A device that receives a television signal and effects the sound and vision reproduction of the original scene. A traditional television receiver contains the following: detecting and amplifying circuits that extract the video and audio signals from the received signal; circuits that extract the synchronizing signals from the received signal and control the appearance of the image; a picture tube that reproduces the picture, and audio circuits that reproduce the transmitted sound. A desired broadcast channel may be selected using a tuner. A colour television receiver also contains extra decoding circuits that extract the chrominance (colour) information from the received signal (see colour picture tube). In digital television systems, the video information has been encoded into digital form at the transmitter and must be decoded at the receiver (see digital codes). Television receivers using cathode-ray tubes have now been largely replaced by those using LCDs or plasma displays (see flatscreen display).

Various control circuits are provided in order to compensate for minor variations in the received signal level.

• • automatic brightness control is used to maintain automatically a constant value for the average luminance (brightness) level of the image;

• • automatic contrast control maintains a constant value between the black peak and the white peak of the image despite input variations.

Various manual controls are also usually available:

• • horizontal hold and vertical hold are controls that adjust the starting points of the line sweep and field scan, respectively, relative to the television screen;

• • brightness and contrast controls adjust the average brightness and contrast of the image. They adjust the average luminance level and contrast range between the black and white peaks, respectively;

• • colour saturation control and tint control are provided in colour television receivers. The colour saturation alters the total intensity of all three electrons beams and makes the final image more coloured or less coloured. The tint control alters the relative intensities of the three electron beams to adjust the colour balance of the picture.