US Patent 7787002 Digital writing apparatus

In transfer of even pixel data, focusing on even-number data, only the even data is selected out of eight pixels of image data read out from a storage circuit and transferred to an LED head in a unit of four bits. Four pixel data are simply selected out of eight pixels without performing one-pixel conversion. In transfer of odd pixel data, focusing on odd data, when data is “0”, “0” is directly transferred. When data is “1”, if the previous pixel data is “1”, “1” is directly transferred, and if the previous pixel data is “0”, data is converted into “0” to be transferred.