Patent ID: 7948659

Claim:
A halftoning device that converts an input pixel signal of 8 bits per pixel into an output pixel signal of r bits per pixel, wherein r is less than 8, the halftoning device comprising: a threshold value array storage that stores a threshold value array comprising a threshold value of 8 bits ranging from 0 to 255, where a memory area of 8 bits depth is used: a threshold value expansion unit that expands the threshold value of 8 bits to an expanded threshold value of n bits per pixel by multiplying higher-order (8-s) bits of the threshold value by a scaling factor Np while maintaining lower-order s bits of the threshold value; and a gradation correction unit that expands the input pixel signal into an expanded pixel signal of n bits per pixel, wherein n is greater than 8 and that matches a range of an output value with a range of the expanded threshold value, wherein s is an integer, wherein Δn is a difference value between the expanded pixel signal and the expanded threshold value corresponding to the threshold value that is selected for each input pixel signal, wherein Δh′ varies in relation to a value of s, and wherein: when Δn<0 is satisfied, all bits of the output pixel signal are set to 0, when Δn>Δh′ is satisfied, all bits of the output pixel signal are set to 1, and in other cases, the output pixel signal is set to higher-order r bits of the difference value Δn while omitting lower-order s bits.