This study investigates perceived neutrality in white light across a range of correlated color temperature (CCT) and Duv values. Two psychophysical experiments were conducted in a dark room using an LCD screen that displayed "white" patches of equal luminance (70 cd/m2) against a black background. In both experiments, 30 observers with normal color vision performed paired comparisons to select the patch that appeared "less tinted" Experiment 1 examined how Duv affected perceived neutrality using 25 white stimuli varying in CCT (3000K, 4000K, 5000K, 6500K, and 9500K) and Duv (0.010, 0.005, 0, -0.005 and -0.010). The results show that the Duv value for the neutral white shifts with CCT: negative below 4000K and increasingly positive above, reaching 0.003 at CCTs higher than 6500K. Experiment 2 assessed the effect of CCT on perceived neutrality across a different CCT range (5000K, 5700K, 6500K, 7700K and 9500K) while maintaining the same set of 5 Duv levels used in Experiment 1. Results indicate the chromaticity associated with the maximum neutrality lies between 7000K and 8000K. The findings of both experiments suggest that the most neutral white corresponds to CIE Illuminant D75, which is specified at 7504K with a Duv of 0.0031. Based on these results, a predictive model of perceived neutrality was developed, defined as a neutral white locus extending from 3000K to 10 000K.

With the increasing prevalence of stereoscopic virtual reality (VR) displays, image sharpness has emerged as a critical factor that influences user experience and visual comfort. Although unsharp masking (USM) is widely used for 2D image enhancement, its perceptual effects in stereoscopic VR environments remain underexplored. We present a psychophysical investigation, using both objective sharpness metrics and subjective user evaluations, of how different USM parameter settings affect visual perception in VR. A series of side-by-side stereoscopic images were processed using various USM parameters and presented on a VR head-mounted display. A total of 33 participants rated each image using five perceptual attributes: perceived sharpness, clarity, naturalness, preference, and depth perception. Modulation transfer function at 50% (MTF50) measurements were used to quantify image sharpness. The results show that MTF50 is highly correlated with perceived sharpness but negatively correlated with naturalness and preference, suggesting that over-sharpening may degrade image realism. Depth perception was most enhanced in low-frequency scenes, whereas clarity scores exhibited weak or no correlation with MTF50. These findings provide insights into the trade-offs of sharpness tuning in stereoscopic VR imaging and offer guidance for optimizing image-processing pipelines to balance perceived quality and viewer comfort in immersive applications.

As display technology advances in color gamut, the potential of experiencing higher degree of observer metamerism is more likely with narrow bandwidth stimuli display devices. In previous studies, it is confirmed that observer metamerism was introduced in soft proofing with monitor and color grading with projector scenarios, and also led to serious implications. Hence, it is desired to investigate whether laser-based projection system would introduce observer metamerism compared to halogen-based projection system. In this study, a two-part experiment was designed and conducted. Experiment 1 was based on color patches and experiment 2 was based on test images. Intra-observer and inter-observer variability were calculated and analyzed. Both experiments had illustrated observer metamerism was introduced in laser-based projection system. Comparison to CIE Standard Observers was also conducted for each experiment, and the results had suggested that the CIE Standard Observers were not suitable for laser-based projection system. A new observer category was required at least for the group of observers participating the experiments. A quick method to transform the content from the CIE 1964 Standard Observer for color patches or the CIE 1931 Standard Observer for images has been established in experiment 1, and this quick method could help to facilitate the growth of personalized color management system.

E-reading devices are becoming more and more common in our daily life, and they are used under a wide range of ambient light levels, from completely dark to extremely bright conditions. In this study, a psychophysical experiment is carried out to investigate how ambient light level affects the visual comfort of an e-reading device. Human observers compare the visual comfort of pairs of different text-background lightness combinations on a tablet device under three ambient light levels (i.e., 150, 1500, and 15,000 lx). With our previous work, the experimental results show that the trend of visual comfort interval scales below 1500 lx (i.e., Dark, 150, 300, and 1500 lx) are similar to each other but not for those under illuminance above the 1500 lx (i.e., 3000 and 15,000 lx). For the same lightness difference between text and background, the observers tend to read the text with a white background compared to a black background, especially for 3000 and 15,000 lx. Moreover, a black text on a light-gray background is the most comfortable combination under these two illuminance levels. An evaluation model is proposed based on ambient illuminance, screen parameters, and visual estimation to design an optimal viewing condition when reading on the tablet display.

The present study took a meeting room as an example to investigate how direct lighting and indirect lighting can affect visual impressions of a VR space.This study adopted 10 lighting designs for the room, and each design was assessed via 7 semantic scales.Experimental data show good repeatability for all but the relaxing/nervous scale, with correlation coefficients for each scale between visual responses given for the first time and those for the second time.The results indicate that direct lighting has a greater impact than indirect lighting on some visual impressions of the room.

