Tone Dependent Color Error Diffusion Halftoning Literature Survey Presentation Vishal Monga, March 5, 2003

Digital Halftoning: Applications and Methods Introduction Digital Halftoning: Applications and Methods Examples of reduced grayscale/color resolution Laser and inkjet printers Facsimile machines Low-cost liquid crystal displays Halftoning is wordlength reduction for images Grayscale: 8-bit to 1-bit (binary) Color: 24-bit RGB to 3-bit (1 bit per color plane) Halftoning methods Screening - pixel-parallel, fast, and simple Search based methods – Direct Binary Search(DBS) Error diffusion - 2D sigma delta modulation [Anastassiou, 1989]

Grayscale Error Diffusion Background Grayscale Error Diffusion 2- D sigma delta modulation [Anastassiou, 1989] Shape quantization noise into high frequencies Linear Gain Model [Kite, Evans, Bovik, 1997] Replace quantizer by scalar gain Ks and additive noise image + _ e(m) b(m) x(m) difference threshold compute error shape error u(m) current pixel weights Transfer functions 3/16 7/16 5/16 1/16

Direct Binary Search Used in screen design Key Paper # 1 Direct Binary Search [Analoui, Allebach 1992] Computationally too expensive for real-time applns. viz. printing Used in screen design Serves as a practical upper bound for achievable halftone quality

Tone Dependent Error Diffusion Key Paper # 2 Tone Dependent Error Diffusion b(m) + _ e(m) x(m) Tone dependent error filter Tone dependent threshold modulation Train error diffusion weights and threshold modulation [Li & Allebach, 2002] Midtone regions FFT DBS pattern for graylevel x Halftone pattern for graylevel x FFT Highlights and shadows FFT Graylevel patch x Halftone pattern for graylevel x FFT

Linear Color Vision Model Key Paper # 3 Linear Color Vision Model [Monga, Geisler, Evans, 2003] Pattern-color separable model [Poirson & Wandell, 1993] Forms the basis for Spatial CIELab [Zhang & Wandell, 1996] Best color transformation & spatial filters [Monga, Geisler, Evans, 2003] C1 C2 C3 Representation in arbitrary color space Spatial filtering