Inverse Halftoning Method of Error Diffused Images Using Look-Up Table with State Reduction

Various methods have been proposed for inverse halftoning (IH) of error diffusion (ED) images. Among them look-up table (LUT) method based on every possible combination of the bi-level output of reference pixels has been considered to be most effective and quite practical since IH function can be generated by simple averaging of the histogram of original con-tone levels of the target pixels in each context, and the image quality can be controlled by the number of reference pixels. In this paper, we propose a hybrid system, in which each context is composed of the combination of the conventional logic of some part of reference pixels and reduced state information given by the number of black pixels in other reference pixels. The result shows that the PSNR compared under the same number of contexts are improved from the conventional method especially when applied to the images not included in the training data