Error-Diffusion Robust to Mis-Registration in Multi-Pass Printing

Error-diffusion and its variants are commonly used halftoning techniques that produce dispersed dot (FM) halftones, which are often preferred because they are free from low-frequency structure. Since the isolated dots resulting from error diffusion are reproduced well on inkjet printers, error diffusion is commonly employed in these devices. Inkjet printers often print a page in two passes in order to allow for better drying of inks and to minimize appearance of a head signature. Any potential misregistration between the passes is typically not comprehended in the error-diffusion halftoning process. The mis-registration between the passes can therefore cause significantly increased graininess (low-frequency structure) in printed error diffusion images even though the electronic bitmaps generated by error diffusion are free from low-frequency structure. In this paper, we propose modifications to the error-diffusion halftoning process that take the two pass printing into account and produce halftones that are robust to inter-pass mis-registration errors. This allows reduced tolerances and alignment requirements in manufacturing that translate to lower cost. The proposed technique works by suitably biasing the error diffusion process to ensure that a majority of the minority pixels are concentrated in a single pass, which provides improved robustness to mis-registration between the passes. Experimental results demonstrate that the modified error-diffusion technique performs significantly better than regular error diffusion in the presence of mis-registration errors.