Frequency Modulated Halftoning and Dot Gain

A printed image often appears darker than the original due to physical and optical dot gain. Normally, the original is compensated for dot gain prior to halftoning using either an experimental dot gain curve or a dot gain model. Because of the nonlinearity of dot-gain with respect to the nominal dot percentage, the compensation may cause loss of details in the halftoned image, affecting the print quality negatively. In this presentation, we make comparisons between three dot-gain models, the Yule-Nielsen, dot overlap, and the unified dot-gain model proposed very recently. The impact of dot-gain compensation on halftoning is also studied by comparing two types of halftoning methods, the ordinary Error Diffusion and the dot-location-optimization method with consideration of edge enhancement. Applications show that the latter provides us with a fairly good tone reproduction while preserving the details.