PURPOSE: To improve the size measuring accuracy of an objective pattern and the detection accuracy of pattern existence, a defect, etc., by processing picture data with uneven gradation, correcting SEM picture data including the objective pattern and removing the unevenness of gradation.

CONSTITUTION: This picture processing method is provided with the 1st step for scanning a pattern (A) to be quantized with an electronic beam 12 and obtaining the 1st picture data (B) based upon a secondary electronic signal S3, the 2nd step for executing space filtering processing by using a filter matrix at least over N times the range of one picture element in the 1st picture data and obtaining the 2nd picture data (C) and the 3rd step for adding the mean value of the gradation values of the 1st picture data to a difference between the 1st and 2nd picture data and constituted so as to obtain picture data from which the influence of background gradation is removed.