Hong-Suk Kim

Spatial Luminance Contrast Sensitivity: Effects of Surround

This study examined the effects of surround luminance on the shape of the spatial luminance contrast sensitivity function (CSF). The reduction in brightness of uniform neutral patches shown on a computer controlled display screen is also assessed to explain the change of CSF shape. Consequently, a large amount of reduction in contrast sensitivity at middle spatial frequencies can be observed; however, the reduction is relatively small for low spatial frequencies. In general, the effect of surround luminance on the CSF appears similar to that of mean luminance. Reduced CSF responses result in less power of the filtered image; therefore, the stimulus should appear dimmer with a higher surround luminance.

Measuring of the Perceptibility and Acceptability in Various Color Quality Measures

Perceptibility and acceptability are the most often used threshold units in the field of color science. The former refers to a just perceptible difference and the latter evokes a tolerable color difference. Such thresholds can be very significant to color quality control processes in the printing industry and should be defined in quality measure units. Optical density (OD) and color difference models are usually utilized as color quality measures and have been provided in a considerable number of commercial measuring devices such as spectrophotometers. However, their merits and traits are far less understood in the literature. The present study intends to evaluate performance of those color quality measures including the OD and widely known color difference models, e.g. ΔE*ab ΔECMC(l:c) and ΔE*00. A set of psychophysical assessments were carried out in order to accumulate the perceptibility and acceptability thresholds data, and their central trend was compared with the color quality measure estimates.

Determination of the Perceived Contrast Compensation Ratio for a Wide Range of Surround Luminance

It is established that the perceived image contrast is affected by surround luminance. In order to get the same perceived image contrast, the optimum surround compensation ratios for those surround conditions is needed. Much research has been performed for dark, dim, and average surrounds. In this study, a wide range of surround luminance from dark up to

Recovering the Colors of Objects from Multiple Near-IR Images

2087cd/m^2

The Analysis of Emotion Adjective for LED Light Colors by using Kobayashi scale and I.R.I scale

was considered. Using magnitude estimation method, the change in perceived brightness of six test stimuli was measured under seven surround conditions; dark, dim, 2 levels of average, bright, and 2 levels of over-bright surrounds. To drive the perceived image contrast from the perceived brightness, two different definitions of contrast were tested. Their calculated results were compared with the visual data of our previous work. And to conclude, the perceived contrast compensation ratios were 1:1.11:1.2 for average, dim and dark surrounds. These were close to CIECAM02 model (1:1.17:1.31). Besides, for average, bright, over-bright1 and over-bright2 surrounds the ratios 1:1.17:1.42:1.69 were determined. For intermediate or more extreme surround conditions, the compensation ratio was obtained from the linear interpolation or extrapolation.

Measurement of the optimum surround ratio inducing the highest perceived image contrast

This paper proposes an algorithm for recovering the colors of objects from multiple near-infrared (near-IR) images. The International Commission on Illumination (CIE) color coordinates of objects are recovered from a series of gray images captured under multiple spectral near-IR illuminations using polynomial regression. The feasibility of the proposed algorithm is tested experimentally by using 24 color patches of the Color Rendition Chart. The experimental apparatus is composed of a monochrome digital camera without an IR cut-off filter and a custom-designed LED illuminator emitting multiple spectral near-IR illuminations, with peak wavelengths near the red edge of the visible band, namely at 700, 740, 780, and 860 nm. The average color difference between the original and the recovered colors for all 24 patches was found to be 11.1. However, if some particular patches with high value are disregarded, the average color difference is reduced to 4.2, and this value is within the acceptability tolerance for complex image on the display.

A Study on the Operational Characteristic with the Scale Effect of the Cross-Flow Fan

The aim of this study is to analyze the emotion adjectives for light emitting diode(LED) light colors using a twofold adjective image scales from Kobayashi and I.R.I. A set of psychophysical experiments using category judgment was conducted in an LED light color simulation system, in order to evaluate each emotion scale coordinate for those test light colors in both adjective image scales. In total, 49 test light colors from a combination of 6 color series were assessed by 15 human observers. As a result, Kobayashi adjective image scale clearly expressed to emotion adjectives of `Dynamic`, `Casual`, `Chic`, `Cool-casual`, `Modern`, and `Natural` for different hues. In contrast, I.R.I adjective image scale expressed only 2 adjectives of `dynamic` and `luxurious` for the all hues.

Human vision based color edge detection

Much research has shown that perceived image contrast increases as the surround luminance increases, but a number of recent studies reported opposite trends under higher surround luminance levels. We measured the change in perceived image contrast under a wide range of surround luminance levels covering from dark up to 2087 cd/m2. A large-area illuminator was used to illuminate the surround. It consists of 23 dimmable fluorescent lamps and a diffuser. Its maximum luminance is 2087 cd/m2 and could be adjusted to six lower levels. A set of paired comparison experiments was conducted to compare the perception of image contrast under seven different surround luminance levels. The results showed that the perceived image contrast varies with surround luminance and the maximum perceived image contrast is found near a surround ratio (SR) of 1. As SR increases from 0 to 1, the z score is increased, which can be fully expected by the Bartleson and Breneman effect. However, it is drastically decreased in the region of SR > 1; thus, the perceived image contrast is eventually decreased.

The Analysis of Fatigueness and Preference for Three Appearance Attributes of LED Light Color

One of noticeable features in the cross flow fan is that a working fluid passes through impeller blade twice without distinction between the inlet and exit angles. Also, it does produce higher circumferential velocity than other types of blade at the same flow rate in accordance with the application of the forward curved shape. However, a design theory for the cross-flow fall has not yet been formed owing to an eccentric vortex, which is the remarkable characteristics, occurred in a cross-flow fan. Furthermore, the eccentric vortex, which is difficult to control the size and position, is the important cause of performance decrease. In this study, experiments we carried out to estimate the similarity of the cross-flow fan with various scales and rotational velocity changes. Pressure coefficients to flow coefficients with various scales of the cross-flow fan are plotted to the application of the general similarity law of the turbomachinery in the cross-flow fan with Archimedes spiral, which is the important factor having an effect on it.

Brightness contrast under high surround luminance levels: psychophysical data vs CIECAM02

Edge detection can be of great importance to image processing in various digital imaging applications such as digital television and camera. Therefore, extracting more accurate edge properties are significantly demanded for achieving a better image understanding. In vector gradient edge detection, absolute difference of RGB values between a center pixel value, and its neighborhood values are usually used, although such a device-dependent color space does not account for human visual characteristics well. The goal of this study is to test a variety of color difference equations and propose the most effective model that can be used for the purpose of color edge detection. Three of synthetic images generated using perceptibility threshold of the human visual system were used for objectively evaluate to 5 color difference equations studied in this paper. A set of 6 complex color images was also used to testing the 5 color difference equations psychophysically. The equations include ΔRGB, ΔE* ab, ΔECMC, CIEDE2000 (ΔE00) and CIECAM02-UCS delta E (ΔECAM-UCS). Consequently, there were not significant performance variations observed between those 5 color difference equations for the purpose of edge detection. However, ΔE00 and ΔECAM-UCS showed slightly higher mean opinion score (MOS) in detected edge information.