Psychophysical experiments of colour appearance, in terms of lightness, colourfulness, and hue, were conducted outdoors and indoors to investigate whether there was any difference in colour appearance between outdoor and indoor environments. A panel of 10 observers participated in the outdoor experiment, while 13 observers took part in the indoor experiment. The reference white had an average luminance of 12784 cd/m(2) in the outdoor experiment and 129 cd/m(2) in the indoor experiment. Test colours included 42 colour patches selected from the Practical Coordinate Color System to achieve a reasonable uniform distribution of samples in CIECAM02. Experimental results show that for both outdoor and indoor environments, there was good agreement between visual data and predicted values by CIECAM02 for the three colour appearance scales, with the coefficient of variation values all lower than 25 and the R-2 values all higher than 0.73, indicating little difference in the three dimensions of colour appearance between indoor and outdoor viewing conditions. Experimental data also suggest that the observers were more sensitive to variation in lightness for grayish colours than for highly saturated colours, a phenomenon that seems to relate with the Helmholtz-Kohlrausch effect. This phenomenon was modeled for predicting perceived lightness (J ') using the present experimental data. The new J ' model was tested using three extra sets of visual data obtained both outdoors and indoors, showing good predictive performance of the new model, with an average coefficient of variation of 14, an average R-2 of 0.88, and an average STRESS index of 14.18.

Two psychophysical experiments were carried out to investigate the relationship between wallpaper patterns and visual impressions.Experiment 1 used single wallpaper patterns as the stimuli, whereas Experiment 2 used wallpaper pattern pairs as the stimuli for the visual assessment.A total of 11 wallpaper patterns were used in this study.Ten 6-point forced choice scales were used in both experiments: simple/complex, warm/cool, relaxing/heavy, comfortable/uncomfortable, lively/dull, unique/common, fashionable/unfashionable, splendid/ plain, beautiful/ugly and like/dislike.As a result, principal component analysis identifies two underlying factors of the visual responses for Experiment 1, "liveliness" and "simplicity".The observers tended to prefer wallpaper patterns that appeared beautiful, comfortable, relaxing or lively.They also tended to prefer light patterns to dark patterns.Experiment 2 reveals that the "mean value" method can apply to non-aesthetics-related scales, such as simple/complex, warm/cool, relaxing/heavy, comfortable/uncomfortable, lively/dull, fashionable/unfashionable and splendid/plain.

A psychophysical experiment was carried out to investigate how light source chromaticities affected unique hue judgements using Munsell samples at two chroma levels.Ten observers between 20 and 23 years of age (mean = 21, std.dev.=1) participated in the experiment.Each observer was asked to select the unique hues from the 40 V6C8 (Value 6 Chroma 8) Munsell samples and 40 V8C4 (Value 8 Chroma 4) Munsell samples under six light sources.The experiment results showed that the hue angles defined in CIECAM02 were similar to the unique red and green judgments made by the observers, but not to the unique blue and yellow judgements.For unique blue, the observers' judgements generally shifted toward green.The observers' judgements on unique yellow varied with the chroma levels of the samples and Duv levels of the light sources.

This study aimed to investigate colour appearance in virtual reality (VR).A total of 35 test colours were visually assessed in a VR space by 16 observers in terms of lightness, colourfulness and hue quadrature.The experimental results show high correlation between perceived colour appearance and predicted values by CIECAM02, with a correlation coefficient of 0.96 between perceived lightness and CIECAM02 J, 0.99 between perceived hue quadrature and CIECAM02 H, and 0.88 between perceived colourfulness and CIECAM02 M.

A psychophysical experiment was carried out to investigate visual response in a lit environment.During the experiment, the illuminance level will vary at different times of a day.Five colournormal observers (2 males and 3 females), between 22 and 29 years of age, participated in the study.They were asked to assess the room in terms of 5 scales, liking, comfort, excitation, safety, and brightness, using a 6-point forced-choice categorical judgement scaling method.The experimental results show that the scale value tends to decrease in the morning until midday and tends to increase in the afternoon.Based on evaluation results obtained at each timeslot, high correlation was found between brightness and safety at the start of timeslot.For the end of timeslot, the perceived brightness is highly correlated with liking rather than safety.

Many tablets are designed to change display brightness or color with surround for enhancing visual comfort. Although both color and brightness of a surround may vary a lot, few studies investigated how text-background lightness combination of a tablet display and surround jointly affect visual comfort, and how display white point affects visual comfort. In this study, 20 observers evaluated visual comfort of 20 text-background lightness combinations of a 9.7-inch tablet display through paired comparisons under five surrounds-a dark surround and four ambient lighting conditions comprising two levels of correlated color temperature (CCT)-3500 and 6500 K-and illuminance-300 and 3000 lx. The combination of a black text and a light-gray background (i.e., L-background(*) = 75.33; L-text(*) = 1.6) was evaluated the most comfortable when there was ambient light regardless of CCT and illuminance. It was also evaluated the third most comfortable under the dark surround. The observers also evaluated the visual comfort of a dark text on five different white backgrounds under 3500 and 6500 K at 1000 lx. The color of the background that was judged as the most comfortable neither had the whitest appearance nor matched the color of the ambient light. The simultaneous adjustment of the display white point and the text-background lightness combination merits further investigations.

