Kaida Xiao

University of Leeds · Colour Imaging, Graphcs and Appearance Management

The paper describes a comprehensive test to evaluate the performance of current colour‐difference models using available experimental datasets. In total, 28 individual datasets were accumulated to test 17 colour‐difference formulae, 13 of them based on Uniform Colour Spaces (UCSs) in terms of the Standardized Residual Sum of Squares (STRESS) measur...

Previous research has demonstrated the potential to reconstruct human facial skin spectra based on the responses of RGB cameras to achieve high-fidelity color reproduction of human facial skin in various industrial applications. Nonetheless, the level of precision is still expected to improve. Inspired by the asymmetricity of human facial skin colo...

Based on previous visual assessments of 440 color pairs of 3D-printed samples, we tested the performance of eight color-difference formulas (CIELAB, CIEDE2000, CAM02-LCD, CAM02-SCD, CAM02-UCS, CAM16-LCD, CAM16-SCD, and CAM16-UCS) using the standardized residual sum of squares (STRESS) index. For the whole set of 440 color pairs, the introduction of...

A new interim and connection space (ICS) and its reconstruction method are proposed. The proposed ICS, t D 65 A , consists of six colorimetric values or two sets of tristimulus values under CIE illuminant D65 and A respectively. In addition, a new spectral decomposition based on the t D 65 A ICS and the Wiener Estimation matrix M W was introduced f...

The digital archive of cultural heritage provides new opportunities for the protection of the cultural heritage and the development of online museums. One of the essential requirements for the digitization is to achieve accurate color reproduction. Taking the Imperial Chinese robes in the Qing Dynasty as an example, this study aims to develop a dig...

Facial colour characteristics convey vital personal information and influence social interactions and mate choices as contributing factors to perceived beauty, health, and age. How various colour characteristics affect facial preference and whether there are cultural differences are not fully understood. Here, we provide a useful and repeatable met...

The current color-difference formulas were developed based on 2D samples and there is no standard guidance for the color-difference evaluation of 3D objects. The aim of this study was to test and optimize the CIELAB and CIEDE2000 color-difference formulas by using 42 pairs of 3D-printed spherical samples in Experiment I and 40 sample pairs in Exper...

In order to study the influence and mechanisms of color differences using 3D-shaped objects, 440 pairs of 3D samples surrounding five CIE color centers (gray, red, yellow, green, and blue) with the variations of gloss, size, and shape were prepared by a Sailner 3D color printer, and their color differences were assessed by 26x45 observers using the...

We performed spectrophotometric measurements of skin reflectance at four body locations (forehead, cheek, neck, and back of hand), before and after two weeks of sun exposure, for 103 first-year college students. Skin reflectance was measured twice at each body location, before and after two weeks of sun exposure, obtaining an average repeatability...

Facial colour characteristics convey vital personal information and influence social interactions and mate choices as contributing factors to perceived beauty, health, and age. How various colour characteristics would affect facial preference and whether there is a cultural difference are not fully understood. Here, we provide a useful and repeatab...

An improved spectral reflectance estimation method was developed to transform captured RGB images to spectral reflectance. The novelty of our method is an iteratively reweighted regulated model that combines polynomial expansion signals, which was developed for spectral reflectance estimation, and a cross-polarized imaging system, which is used to...

The influence of light sources on digital camera-based spectral estimation is explored. The CIE daylight and non-CIE daylight illuminants with different Correlated Color Temperature (CCT) are first tested comparatively, results indicate that CCT can be used to describe the performance of the CIE daylight illuminants for spectral estimation but not...

As functional 3D printing becomes more popular with industrial manufacturing applications, it is time to start discussing high-fidelity appearance reproduction of 3D objects, particularly in faithful colors. To date, there is only limited research on accurate color reproduction and on universal color reproduction method for different color 3D print...

Facial skin coloration signals information about an individual and plays an important role in social interactions and mate choice, due its putative association with health, attractiveness, and age. Whether skin coloration as an evolutionary significant cue is universal or specific to a particular culture is unclear and current evidence on the unive...

In this study, an image-based measurement system was developed for human facial skin colour, involving the development of a digital imaging system, collection of facial skin colour from 60 human subjects, generation of different colour characterization models, and performance evaluation. The factors that affect facial skin colour characterization,...

We have described a number of transformations by mapping the cone signal vector , formed by , to opponent space , formed by achromatic signal , red-green signal and yellow-blue signal . Two new transformations, and , are proposed, based on the CIE 2006 spectral luminous efficiency function, , and Hurvich's opponent spectral red-green and yellow-blu...

This research is aimed to better understand human perception of skin colour and quantify the overall colour appearance of human faces. In this study, a colour matching experiment was conducted and the overall facial colour appearance of 80 facial images, including 40 Caucasian faces and 40 Chinese faces, were obtained. The main finding of this stud...

