Contour is important elements of image and is usually expressed by the density jump between two areas of image. Recognition of object is usually carried out from the contour. In some cases, emerging of false contour is problem in image coding and de-cording process. Half-toning is essential processing for digital printing of continuous tone. Contour perception conditions are studied experimentally on various half-toning conditions, observation distances, and illumination conditions. It is found that the contour perception become easy as the stimulus of the halftone dot decreases in human visual system.