| 摘要 |
An apparatus is provided for generating a random (mezzotint) screen for producing halftone copies of continuous tone documents. The random screen comprises a matrix of random numbers representing a sequence of digital reference values with respect to which video (scan) signals are compared for producing halftone picture elements (pels). The apparatus comprises a first and a second random number generator, the first being disposed for providing an initial or starting state for the second, in response to applied clock pulses. Using the supplied starting state, the second random number generator produces the random screen reference values in response to applied clock signals. The random screen reference values produced by the apparatus permits minimum halftone dot size (i.e., the size of the dot used in producing halftone images) to be varied, and halftone patterns to be selectively repeated or not repeated.
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