ABSTRACT
This chapter reviews a multi-toning blue-noise model proposed by J. Bacca Rodriguez intended to serve as a standard by which multi-tone conversion algorithms are optimized, with the better of two algorithms being the one whose spectral features more closely match those of the proposed model. It discusses a set of algorithms, introduced by Bacca, that combine threshold decomposition with well-known blue-noise halftoning algorithms to generate multi-tone dither patters that show the optimal spectral characteristics. The chapter looks at the extension of error-diffusion and of direct binary search to multi-toning. The characterization of the spectral profile of blue-noise multi-tones needs to take into account all these components and evaluate their interaction. The optimal multi-tone dither pattern will, therefore, be the one that, after filtered with a human visual system model filter, contains the least amount of remanent quantization noise. The observations provide a strong motivation to incorporate the correlation between different inks into the analysis and synthesis of multi-tones.
