A block error is a common type of error in certain types of digital television transmission, particularly those that use image compression. Its presence in a television image is a telltale sign that 1) the signal is broadcast digitally, as this type of error can not occur in analog transmission, and 2) that there is a significant amount of noise, as digital television is designed to tolerate a certain amount of interference. Block errors are usually detected, but not corrected, by the receiving device and are commonly displayed as empty black boxes in the television image.
Because of how television images are usually compressed, a block error in a single frame often results in black boxes in several subsequent frames. In the worst case, a few block errors per frame could render the video from a television broadcast unviewable.
Block errors are most common in digital satellite television, where bad weather or motion of the satellite dish can cause interference outside the broadcaster's control.
Block errors can occur at levels of interference where an analog transmission would be fuzzy but still viewable. Thus, block errors are a fine example of the consequences of trade offs in engineering. Although in ideal conditions, digital transmission far exceeds analog transmission in performance, below a certain threshold of signal to noise ratio, digital transmission becomes untenable.
Famous quotes containing the words block and/or error:
“The chess pieces are the block alphabet which shapes thoughts; and these thoughts, although making a visual design on the chess-board, express their beauty abstractly, like a poem.... I have come to the personal conclusion that while all artists are not chess players, all chess players are artists.”
—Marcel Duchamp (1887–1968)
“There exists a black kingdom which the eyes of man avoid because its landscape fails signally to flatter them. This darkness, which he imagines he can dispense with in describing the light, is error with its unknown characteristics.... Error is certainty’s constant companion. Error is the corollary of evidence. And anything said about truth may equally well be said about error: the delusion will be no greater.”
—Louis Aragon (1897–1982)