Robust pixel-wise illuminant estimation algorithm for images with a low bit-depth.

Conventional illuminant estimation methods were developed for scenes with a uniform illumination, while recently developed methods, such as pixel-wise methods, estimate the illuminants at the pixel level, making them applicable to a wider range of scenes. It was found that the same pixel-wise algorithm had very different performance when applied to images with different bit-depths, with up to a 30% decrease in accuracy for images having a lower bit-depth. Image signal processing (ISP) pipelines, however, prefer to deal with images with a lower bit-depth.

Effective cross-sensor color constancy using a dual-mapping strategy.

Deep neural networks (DNNs) have been widely used for illuminant estimation, which commonly requires great efforts to collect sensor-specific data. In this paper, we propose a dual-mapping strategy-the DMCC method. It only requires the white points captured by the training and testing sensors under a D65 condition to reconstruct the image and illuminant data, and then maps the reconstructed image into sparse features.

Color difference evaluations on metameric color stimuli by observers of three age groups.

Color matching functions (CMFs), which are used to derive tristimulus values and chromaticities, play a very important role in color characterization, calibration, and specifications. Great efforts have been made to investigate how CMFs can characterize the color matches and mismatches between stimuli with different spectral compositions under different sizes of field of view (FOV). Few study specifically investigated how to better characterize the CMFs for different observer ages.

Color constancy from a pure color view.

Great efforts have been made on illuminant estimation in both academia and industry, leading to the development of various statistical- and learning-based methods. Little attention, however, has been given to images that are dominated by a single color (i.e.

The Effects of Light Therapy on Sleep, Agitation and Depression in People With Dementia: A Systematic Review and Meta-analysis of Randomized Controlled Trials.

Objective: To evaluate the effects of light therapy on the alleviation of sleep disturbances, agitation and depression in people with dementia.

Methods: A search was performed in PubMed, Medline, SCOPUS, Web of Science, EMBASE, CINAHL, Cochrane Library, for studies published between 2000 and 2021.

Results: A total of 4315 articles were screened.

Constant hue loci in different color spaces for stimuli in Rec. 2020 color gamut and HDR conditions.

Hue is an important attribute for characterizing a color stimulus, which is also an output in various color spaces. The investigations on the hue linearity and constant hue loci for different color spaces were generally conducted using conventional CRT displays or surface color samples, in which the color stimuli were within small color gamuts and viewed under standard dynamic range conditions. With the development of imaging technologies, the hue linearity and constant hue loci need to be investigated for wide color gamuts and high dynamic range conditions, which is critically important for image processing (e.

Effect of observer age and stimulus size on the performance of CIE color matching functions.

Both observer age and size of stimulus as characterized using the field of view (FOV) are two important parameters to affect the color matching functions (CMFs) of human observers. They are also included in the cone fundamental and CMFs models that were recently proposed by the International Commission on Illumination (CIE) in 2006. In contrast to the great number of studies investigating the performance of CMFs in characterizing color matches and mismatches using different primary sets, few study investigated the effect of CMFs in characterizing these two factors.

Effect of primary peak wavelength on color matching and color matching function performance.

With the development of wide color gamut displays, several recent studies investigated the performance of the CIE standard color matching functions (CMFs) in characterizing the color matches and observer metamerism between different primary sets. These studies, however, always employed different primaries to produce color stimuli, which failed to isolate the effect of the peak wavelength from that of the spectral shape. In this study, we carefully selected primaries with similar spectral shapes but different peak wavelengths.

Color mismatch and observer metamerism between conventional liquid crystal displays and organic light emitting diode displays.

Organic light emitting diode (OLED) displays use red, green, and blue primaries with a higher saturation level to produce larger color gamuts than conventional liquid crystal displays (LCD). No past study, however, experimentally investigated how such a difference between these two display types causes color mismatch and observer metamerism using the most widely used color matching functions (CMFs)-the CIE 1931 2° CMFs-for color calibration and specification. In this study, 50 human observers performed color matching tasks for six color stimuli with a field-of-view of 4.

