| 摘要 |
PROBLEM TO BE SOLVED: To obtain a multi-gradation image with higher image quality in which a noise amount in a highlight part is small without losing a detailed edge or the like. SOLUTION: Eight area patterns are stored in 1st area pattern setting circuit 601-8th area pattern setting circuit 608, and arithmetic circuits 609-616 at a next stage calculate black pixel number N1 -N8 included in a corresponding area pattern. Then the arithmetic circuits 609-616 obtain a maximum value and a minimum value among measured black pixel numbers N1 -N8 and a high frequency edge is detected by comparing the difference with a preset threshold level Tg1. A 2nd edge detection circuit 502 detects a low frequency edge similarly and signal values S1 , S2 denoting the result of detection of each edge detection circuit are given to a multilevel conversion value selection circuit 11, in which the multilevel conversion system in response to the signals S1 , S2 is selected. |
