| 摘要 |
PURPOSE:To greatly shorten a treatment time for picture signals in controlling picture quality and improve a hitting rate of automatic control of an electronic optical system with upgraded picture quality evaluating data by using filtering treatment for collecting picture signals as required in minimum and for reducing noise. CONSTITUTION:A CPU 11 varies the current values of an electromagnetic lens 2 while scanning an electron beam 1, at this time memorizes detection signals from a sample 3 as picture data in a memory 11b until the number of frames to allow for filtering treatment is reached, and performs same-scanning-position weighted computation of the picture data located at the same scanning position of frames noteworthy through the memory 11b and frames before and behind them. Next, a picture quality evaluation of the electromagnetic lens in steps varied in accordance with the picture data is found so that the electromagnetic lens can automatically be controlled to obtain adequate picture data from the evaluation. |
