A DVD image represents standard definition. This happens so quickly that our eyes blend the 60 still fields together into 30 frames (each frame is a still picture) and we see only continuous motion.īecause the image is composed of 480 interlaced lines, the system is called 480i, and is known as standard definition in the world of digital TV. A single frame of TV is composed of two "fields" of 240 lines each, presented every 1/60 of a second, which are " interlaced " or interwoven to form a full picture every 1/30 second. The 60-year-old analog TV system all of us grew up watching is based on 525 horizontal scanning lines, although only 480 lines are actually used to scan the picture from top to bottom across the TV screen every 1/30 of a second.
Our eyes and brain blend the rapidly changing still images into continuous and smooth action, through a process called "persistence of vision." If we sit far enough away from the TV screen, the individual clusters of colored dots blend together to form a smooth and coherent color picture that changes 30 times every second. These pulses perfectly track the signals broadcast by the television station or cable system that routes the TV signals into your home. In the case of a conventional television display, the groups of dots glow in varying degrees of brightness and hues, triggered by electrical pulses from the TV set's electronics.
What are you really looking at when you gaze at a color TV screen or a newspaper photo? On a TV screen or in a newspaper or a magazine picture, or even the computer monitor screen on which you read this text, the images are formed by groups of red, green and blue dots or "pixels" (short for picture elements).
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