Apparatus and method for generating a dispersed dot half tone picture from a continuous tone picture.

摘要

Apparatus and method for generating a dispersed dot half tone picture from a continuous tone picture involves the making of a thresholding decision at each picture element to decide whether or not a dot is printed in the output picture and is characterised in that cumulative weighted sums of the errors between the original continuous tone picture and the output half tone picture at each picture element are held for each column of the picture matrix and from these column sums of errors a sector sum of errors is formed and used in the thresholding decision. The column and sector sums of errors are up-dated by simple recursive relationships. Edge enhancement is introduced in a simple manner obviating the need to calculate a local greyscale average. Distracting patterns of dots in the output picture are broken up by the use of carefully selected threshold values.