ABSTRACTS
Psychophysical Experiments on the Legibility of Letters
Masami FUNAKAWA
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The visual information available to us decreases selectively
in high-temporal and high-spatial frequency domains as
viewing conditions change for the worse. Visual displays
must therefore be legible in low-visual-acuity conditions
and under conditions of short exposure. We ran three psychophysical
experiments to evaluate legibility under these conditions,
and have come up with several guidelines for display legibility.
We measured the minimum visual acuity needed to discriminate
letters with the low-pass-filtering method and the multi-frame
detection task. The first experiment showed the crucial
effect of letter size on legibility. The results of the
second experiment suggested that the optimal line width
may be determined by a critical band of spatial frequency
describing the letter shape and the power of a low-spatial
frequency. The third experiment showed that background
luminance had a significant effect on the discrimination
of low-contrast letters. In other words, letter contrast
must be about 0.9 in order to avoid the effect of background
luminance.
KEYWORDS: legibility, visibility, visual acuity, contrast
sensitivity, lowpass filtering, letter
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Psychophysical Studies on Legibility and
the Crowding Effect
Masami FUNAKAWA
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Recognizing letters embedded in other letters is difficult.
Framing (boxing) a symbol is thought to make it more conspicuous
or easier to distinguish from the background. However,
the frame may actually affect the legibility of the symbol
adversely. This study evaluates the effects of spatial
arrangement and framing on display legibility. One general
characteristic of vision is that surrounding objects affect
the perception of a central object. This is known as the
crowding effect and is a type of spatial-frequency masking
effect.
We measured the minimum visual acuity required to distinguish
crowded symbols by using the low-pass filtering method
and the multi-frame detection task. The results showed
that a framed symbol, is less legible than an isolated
symbol and that the crowding effect is a function of distance
between the symbol and a mask, and of contrast of the
mask. The spatial spread of the effect was evaluated quantitatively.
KEYWORDS: legibility, visibility, visual acuity, lowpass
filtering, letter |
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Psychophysical Studies on Legibility and
Chromatic Contrast
Masami FUNAKAWA
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Color differences in the CIE 1976 L*a*b* color space
were scaled by measuring the critical area of detection
with a colored patch on a white background. Several colors
were selected to all have the same chromatic contrast
with the white background but differ from one another
in hue. The legibility of numerals painted with the selected
colors were evaluated under Gaussian luminance noises.
We found that red and green numerals were more legible
than yellow and blue ones, despite the equalized chromatic
contrast. The results are explained by differences in
spatio-temporal resolution limits, which were estimated
from the cut-off frequencies of chromatic-contrast sensitivity
functions measured for different hues.
The following properties of color vision must be kept
in mind for coloring a legible display; (1)the low spatio-temporal
resolution of chromatic systems compared with that of
a luminance system; (2)the decolorization in the peripheral
visual field; (3)the deterioration of color discrimination,
caused by aging or several types of color deficiencies;
(4)the wavelength-dependent loss of luminance caused by
aging or several types of color deficiencies; (5)the lower
spatio-temporal resolution for yellow and blue relative
to red and green.
KEYWORDS: color, chromatic contrast, legibility, visibility
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Study on Establishing an Evaluation Method
for the Visibility of the Human Face --Visual Factors Used in
the Evaluation Method and the Composition of Verbal Expressions
Used to Evaluate Visibility--
Shino OKUDA and Ryuji SATOH
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Our study sought to establish a universal and comprehensive
method for evaluating the visibility of the human face.
This paper examines the peculiarity of the human face
as a visual object and the prerequisites required for
an evaluation method. Two experiments were carried out
under various lighting conditions to subjectively evaluate
the visibility of a human face seen through a lace curtain.
These experiments showed that verbal expressions used
to evaluate the whole human face were related to those
used to evaluate each part of the face, and that the luminance
contrast between the cheek and the eye was a visual factor
corresponding to the visibility of the human face.