Observer metamerism to display white point using different primary sets.

Displays with different primary sets were found to introduce perceived color mismatch between stimuli that are computationally metameric and to affect the variations of the perceived color difference of metameric stimuli among observers (i.e., observer metamerism).

Investigating unique hues at different chroma levels with a smaller hue angle step.

Unique hue plays a critical role in color appearance models and uniform color spaces. Past studies investigating unique hues commonly used 40 Munsell samples with the same chroma and lightness levels to produce color stimuli, with a hue angle step of 9°. These 40 samples were always simultaneously presented to the observers.

Assessing the temporal uniformity of CIELAB hue angle.

In recent work [J. Opt. Soc.

Effects of adapting luminance and CCT on appearance of white and degree of chromatic adaptation.

Past studies reported that the degree of chromatic adaptation was affected by viewing medium and adapting luminance. In this study, human observers adjusted the color appearance of a stimulus produced by a self-luminous display to make it appear as white as possible under different adapting conditions, whose adapting luminance and Correlated Color Temperature (CCT) levels were systematically varied. Though an identical display was used as the viewing medium, the chromaticities adjusted under the high adapting luminance levels were generally around the adapting chromaticities, which was similar to the findings in the past studies using reflective surface color samples as the viewing medium.

Development of a whiteness formula for surface colors under an arbitrary light source.

The whiteness specification is critically important in surface color industry, especially when fluorescent whitening agents (FWAs) are added to objects. The CIE whiteness formula, the most widely used whiteness formula, only characterizes the whiteness under CIE standard D65, which ignores the change of whiteness under different light sources due to the spectral content of the light sources. Though the adoption of a Chromatic Adaptation Transform (CAT02) in the CIE whiteness formula was found effective in recent studies, it failed to allow a comparison across different correlated color temperatures (CCTs).

White appearance of a tablet display under different ambient lighting conditions.

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.

Evaluation of whiteness formulas for FWA and non-FWA whites.

Whiteness is an important colorimetric characteristic for surface colors. Currently, the CIE whiteness formula is widely used to characterize the whiteness of a surface in industry, whose limitations have been well documented. In this study, the whiteness appearance of 55 textile samples [43 non-fluorescent whitening agents (FWAs) and 12 FWA samples] were evaluated under six lighting conditions, comprising three levels of correlated color temperature (CCT) (i.

Development of the IES method for evaluating the color rendition of light sources.

We have developed a two-measure system for evaluating light sources' color rendition that builds upon conceptual progress of numerous researchers over the last two decades. The system quantifies the color fidelity and color gamut (change in object chroma) of a light source in comparison to a reference illuminant. The calculations are based on a newly developed set of reflectance data from real samples uniformly distributed in color space (thereby fairly representing all colors) and in wavelength space (thereby precluding artificial optimization of the color rendition scores by spectral engineering).

Eye movement and pupil size constriction under discomfort glare.

Purpose: Involuntary physiological responses offer an alternative means to psychophysical procedures for objectively evaluating discomfort glare. This study examined eye movement and pupil size responses to glare discomfort using new approaches to analysis: relative pupil size and speed of eye movement.

Methods: Participants evaluated glare discomfort using the standard de Boer rating scale under various conditions manipulated to influence glare discomfort.

Review of measures for light-source color rendition and considerations for a two-measure system for characterizing color rendition.

Twenty-two measures of color rendition have been reviewed and summarized. Each measure was computed for 401 illuminants comprising incandescent, light-emitting diode (LED) -phosphor, LED-mixed, fluorescent, high-intensity discharge (HID), and theoretical illuminants. A multidimensional scaling analysis (Matrix Stress = 0.

Research on a method to measure the optical parameters of a precision approach path indicator.

The precision approach path indicator (PAPI) system is installed alongside a runway or at a heliport to provide accurate visual approach path information to pilots of landing aircraft, either day or night. The indicator sends the information through different color combinations. The international standards have very rigid requirements for the intensity distribution and the transition angle from red light to white light of the indicator.