APPARATUS FOR TESTING IN RAPID SUCCESSION EACH OF A MULTIPLICITY OF SHEETS IN A SEPARATE OF CONTINUOUS FORM

摘要

A method of inspecting a pixel for tolerable variation from a corresponding selected pixel in a master image comprises establishing a data word of which the bits each indicate whether or not all the master image pixels in the neighbourhood of the selected pixel all have values (i.e. brightness values) within a respective range. A data representing the value of the inspected pixel is compared simultaneously with the ranges of values asssociated with the bits of the data word, which provides gating for the comparisons.