KEYWORDS: evaluation method, human face, visibility, visual
factor, verbal expression, lace curtain |
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Evaluation of Lighting Environment Using
on Conjoint Analysisi (Part 1)--for the Case of Offices--
Rikuo MURAMATSU and Yoshiki NAKAMURA
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Our study evaluated the lighting environments in offices,
including the trade-offs between various attributes. Conjoint
analysis, common in the field of market research, was
used to evaluate these trade-offs. The attributes were
illuminance, light distribution, glare, design, cost,
usage of natural lighting, and recycling (229 subjects
participated). Consequently, the concept of office-lighting
preferences can be understood quantitatively. That is,
part-worth utilities and attribute importance for all
subjects showed the general characteristics of office-lighting
preferences. Moreover, comparing groups of subjects according
to attribute importance or the subjects' characteristics
suggested valuable methods for understanding office-lighting
preferences in depth.
KEYWORDS: conjoint analysis, evaluation of lighting environment,
quality of lighting environment |
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Analysis of Class-D Electronic Ballast for
Electrodeless Lamps
Futoshi OKAMOTO, Kenshi SUZUKI, Hiroshi KIDO and Toshirou ABE
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We investigated ballast for electrodeless lamps operating
at 13.56 MHz. Higher-efficiency ballast circuits are required
because of problems at high frequency. Our investigation
focused on class-D circuits. We applied numerical model
analysis and conducted experiments to determine the conditions
that maximize efficiency. These conditions occur when
the output current is simultaneous zero and the voltage
across the switching device is virtual zero. We found
that the virtual zero of the voltage is the crossing point
between the zero line and the extrapolation line of the
voltage slope.
KEYWORDS: electrodeless lamps, electronic ballast, class-D
circuit |
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Luminous Intensity Characteristics and Sun-Phantom
Ratio in a Pedestrian Signal Head with a Film Type Lens-Unit
Makoto MIYAUCHI, Teruo SHINOMURA, Masahiro KOUROGI, Shinji HARA
and Takeshi ENDO
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The National Police Agency has yet to propose detailed
specifications for preventing signal head phantoms; they
are currently being examined by the agency. The pedestrian
signal head developed by our project satisfies the standard
for the luminous intensity distribution specified by the
agency. With this film type of pedestrian signal head,
the ratio of signal light to sun phantom was found to
be three times as that of much as current pedestrian signal
heads.
KEYWORDS: film type, pedestrian signal head, luminous
intensity distribution, sun phantom prevention, sun phantom
ratio |
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Effect of Wearing Filter Spectacles to Simulate
the Aging of the Human Lens in the Color Naming of Munsell Color
Chips
Katsunori OKAJIMA and Masanori TAKASE
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Under fluorescent lamp illumination of 500 lx, 429 Munsell
color chips were used in a categorical color naming using
11basic color terms to test how colors appeared to change
when young subjects wore filters that allowed 20-year-olds
to see the outside world as 80-year-olds do. The results
revealed no significant difference in categorical color
naming in terms of apparent-color or surface-color perception.
This suggests that old people can recognize blue colors
for example despite the ocular-spectral-transmittance
change of their aging lenses, and that the color constancy
mechanism plays a critical role in color appearance compensation
for older people.
KEYWORDS: aging color vision, color appearance, color
constancy, basic color terms, categorical color naming |
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Proposal of Practical Method for Calculating
and Indexing Feeling of Contrast for Light Source
Kenjiro HASHIMOTO, Tadashi YANO and Yoshinobu NAYATANI
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"Visual clarity" is considered one of the most important
characteistics of the color rendering properties of light
sources, however, it cannot be adequately estimated by
using the present CIE or JIS Ra method. For this reason,
we previously studied the cause of visual clarity and
found that visual clarity was caused by the feeling of
contrast between colored objects under illumination, and
proposed a new index of the feeling of contrast for a
light source that uses the non-linear color appearance
model by Nayatani et al.
The purpose of the present study is to propose practical
method for calculating and indexing the feeling of contrast
for a light source that uses the CIELAB color space and
CIE chromatic adaptation equation instead of the non-linear
color appearance model by Nayatani et al. A new practical
index of the feeling of contrast for a light source correlated
well with one obtained using the non-linear color appearance
model. Use of this proposed method with the CIE/JIS Ra
method will make it possible to estimate the color rendering
properties of light sources more accurately.
KEYWORDS: color rendering index, light source, feeling
of contrast, visual clarity, brightness sensation |
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