A Simple Method to Measure MTF of Paper and its
Application for Dot Gain Analysis
Masayuki UKISHIMA, Hitomi KANEKO, Toshiya NAKAGUCH,
Norimichi TSUMURA, Markku HAUTA-KASARI*, Jussi PARKKINEN*,
and Yoichi MIYAKE
Chiba University, and University of Joensuu*
To appeare in IEICE Trans. on Fundamentals, Vol.E92-A, No.12, pp.3328-3335,
2009
Image quality of halftone print is significantly influenced by optical
characteristics of paper. Light scattering in paper produces optical dot
gain, which has a significant influence on the tone and color reproductions
of halftone print. The light scattering can be quantified by the Modulation
Transfer Function (MTF) of paper. Several methods have been proposed to
measure the MTF of paper. However, these methods have problems in efficiency
or accuracy in the measurement. In this article, a new method is proposed
to measure the MTF of paper efficiently and accurately, and the dot gain
effect on halftone print is analyzed. The MTF is calculated from the ratio
in spatial frequency domain between the responses of incident pencil light
to paper and the perfect specular reflector. Since the spatial frequency
characteristic of input pencil light can be obtained from the response
of perfect specular reflector, it does not need to produce the input illuminant
having gidealh impulse characteristic. Our method is experimentally efficient
since only two images need to be measured. Besides it can measure accurately
since the data can be approximated by the conventional MTF model. Next,
we predict the reflectance distribution of halftone print using the measured
MTF in microscopy in order to analyze the dot gain effect since it can
clearly be observed in halftone micro-structure. Finally, a simulation
is carried out to remove the light scattering effect from the predicted
image. Since the simulated image is not affected by the optical dot gain,
it can be applied to analyze the
real dot coverage.
[PDF] (To appeare)