Halftone image gradation data converted to bit-train data with data retained after thresholding converted to pulse-train data

摘要

In an image recording apparatus capable of recording a halftone image, a gradation to bit-train converting table converts gradation data representing a gradation of tone at a picture element of an image into bit-train data whose bit pattern is based on the gradation data. For the gradation data representing a gradation in excess of a threshold gradation, the table converts the gradation data into such bit- train data that bits of the bit-train data corresponding to the gradation data are intermittently omitted after a train of bits corresponding to the threshold gradation is outputted. A bit-train to pulse-train converting section converts the bit-train derived from the gradiation to bit-train converting table into pulse-train signal of a pulse pattern analogous to that of the bit-train data. The pulse signal of such a discontinuous pulse pattern is applied to a heating element of a thermal head, which is provided corresponding to the picture element whose gradation data is under process. A heating temperature of the heating element is controlled below a predetermined temperature.