| 摘要 |
PROBLEM TO BE SOLVED: To provide a thermal printer capable of printing in a desired density from a portion just rear a portion where a gradation value is changed even when the gradation value is suddenly changed in the sub-scanning direction. SOLUTION: Line image data S40 of input image data Si is outputted from a frame memory 40. The line image data S40 is inputted to line memories 51a, 51b. Gradation values of current line image data S51a and previous line image data S51b are converted to current pulse width data S52a and previous pulse width data S52b, then a difference value S53 is calculated by a subtracting section 53. The difference value S53 is converted to an adding value S54 and a history value S58 is added to the adding value S54, then a history value S55 is outputted. The history value S55 is attenuated to be stored in a history value memory 58 and the history value S58 is applied to an adding section 55. The history value S55 is converted to a coefficient S56 and the current pulse width data S52a is multiplied to the coefficient S56, then pulse width data S50 is outputted. The pulse width data S50 is inputted to a thermal head section 60.
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