The preference and visual impression of human faces were investigated using various lighting settings including luminance and direction of lighting.Thirty observers assessed preference and visual impressions of 48 sculpture images shown on an LCD display.The results show strong connections between light directions and visual impressions, and between luminance contrast in the sculpture image and the visual impressions.The results indicate that the observers tended to have positive impressions for sculpture images with the light coming from the top rather than from the bottom.In addition, the observers tended to have positive impressions for sculpture images with a small luminance contrast rather than a large contrast.This implies that we can use various lighting conditions to evoke various moods from the observers.

To investigate the influence of colour on visual conspicuity on subway route maps, two experiments were conducted in this study.Experiment 1 was the main experiment, aiming to develop a visual conspicuity model based on the experimental results.The experiment used coloured subway route maps as the stimuli, generated from a 15-route map designed by the research team, with the route colours varied for each test.During the experiment, each observer was asked to identify as fast as possible whether a target coloured route was present on that map, and the observer's reaction time was recorded for each test.The experimental results show that the larger colour difference between the target route and the other routes, the better visual conspicuity for the target.Experiment 2 was a verification test of this finding, showing a good predictive performance of the developed model in this study.

With the development of tablet display technology, using tablet has become more and more popular for people to read news and messages. For enhancing visual comfort, many tablets are designed to change display brightness or color with surrounding conditions. Few studies, however, investigated how text-background lightness combination of a tablet should change when the color and light level of a surround change simultaneously, especially under very high light level (e.g., under daylight). In this study, twenty observers evaluated visual comfort of 20 text-background lightness combinations on an iPad Air 2 through paired comparisons under five surrounds—a dark surround and four ambient lighting conditions, comprising two levels of CCT (i.e., 3500 and 6500 K) and illuminance (i.e., 300 and 3000 lx). The observers judged the combination of black text with a light grey background (i.e., L*background = 75.33 and L*text = 1.6) the most comfortable when there was ambient light regardless of CCT and illuminance. This combination was also evaluated as the third most comfortable under the dark surround.

This article describes the development of new models for predicting four colour appearance attributes: saturation, vividness, blackness, and whiteness. The new models were developed on the basis of experimental data accumulated in the authors' previous study, in which the four colour appearance attributes were scaled by 64 Korean and 68 British observers using the categorical judgment method. Two types of models were developed: the ellipsoid-based and the hue-based. For the former, the perceived saturation, vividness, blackness, and whiteness were modeled in the form of colour-difference formulae between the test colour and a reference colour. For the latter, blackness, whiteness, and chromaticness scales were modeled by estimating hue-dependent lightness and chroma values for the full colour in the framework of Adams' equation. The new models were tested using NCS data and were found to outperform some of the existing colour appearance models.

Past studies investigating the unique hues only used samples with a relatively high saturation levels under standard illuminants. In this study, 10 observers selected the four samples with unique hues from 40 V6C8 (Value 6 Chroma 8) and 40 V8C4 (Value 8 Chroma 4) Munsell samples under six light sources, comprising three levels of D-uv (i.e., 0, -0.02, and -0.04) and two levels of correlated color temperature (i.e., 2700 and 3500K). Significant differences were found between the two chroma levels for unique blue and yellow, with the hue angles of unique yellow and blue judged using the desaturated samples being significantly different from those defined in CIECAM02. The iso-lines of unique yellow, blue, and green did not always go through the origin of the a*-b* or a-b planes in CIELAB and CAM02-UCS. Thus, the problems of CIECAM02, CIELAB, and CAM02-UCS identified in this study need further investigations.

In comparison to the great efforts made on the enhancement of image quality for tablet displays, little attention has been paid on the concept of white point. Given the increasing popularity of the light sources with chromaticities off the Planckian locus and color-tunable LED lighting, it is important to investigate human's white perception of tablet display under different ambient lighting conditions. This study investigated the white appearance of a tablet display under 17 ambient lighting conditions, including a dark condition, seven conditions with chromaticities on the Planckian locus, and nine conditions with chromaticities off the Planckian locus, (i.e., Duv = + 0.02, -0.02, and -0.04). It was found that both the white appearance boundary defined by the fitted one-standard-deviation error ellipse and the whitest stimulus rated by the observers or identified by the bivariate Gaussian distribution were different under the various ambient lighting conditions. The optimization based on the whitest stimulus under each ambient lighting condition suggested a lower degree of chromatic adaptation under the conditions with a lower Correlated Color Temperature (CCT). For the conditions with a same CCT, a Duv of -0.02 was found to provide a higher degree of chromatic adaptation than Duv values of + 0.02 and -0.04.