Binary display of images when spot size exceeds step size

Many binary digital devices for display or printing of images are capable of placing spots of size S at an array of addressable points spaced R apart where S < R. A new representation is described for display or printing of continuous-tone images with such devices for which S/R < 2. The presentation takes into account spot overlap to assure correct tone reproduction, minimize pattern visibility, and maximize detail rendition. The algorithm is a modification of ordered dither that utilizes in one direction the subspot size addressibility of the device to increase the number of available levels of tone per unit area and enhance the good visual properties of the dither matrix. While not implementable by thresholding, the algorithm may be implemented by a nearly point-to-point spatially periodic mapping from continuous-tone image-to-device input. Fourier analysis provides a theoretical basis for the representation. Experimental work is presented that confirms the results of the analysis.