Improved Multi-level Screening with MJBNM for Smooth Tone Transition

This paper proposes a multitoning method based on threshold modulation using a Modified Jointly Blue Noise Mask (MJBNM) to reduce banding artifacts. Since banding artifacts appear as uniform dot distributions around the intermediate output levels, such halftone patterns result in discontinuity and a visually unpleasing output in smooth transition regions. Therefore, to reduce these banding artifacts, the principal cause of banding artifacts is first analyzed. Based on the analytical results, the proposed method then arranges the dot distribution by introducing pixels to the neighborhood of the output levels through threshold modulation using an MJBNM, which takes into account the chrominance error and correlation between channels. Depending on the input value, the original threshold range of the MJBNM is first scaled linearly so that the minimum and maximum of the scaled range include some more pixels than the adjacent two output levels containing the input value. If an input pixel is inside the vicinity of any intermediate output level producing banding artifacts, the output is set to one of those output levels based on comparing the result to scaled threshold values and a threshold modulation parameter that determines the dot density. Otherwise, a conventional multitoning method is applied. As a result, the proposed method effectively decreases the appearance of banding artifacts around the intermediate output levels.