Journal of Light
&
Visual Environment

Volume 28 Number 1, April 2004

CONTENTS

Papers

Research Note

English Abstracts

 A method is described for estimating three-dimensional(3D) shapes from two-dimensional(2-D) shading information in gray-level images that uses the diffuse reflection components in a luminance distribution with diffuse and specular reflection components. It overcomes the problem of highlights caused by the specular reflection components that occurs when multiple fixed light sources are used, which is a drawback to the "photometric stereo" method proposed by Woodham. First, the bi-directional reflectance distribution function is estimated for the detected area of a gray-level image with highlights. Then, the luminance distribution caused by the diffuse reflection components in the detected area is estimated based on the luminance distribution in a gray-level image without highlights. Numerical shape-measurement experiments using mixed diffuse-specular objects with different characteristic reflectances and shapes showed that the proposed method can accurately measure the 3-D shape of mixed diffuse-specular objects.

KEYWORDS:bidirectional reflectance distribution function, reflection characteristic, photometric streo, highlights, shape measurement, mixed diffuse-speculer objects

 Two methods are used for color matching : visual color matching and CCM(computerized color matching) which is now used quite frequently. Although CCM decrease the color difference more easily, color correction must be repeated in the case of unstable color development due to the limited coloring reproducibility. There is no CCM system to display coloring reproducibility. A previous report described how coloring reproducibility can be displayed by using the spectral differences between the measured and CCM simulated spectral reflectance of color matching samples. The main point of the study reported here is identification of the coloring agents causing poor coloring reproducibility. It is especially important to identify the achromatic coloring agent. It become possible by the following methods. The spectral defference between the measured and simulated spectral reflectance of the abnormal color matching sample includes the abnormal component and the original simulation error. The quantity of the colorants of the abnormal sample is calculated by means of offsetting the original simulation error. The colorants causing abnormalities can be identified based upon the changing ratio of each colorant versus the recipes of the colorants originally planned to manufacture.

KEYWORDS:CCM, computer, color, matching, coloring, reproducibility

 We use the maximum level of individual visual acuity (MVA) as an index for the individual visual ability. Also, we define the concept of the ratio of visual acuity under various environmental conditions for the MVA as Visual Acuity Ratio (VAR), in order to describe differences between individual visibilities.

 An experiment was carried out using various levels of background luminance and visual distance. The visual acuity of subjects in two age groups (Young and Aged) was measured by using Landolt’s eye chart (luminance contrast: 0.93). The Aged subjects’ vision was corrected by two kinds of spectacles: ones for myopia / presbyopia.

 Under conditions providing sufficient visual acuity, the subjects’ order of individual visual acuity was unchanged. Therefore, MVA can be used as an index for the visual ability of the individual. Regardless of corrected conditions, the individual visual acuity reaches the maximum level under 800cd/m² and the corrected position. The results of the eyesight test can be used as a substitution for MVA.

 Visual acuity is changing under environmental conditions, and a degree of the changes varies with age, corrected conditions, and differences in visual acuity. Under the corrected position, the relationship between background luminance and VAR is constant regardless of age group, corrected conditions and differences of visual acuity. The relationship between visual distance and VAR differs by age and corrected conditions. However, in the neighborhood of the corrected position, the relationship between visual distance and VAR is constant regardless of differences between individual visibilities. The concept of VAR is applicable to past studies.

KEYWORDS:visual acuity, luminance, visual distance, visual acuity ratio, age, individual differences

 Understanding illumination is necessary for the perception of color and brightness in an object’s surface. We call such understanding the recognized visual space of illumination, or RVSI. In particular, we use the term ‘brightness size’ of RVSI to describe an observer’s perception about the intensity of illumination. The brightness size of RVSI is evaluated using the border luminance between surface color and unnatural surface color modes. We established a new estimation method of space brightness in natural environments and investigated what determines the brightness size of RVSI. We measured the border luminance of the test patch (N5 gray, mat) to test three candidates for determining the size: illuminance (1), spatially averaged luminance across a visual field (2), and highest luminance (3). The border luminance was proportional to the illuminance and was almost equal to the luminance of the object with the highest lightness. However, there was no effect from the luminance of the object with the light-source color mode, regardless of its luminance. The effect from the averaged luminance was not significant. We concluded the illuminance to be a major determinant of the brightness size of RVSI.

KEYWORDS: space brightness, recognized visual space of illumination (RVSI), brightness size of RVSI, color appearance mode, natural environment

 This study aims enable light pollution to be compared with other major environmental issues by estimating the economic values of light pollution based on the Contingent Valuation Method (CVM). Furthermore, through reviewing the relationship between the economic values estimated by CVM, and the level of the subject’s environmental consciousness and environmental friendly behaviors, this study attempts to precisely understand people’s consciousness of light pollution.

KEYWORDS: contingent valuation method, light pollution, environmental assessment

 The choice of new signaling and safety equipment for track circuits is dependent on individual railway management organizations. For that reason, before making any decisions, railway management has to be very well informed about all parameters relevant to the electro-magnetic compatibility with return traction current during stationary regimes of operation. An examination is neccesary of external electro-magnetic interference to return traction current on track circuit operations must identify suitable protection measures to ensure secure and reliable track circuit operations. Building on that requirement, this work describes results of mathematical modelling which examined the impact of return traction current through railway tracks on the proper functioning of signaling and safety systems in the track system. This mathematical model has been tested through experimentiion on electrified tracks belonging to the Yugoslav Railways.

KEYWORDS:electric locomotive, return traction current, signaling equipment

 In order to facilitate use of daylighting in architectural design, we tried to measure the suitability of luminous environment for various behavior, including not only visual work but also refreshing and rest. An experiment was conducted with 7 luminous conditions including daylighting. The suitability of a luminous environment was measured by asking the subjects to select suitable activities and unsuitable behaviors from a given list of possible activities. The result showed the selection of unsuitable behaviors was more useful than the selection of suitable behaviors. Furthermore, lighting installations offering a steady luminous environments, were not suitable for many behaviors including refreshing and rest. The luminous environments which were bright but had some fluctuation and some non-uniformity of brightness, obtained by use of direct sunlight, were judged to be suitable for negotiating,refreshing, and meeting.

KEYWORDS:luminous environment, suitability, behavior, subjective experiment