compatible with the physical limitations of both the pickup tubes and the display devices. By considering the relationship between light energy and color perception, the RCA color system ensures that these requirements are met in a practical and effective way.