The Wavelength Dependence of the Yule-Nielsen Factor

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The Wavelength Dependence of the Yule-Nielsen
Factor

• Joseph M. Janiak and Dr. Jon Arney
• Rochester Institute of Technology

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Overview

• Background
• Experimental Design
• Results

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Optical Dot Gain

• Caused by the lateral scattering of light in a
  paper substrate.
• Another name for optical dot gain is the
  Yule-Nielsen effect.

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R F Ri (1 - F)Rp
Light Scatters in Paper
Ri and Rp are functions of F.
Light
Dot
Paper Cross Section
Paper
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R F Ri (1 - F)Rp
A special case of the Law of Conservation of
Energy.
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The Image is Darker Due to Dot Gain
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n is the Yule-Nielsen Dot Gain Parameter
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Yule-Nielsen Equation

• R Reflectance of Image
• Fo Dot Area Fraction
• Ri Reflectance of ink patch
• Rp Reflectance of paper

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What Affects n?

• Optical scattering power of paper
• Halftone pattern
• Sharpness of the edge on dots
• Opacity of the dot

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Yule-Nielsen Factor, n

• When n 1 there is no diffusion or spreading
• The theoretical limit of n is 2

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Research Objective

• Five variables were looked at to determine which
  variable was most important in controlling the
  wavelength dependence of n.

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1. Color of Ink

• Cyan
• Magenta
• Yellow

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2. Color of Paper

• Cyan
• White

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3. Paper Substrate

• Ink jet paper
• Copier paper

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Paper Substrate(cont.)

• When ink jet paper is used, ink will penetrate
  the paper less.
• Physical dot gain is reduced when inkjet paper is
  used.

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4. Opacity of Colorant

• Laser Jet 5TM printer
• Offset printer

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Opacity(cont.)

• Laser Jet 5TM uses opaque toner.
• Offset printers use transparent ink.
• Scattering within the absorbing layer should be
  more intense when opaque toner is used.

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Ink Jet/Offset vs. Laser
Ink Jet/Offset
Laser
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5. Halftone Pattern

• FM halftone
• AM halftone

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AM Halftones

• Clustered dot halftone
• Dots are printed at fixed distances from each
  other.
• Grayscale is controlled by varying size of dots.

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FM Halftones

• Error diffused halftone
• Dots are the same size throughout the halftone.
• Grayscale is controlled by varying the distance
  between the dots.

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Halftone Comparison
Clustered Dot (AM Halftone)
Error Diffused (FM Halftone)
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Halftone Sample
25 Dot Area F 0.25
Rp
Ri
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Experimental Method

• First created series of samples via computer and
  printer.
• Found sample area where dot area fraction was
  roughly 50 and took precsise measurement with
  microdensitometer.
• Found reflectances of 100 dot area region,50
  dot area region, and 0 dot area region via
  spectrophotometer.

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Experimental Method(cont.)

• Placed the known values of R,Ri,Rp, and Fo into
  Yule-Nielsen equation and solved for the value of
  n.
• Generated plots of n versus wavelength and
  absorbance spectra of samples.

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Results
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- n was larger when electrophotography was used
compared to when offset was used. - n was larger
when a clustered dot halftone was used.
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Results(cont.)
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Results(cont.)
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Results(cont.)
- again n was larger when electrophotography was
used compared to when offset was used.
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Results(cont.)
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Results Summary - Effect on n

• Color of Ink- Proved to be similar to the
  absorbance spectra. As absorbance increased, n
  increased. This is different that what has been
  seen in past research.
• Opacity- When electrophotography was used n
  values appeared to be larger.

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Results Summary - Effect on n

• Halftone-When clustered dot halftones were
  used(AM halftones) n values were larger, compared
  to when error diffused halftones were used(FM
  halftones).
• After the conclusion of this experiment it was
  seen that the Yule-Nielsen effect was not only a
  function of scattering but also absorbance.