Halftone postprocessing for improved highlight rendition

Many halftoning algorithms tend to render highlight regions with objectionable dot distributions. To alleviate this artifact, we introduce a halftone postprocessing algorithm called the Springs algorithm. The objective of Springs is to rearrange dots in affected regions for a smoother more attractive rendition. We describe the Springs algorithm, and we show results which demonstrate its effectiveness. The heart of this algorithm is a simple dot-rearrangement heuristic which results in a more isotropic dot distribution. The approach is to treat any well-isolated dot as if it were connected to neighboring dots by springs, and to move it to a location where the energy in the springs is a minimum. Applied to the whole image, this could degrade the halftone appearance. However, Springs only moves dots in selected regions of the image. To select these regions, Springs employs a segmentation scheme which is based on finding light regions which do not exhibit strong edge structures