yiq

YIQ is a color space used in analog television broadcasting, particularly in the NTSC (National Television System Committee) standard. It is a transformation of the RGB (red, green, blue) color model designed to encode color information in a way that is compatible with monochrome television receivers and to optimize for human visual perception. The YIQ color space separates the luminance (brightness) information from the chrominance (color) information.

The 'Y' component represents the luminance, which is a weighted sum of the red, green, and blue components of an image. This 'Y' signal is what a black-and-white television can display. The 'I' and 'Q' components, together, represent the chrominance. The 'I' component carries information about the orange-to-cyan hues, while the 'Q' component carries information about the purple-to-green hues. The amplitudes of the I and Q signals correspond to the saturation of the color, and their phase corresponds to the hue.

The YIQ color space was developed to allow for backward compatibility with existing monochrome television sets. By transmitting the luminance signal separately, color broadcasts could still be viewed in black and white. The chrominance information was transmitted in a bandwidth-limited manner, exploiting the fact that the human eye is less sensitive to color detail than to brightness detail. This allowed for efficient encoding of color information without significantly increasing the bandwidth required for the broadcast signal. While YIQ was crucial for analog NTSC television, modern digital television systems typically use color spaces like YCbCr.