Signals are propagated to antennas. Antennas are positioned on high places, so they can easily receive signals. The purpose of the antennas is to intercept signals which are headed into space and redirect them downward to individual antennas (usually on houses). A television stations coverage area depends on several factors: 1) the capabilities of the transmitting antennas, 2) the transmitter frequency, 3) and the transmitter power. Reception of traditional broadcasting requires houses or other buildings to have antennas on top of them in order to receive signals. In order to obtain the best reception, antennas should be pointed towards transmitters. Some antennas are rotateable so they can pick up signals sent by transistors which are far away. From the antennas, the signals are sent to the receivers commonly know as television sets. Just as audio and video components were processed separately at the studio, they are processed separately in the television set. Video is processed by a cathode-ray tube called a kinescope. Inside the kinescope there are pixels that are hit by electrons. Then, an electron gun dispenses the electrons on the face of the pickup tube. This stream of electrons records an image on the inner side of the screen. The image is then recorded in lines, fields and frames. The number of lines used corresponds to the resolution quality. In the United States a 525-line resolution is the standard. In color television, three colors are picked up by the color camera: red, green and blue. The different colors portrayed in a picture are determined by how strong the colors in each pixel are. Brightness, also called luminance, also determines what a picture looks like by showing fine detail. In black and white television, the only factor that determines what a picture looks like is luminance.