Tadahiko Kimoto
Digital halftone, improved gray-scale quantization, error diffusion, Hilbert scan, subjective testing
This paper focuses on multi-level halftoning by using the improved gray-scale (IGS) quantization for digital gray-scale images. The objective is to present a scheme to implement the IGS halftoning in a manner such that the resulting image achieves halftone quality comparable to that given by error diffusion halftoning. By analyzing the quantizing formula, the properties of IGS halftoning are revealed and it is proven that the DC component of a source image can be conserved through halftoning. Then, a complete procedure to carry out the IGS halftoning on a source image with achieving the DC conservation is defined on the basis of the analyses. From the results of experiment conducted on test gray-scale images, the performance of the random variable used for IGS halftoning is evaluated and then, the extent of randomness of the quantizing process is demonstrated. Also, halftone quality of the resulting images is evaluated from the measurements by subjective evaluations of human observers. As a result, for 3 or more-bit, or 8 or more-level multi-level halftoning, the IGS halftoning is available instead of the error diffusion halftoning.
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