| 摘要 |
PURPOSE:To improve the reproducibility of an edge part by detecting variation in the internal density of each picture element by a Laplacean filter and detecting a density inclination direction by using plural density gradient detection filters. CONSTITUTION:A many-gradation image signal is inputted to an edge part detecting circuit 3. The edge part detecting circuit 3 performs Laplacian or the like spatial filter calculating and sends information regarding whether or not an input picture element is at an edge part to a density gradient direction detection circuit 4 and a multivalued pattern table 2. When it is decided that the picture element is at the edge part, the density gradient direction detecting circuit 4 with a spatial filter function calculates the density gradient direction of a target picture element and sends gradient direction information to the multivalued pattern table 2. Pattern information to be recorded which is obtained from the multivalued pattern table 2 and power-feeding energy information are supplied to a thermal recording circuit 6 to determine the power feeding pulse width of each heating element of a thermal head. Consequently, the reproducibility of an edge part having abrupt variation in density is improved.
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