Halftoning is a process of transforming a gray scale image to a halftone (only black
and white). It creates the illusion of gray-scale by varying the average dot density in
local regions of images. Halftoning takes the advantage of the fact that eyes integrate
intensity of small image regions as in Fig.1.6. However, spatial resolution must be
sacrificed (output image will be larger than the original), which refers to image
itself based on direct manipulation pixels, for gray-scale resolution unless the output
device can be over-sampled as most ink-jet printers.