This paper presents the results of experiments to evaluate the human perception of the visual-tactile properties: flexible-stiff, smooth-rough and soft-firm of fabrics as seen on a mobile-phone display. The aim of this study was to test whether different colours and different fabrics have significant effects on these properties, and to evaluate the...

For digital camera‐based spectra recovery, the spectral reflectance of the object being imaged always needs to be accurately recovered using training samples from available database. Considering the heavy workload when using all samples in database as training samples in practice, a new representative samples selection method is proposed for effici...

A psychophysical experiment using 3D printed samples was conducted to investigate the change of perceived color differences caused by two different illuminations and two 3D sample shapes. 150 pairs of 3D printed samples around five CIE color centers [Color Res. Appl. 20, 399–403, 1995], consisting of 75 pairs of spherical samples and 75 pairs of fl...

A study by Gao et al found that the Newton method may not converge for certain combinations of the photopic luminance and the ratio of scotopic and photopic luminance for computing the adaptation coefficient m, for the CIE MES2 system for mesopic photometry. Hence, they proposed to use the Bisection‐Newton method. In this short note, we propose the...

We studied skin color in participants before and after a 100‐m sprint using a Konica Minolta CM‐2600d spectrophotometer. Four body positions (forehead, cheek, neck, and inner forearm) were measured for the approximately 30 students (non‐professional runners) who participated in the experiment. Skin reflectance was measured three times at each posit...

Experience and experimental results show that the perceived colour appearance of an object varies with the size of that object or the viewing angle. Based on available visual size‐effect data, it is found that the size effect can be compensated in the CAT16 cone‐like space. Furthermore, it is found that, similar to the von Kries chromatic adaptatio...

Accurate facial skin colour representation is highly required for an increasing number of applications, such as the solution of cosmetic products, the diagnosis of cutaneous diseases, and the manufacture of soft tissue prostheses. This study presents a novel camera colour characterisation model with higher predictive accuracy for the image-based co...

The main ingredient of sunless tanning products is dihydroxyacetone (DHA). DHA reacts with the protein and amino acid composition in the surface layers of the skin, producing melanoidins, which changes the skin colour, imitating natural skin tan caused by melanin. The purpose of this study was to characterise DHA-induced skin colour changes and to...

The main ingredient of sunless tanning products is dihydroxyacetone (DHA). DHA reacts with the protein and amino acid composition in the surface layers of the skin, producing melanoidins, which changes the skin colour, imitating natural skin tan caused by melanin. The purpose of this study was to characterise DHA-induced skin colour changes and to...

Digital camera-based spectral estimation in open environment is a challenge in current stage. Although some methods have been proposed in recent years, the methods do not consider the exposure inconsistency between camera spectral characterization and spectral estimation applications, that makes the proposed method cannot for practical applications...

This paper proposes a multi-spectral imaging system, developed using a commercial-grade camera, under two commonly used illumination. Rather than using conventional direct or diffuse light, the novelty of our method is to use a cross-polarized imaging system to eliminate glare and specular highlights. Two RGB images are captured under two different...

Various color difference metrics were developed for characterizing the perceived color difference between individual color patches. Color difference between palettes containing multiple color patches, however, is critically important in product design and computer graphics. This study aimed to investigate how the perceived color difference between...

Various color difference metrics were developed for characterizing the perceived color difference between individual color patches. Color difference between palettes containing multiple color patches, however, is critically important in product design and computer graphics. This study aimed to investigate how the perceived color difference between...

In this paper, skin tone heterogeneity in five facial areas (forehead, right cheekbone, left cheekbone, nose tip and chin) was investigated under six light sources with correlated color temperature (CCT) of 2850 K, 3500 K, 5000 K, 5500 K, 6500 K and 9000 K. Firstly, a facial image capturing protocol was developed and applied to five female particip...

We estimated Trump’s skin colour from 70 internet images and also from the “twitter tan line” image (February 8, 2020; Twitter). We then compared the estimated skin colours with two existing data sets of skin colours: the range of skin tans that occur naturally in the Caucasian population and the range skin colours brought about by a sunless tan. W...

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. Both the larger hue ang...

This work is concerned with the prediction of visual colour difference between pairs of palettes. In this study, the palettes contained five colours arranged in a horizontal row. A total of 95 pairs of palettes were rated for visual difference by 20 participants. The colour difference between the palettes was predicted using two algorithms, each ba...

Most viable modern chromatic adaptation transforms (CATs), such as CAT16 and CAT02, can trace their roots both conceptually and mathematically to a simple model formulated from the hypotheses of Johannes von Kries in 1902, known as von Kries transform/model. However, while the von Kries transform satisfies the properties of symmetry and transitivit...

In this paper, the current technologies for full-colour 3D printing are reviewed with a special focus on colour image reproduction frameworks using the 3DPTM and PolyJetTM printing engines. For each system, conventional cross-media colour management has been applied to transform the colours of real 3D objects from one medium (e.g. a 3D camera image...

