Abstract: In a one-pass multi-head type thermal printer, a slack portion is provided in a recording sheet on each transport path from one thermal head to another. The slack portion is provided by a difference in transporting speed between adjacent two transport members, or by guiding the leading end of the recording sheet along a concavely curved guide member between the adjacent two thermal heads. A change in transporting speed caused by a change in load to the recording sheet during transportation is absorbed in the slack portion, and does not have bad influence on recording.

Abstract: Half-tone image data and character image data are discriminated from each other with reference to discrimination data, and are stored separately from each other. In accordance with the image to be printed, one of a character print table and a half-tone print table is selected. In accordance with the result of comparison of the character image data with comparison data read from the character print table, characters are recorded using two kinds of character dot print patterns for recording a dot in the whole area of an associated pixel and for recording no dot. Half-tone images are recorded in the area gradation method using half-tone dot print patterns in accordance with the result of comparison of the half-tone image data with comparison data read from the half-tone print table. One pixel is divided into a plurality of sub-lines. The recording of the characters is performed at intervals of N sub-lines, N is an integer. The recording of the half-tone images is performed at intervals of one sub-line.

Abstract: A thermal recording method and device for recording a half-tone image on a recording sheet, wherein each pixel includes a plurality of sub-lines, and a half-tone is produced by changing the number of the sub-lines where ink is recorded. According to a desirable tonal step, a number of drive pulses are applied to a thermal element for each pixel while the thermal element moves in a sub scan direction relative to the recording sheet, with one drive pulse corresponding to one sub-line. The width of the drive pulse corresponding to the first sub-line of each pixel is set longer than the other drive pulses for the following sub-lines, and is changed according to the pixel position in the sub scan direction. The width of the drive pulse for the first sub-line is the longest at the beginning of recording, and becomes shorter as the recording proceeds. The widths of the other drive pulses may be changed according to the sub-line position within each pixel.

Abstract: A printer has a recording head with a first plurality of recording elements being disposed in a main scan direction. The recording head records the first plurality of pixels on a recording sheet at a time. Each pixel has a second plurality of sub-lines disposed in a sub scan direction, and the number of dot-recorded sub-lines changes with tonal steps. A shift register has the first plurality.times.8-bit latches for latching sequentially inputted first plurality of image data as parallel data. The M image data are sent via a latch array to a comparator array, and set to respective the first plurality.times.8-bit magnitude comparators constituting the comparator array. A counter is incremented each time a platen drum holding a recording sheet is rotated by a one sub-line amount, and the position of each sub-line within one pixel is detected. Each 8-bit magnitude comparator maintains each recording element in a conduction enabled state until a count of the counter exceeds the contents of the image data.

Abstract: An error detection and/or correction is achieved in the horizontal direction in a block and then an error state is determined by use of an error correction in the vertical direction; furthermore, the correcting system is changed over according to the result of the determination.