Among the various digital haiftoning methods, carrier procedures have the advantage of being fast and requiring few computational resources. However, because they are pixel-oriented a!- gorithms, they offer!ess flexibility than more complex algorithms that involve the information from a neighborhood or the entire image in the quantization of each pixel. By introducing noninteger ratios between the carrier and raster period, the carrier procedure can be
adapted to the spectral characteristics of the visual system. The spectral noise distribution can be optimized in this regard for twodimensional,
periodic carriers with arbitrary shape.