JPS57119564A - Half-tone picture processing method - Google Patents

Abstract

PURPOSE:To obtain an output picture from which moire and granular noise are removed by setting up more than one threshold matrix by selecting one of the threshold matrixes for more than one picture elements of a half-tone picture at random, and by comparing it with the picture elements of the half-tone picture. CONSTITUTION:An analog density signal of a picture is inputted to an A/D converter 100 is sampled and quantized, synchronizing with clock pulses from a clock circuit 102, by picture elements to input the result to a comparing circuit 104. A counter 106 counts the clock pulses from the circuit 102, and a random-number generator is triggers for every four picture elements in the main scanning direction of a half-tone picture and for every four lines in the subordinate scanning direction to generate random number. In a table 110, four threshold matrixes are stored, and the threshold-value matrix specified by the random number is read out of the table 110 and registered in a buffer 112. The circuit 104 compares a picture-element density signal with the corresponding threshold value of the threshold-value matrix from the buffer 112, thereby outputting a picture-element signal ''1'' (black) when the density level is higher or ''0'' (white) when lower.