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

2. 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]

3. 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

4. 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

5. 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

6. 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