Print Inverse Halftoning and Its Quality Assessment Techniques

Abstract

The technology of converting halftone image back to the continuous tone image (i.e. inverse halftoning) and method of quality assessment of inverse halftone images are studied. A general method for inverse halftoning of printed image is present in the paper. We use several filters to obtain the smoothing image and edge information of halftone image, and obtain the inverse halftone result by adding the edge information on the smoothing image. The inverse halftone results using the method presented in this paper are visually better than that of using Gaussian low pass filter or that of combining Gaussian low pass filter and median filter. The PSNR of inverse halftone result of amplitude modulation image (value 18.6134) is lower than that of other halftone images, but in fact, the inverse halftone result of amplitude modulation image is visually better. While using the new index of quality assessment D presented in this paper, D value of inverse halftone result of amplitude modulation image is significantly smaller than that of frequency modulation image (the former 5.9506, the latter 0.248), which means the tone feature of inverse halftone result of the amplitude modulation image is more consistent with the continuous image. The inverse halftone results by using the method presented in this paper is good, and the method can be applied to different types of halftone images. And, the index of quality assessment D presented in this paper is helpful to avoiding wrong judgment while PSNR is not consistent with the visual result.