New results on reconstruction of continuous-tone from halftone

Two iterative methods are used to reconstruct a continuous-tone image from its halftone: successive approximation and projection onto convex sets. The halftone image is assumed to be generated by thresholding with an unknown screen function which is estimated from the halftone image in the first stage of the reconstruction process. The screen function is an integral part of both iterative reconstruction methods. The other key element is a constraint on the bandwidth of the reconstructed image. Relaxing this constraint during the course of the iterations not only reduces the RMS error after each iteration but also achieves a relatively sharp full-band reconstruction at the end