FM screening by the local exhaustive search, with hardware acceleration

Summary form only given. The main contribution of this paper is to show a new approach for FM screening which we call local exhaustive search (LES) method, and to present ways to accelerate the computation using an FPGA. FM screening, as opposed to conventional AM screening, keeps unit dot size when converting an original gray-scale image into the binary image for printing. FM screening pays great attention to generate moire-free binary images reproducing continuous-tone and fine details of original photographic images. Our basic approach for FM screening is to generate a binary image whose projected image onto human eyes is very close to the original image. The projected image is computed by applying a Gaussian filter to the binary image. LES performs an exhaustive search for each of the small square subimages in the binary image and replaces the subimage by the best binary pattern. The exhaustive search is repeated until no more improvement is possible. The experimental results show that LES produces high quality sharp binary images. We also implemented LES on an FPGA to accelerate the computation and achieved a speedup factor of up to 43 over the software implementations.