Patent ID: 7271824

Claim:
A pixel clock generating apparatus used in an optical writing system for optically producing an image at timing of a pixel clock, the pixel clock generating apparatus comprising: a data offset circuit configured to define multiple data blocks, each of the data blocks consisting of a predetermined number of successive clocks, and to produce phase data for each of the data blocks, the phase data representing an amount and a direction of phase shift made to a certain clock in each of the data blocks; and a pixel generator configured to receive the phase data from the data offset circuit and generate a phase-shifted pixel clock a predetermined number of times in each of the data blocks based on the phase data, wherein the data offset circuit comprises: a data block setting unit configured to determine said predetermined number of successive clocks in each of the data blocks, a phase data generating unit configured to produce the phase data for each of the data blocks based on said predetermined number of clocks and phase shift data, the phase shift data representing a number of times phase shift is to be carried out in each of the data blocks, and a data block setting value storage configured to store a data block setting value determined for each of the data blocks at an associated image height based on a dot offset characteristic of the optical writing system that has been measured in advance, and to read and supply the data block setting value for each of the data blocks to the data block setting unit and the phase data generating unit.