Today, both additive manufacturing (3D image technology and 3D printing) had been developed dramatically and involved virtually in all fields of medicine and surgery. It has been widely applied in surgical and prosthetic reconstruction of the craniofacial defects. The aim of this chapter is to characterize and assess the mechanical and optical prop...

An improved spectral reflectance estimation method is developed to transform raw camera RGB responses to spectral reflectance. The novelty of our method is to apply a local weighted linear regression model for spectral reflectance estimation and construct the weighting matrix using a Gaussian function in CIELAB uniform color space. The proposed met...

Despite the importance of the appearance of human skin for theoretical and practical purposes, little is known about visual sensitivity to subtle skin-tone changes, and whether the human visual system is indeed optimized to discern skin-color changes that confer some evolutionary advantage. Here, we report discrimination thresholds in a three-dimen...

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 Duv (i.e., 0, −0.0...

Currently the fixed-point iteration method with initial guess m0=0.5 is officially recommended by the CIE MES2 system [CIE 191:2010] in order to compute the adaptation coefficient m and the mesopic luminance Lmes. However, recently, Gao et al. [Opt. Express25, 18365 (2017)] and Shpak et al. [Lighting Res. Technol.49, 111 (2017)] have numerically fo...

CAM16 colour appearance model has been extended to predict the appearance for stimulus of varying sizes and to provide new scales to evaluate saturation, vividness, whiteness and blackness.

Objectives: 3D colour printing, a method of additive manufacturing, has been developed and utilised to produce facial soft tissue prostheses. This was achieved by layered fabrication of a biocompatible powder held together by an aqueous binder containing a resin and coloured inks, followed by infiltration with a medical grade silicone polymer. The...

Recent progress in additive manufacturing technology has improved the realistic colour reproduction of 3D facial prostheses with computational optimisation of skin colour profiles. The colour appearance of the prosthetic surface depends on both the spectral characteristics of the surfaces and the scene illumination. Considering everyday environment...

Objective To provide an approach to facial contrast, analysing CIELAB colour differences (ΔE*ab,10) and its components in women's faces from two different ethnic groups, illuminated by modern white light‐emitting diodes (LEDs) or traditional illuminants recommended by the International Commission on Illumination (CIE). Methods We performed spectro...

This study aimed to investigate the variability of skin colour measurements for two kinds of extensively used instruments, telespectroradiometers (TSR) and spectrophotometers. A Konica Minolta CM700d spectrophotometer and a PhotoResearch PR650 telespectroradiometer were used to measure the forehead and the cheekbone of 11 subjects. The variability...

In our recent work, the colour preference of several LED white lights with different correlated colour temperatures (CCTs) was investigated with a wide selection of objects. The results highlighted the dominant effect of light itself on the colour preference of lighting. In this study, we similarly implemented two psychophysical experiments with th...

1st Museum Lighting Symposium

Skin color provides essential information about an individual's health condition and emotion. Additive manufacturing of human skin has been developed markedly in recent years along with increasing demands for clinical and medical applications. It is therefore critical to achieve precise color reproduction of facial skin and constant color appearanc...

New values of parameters a and b are proposed for the CIE system of mesopic photometry MES2 [CIE Publication 191:2010], because from the original values this model may have no solution or multi-solutions. From the new values of parameters a and b it is shown that the CIE MES2 system has a unique solution. The difference however, between the origina...

A novel metric named Gamut Volume Index (GVI) is proposed for evaluating the colour preference of lighting. This metric is based on the absolute gamut volume of optimized colour samples. The optimal colour set of the proposed metric was obtained by optimizing the weighted average correlation between the metric predictions and the subjective ratings...

Colour preference for lighting is generally influenced by three kinds of contextual factors, the light, the object and the observer. In this study, a series of psychophysical experiments were conducted to investigate and compare the effect of certain factors on colour preference, including spectral power distribution of light, lighting application,...

Skin color provides essential information about an individual’s health condition and emotion. Additive manufacturing of human skin has been developed markedly in recent years along with increasing demands for clinical and medical applications. It is therefore critical to achieve precise color reproduction of facial skin and constant color appearanc...

This paper focuses on human skin colour. Three different colour measuring instruments were used: a tele-spectroradiometer, a de:8o and a 45o:0o spectrophotometers. They were used to measure 47 subjects who were divided into four skin groups: Chinese, Caucasian, South-Asian and Dark. Eight locations for each subject were measured. The spectral refle...

Human skin colour information is important for the cosmetic industries and hospitals to develop a skin product and suggest an appropriate treatment. Human skin has multi-layered structures with non-flat surface and the colour of the human skin is unevenly distributed over the body. It is difficult to get skin colour information both exhaustively an...

Two experiments were conducted for collecting skin database at the Universities of Liverpool and Leeds (UK), and Zhejiang University (China). Overall, 235 subjects from 4 different skin groups (Caucasians, Chinese, South Asian and Dark) were recruited. Each was measured using 4 types of colour measuring methods (tele-spectroradiometer, spectrophoto...