Method and system of processing image signals

摘要

In an image area measuring apparatus of the type wherein an image bearing surface of a lithographic printing plate is photographed with a television camera to produce an image signal, the image signal is converted into a digital signal to obtain a measured value and an image area of each one of a plurality of zones of the image bearing surface is determined by an arithmetic operation utilizing the measured value, the image signal is judged by the step of judging the image signal by taking the percentage of dot ratio of a predetermined constant value as a 100% dot ratio when the image bearing surface does not contain a portion corresponding to 100% dot ratio. Further the image signal is proofed by a method including the steps of obtaining a proof value corresponding to the measured value from a compensation table utilizing logarithmic functions by using a proof plate having a uniform light reflective index, determining a proof value for the measured value of the lithographic printing plate from the proof table, determining a difference between the proof value and the compensation value, and determining the image area from the difference.