A method and apparatus for transferring an image of predetermined length onto a substrate by selective energization of a row of printing elements in a printhead of a printing apparatus. The printing apparatus may be arranged with a print ribbon located between the printhead and the substrate such that ink is selectively transferred from the ribbon to the substrate as a result of energizations of the printing elements. The image to be printed is rendered in memory as a series of rows of pixels and the apparatus is set up to download the rendered rows of pixels to the printhead successively. The relative positioning of successively printed rows of pixels on the substrate is determined by relative displacement between the printhead and the substrate. The apparatus is set up to control the positioning of the rows of pixels by controlling the delay between successive energizations of the printing elements. Operational characteristics of the printing apparatus are determined, and the image is rendered such that the number of rows of the pixels in the rendered image is no greater than the maximum number of rows of pixels which can be printed in the length of the image given the operational characteristics of the printing apparatus. Additional rows of pixels may be printed between pairs of rows of printed which correspond to consecutive rows in the rendered image. The pixel content of each additional row is a function of the pixel content of the adjacent pairs of rows.
1. A method for generating a printed image by printing or not printing a pixel of the image in each of a matrix of rows and columns of pixel areas, wherein alternate rows of the image are printed so as to produce spaced rows of pixels on the basis of stored pixel data read from an image memory, and intervening rows of the image are printed on the basis of calculated pixel data, the calculated pixel data for any one pixel area being calculated as a function of the stored pixel data related to adjacent pixel areas in the two rows adjacent to the row of the said one pixel area.
2. An apparatus for generating a printed image, comprising a memory for storing pixel data corresponding to rows of pixels in an image to be printed, means for printing out the stored pixel data so as to produce spaced rows of pixels with each row of pixels in the printed image corresponding to a row of the stored pixel data, and means for printing out additional rows of pixel data between each pair of rows of pixel data which correspond to adjacent rows of pixel data in the stored image, the additional rows of pixel data being printed on the basis of the calculation of pixel data from the stored pixel data related to the two adjacent rows of pixels.