A color gamut compression algorithm -Interactive gamut mapping experiment -Analysis of observer j... more A color gamut compression algorithm -Interactive gamut mapping experiment -Analysis of observer judgements The new algorithm -Preserve color relationships Constructing a core gamut Matching the local conformations Reversible manner -The new algorithm performed well
Objectives: 3D colour printing, a method of additive manufacturing, has been developed and utilis... more 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 aim of this study was to investigate the elastomer infiltration depths within the 3D printed models.
Objective: Skin colour measurement and analysis was performed for Iraqi Kurdish population in sul... more Objective: Skin colour measurement and analysis was performed for Iraqi Kurdish population in sulaimani city. The purpose of this study was to produce a dedicated skin shade guide for precise colour reproduction and colour matching of maxillofacial prostheses with the patient’s original skin colour. Methodology: A skin colour measurement was undertaken for 140 subjects (73 female and 67 male). A method of capturing their (L* a* b*) colour values from nine body parts was performed using a Minolta CM-2600d spectrophotometer and a colour Data Software. The study sample aged between 18 to 50 years from Sulaimani city representing a Kurdish population of the north of Iraq. A comparison was made between (L* a* b*) colour values of the face and arm and between male and female shades. Data analysed using Independent-samples T-Test. Furthermore this study aimed at employing the performed data for suggesting a dedicated skin shade guide for the population examined in this study. Results: A si...
Objectives: The purpose of this study was to establish a unique colour gamut for human skin in or... more Objectives: The purpose of this study was to establish a unique colour gamut for human skin in order to provide a basic guideline for developing a fully automated method of manufacturing soft tissue prostheses using advanced manufacturing technologies. Methods: Ethics approval was obtained from the University of Sheffield UREC to carry out this study on volunteers. A target was set to obtain direct colour measurements from 100 individuals from each of six ethnic groups. The measurements were conducted by using a CM 2600d spectrophotometer under standard D65 illuminant. Both CIE XYZ tristimulus values and spectral reflectance were measured for each subject for 9 different body positions on the face and arms. An advanced colour appearance model was adopted to predict human perceptual attributes for skin colour and a 3D colour gamut was constructed using a Segment Maxima GBD (SMGBD). Results: To date we have collected data for 49 Caucasians and the preliminary colour gamut for this eth...
Aim: To test the effect of UV light and weathering conditions on the mechanical properties and co... more Aim: To test the effect of UV light and weathering conditions on the mechanical properties and colour stability of a maxillofacial silicone polymer. Materials & Methods: Samples (n=6) for tensile strength, tear strength and hardness were manufactured from Sil-25 using customized stainless steel moulds designed according to ASTM specifications and tested using a tensile tester (Lloyd instruments LRX Mod.23), and hardness tester (Sure A Durometer 4478). Coloured silicone discs, representing 5 ethnic skin tones, were also fabricated using S/S moulds (25x6 mm). L*a*b* and ΔE were then measured using a Minolta spectrophotometer (CM-2600d). Properties were measured before and after exposure to UVL and weathering conditions in a Q-U-V accelerated weathering tester (ASTM G154) for 1 week and 6 weeks - equivalent to approximately 3 years and 18 years exposure in natural conditions respectively. Results: The average value of both the tensile and tear strength were significantly reduced after ...
A Chinese skin colour database is established based on measurements taken from nine bodies areas ... more A Chinese skin colour database is established based on measurements taken from nine bodies areas of 202 Chinese individuals to move towards accurate skin colour reproduction. The colour appearance of each skin point is predicted, and a comprehensive colour gamut for Chinese skin is determined. A consistent colour shift between facial and arm colours is identified, in which facial colour tends to be more reddish, more colourful, and darker than arm colour. Moreover, Chinese females are found to have lighter, paler, and more yellowish skin than Chinese males. Variations in Chinese skin colour are quantified, and body area differences and gender differences are shown to have significant effects on Chinese skin colour.
ABSTRACT A new 3D colour image reproduction system is proposed for automatic and accurate additiv... more ABSTRACT A new 3D colour image reproduction system is proposed for automatic and accurate additive manufacturing of facial prostheses. The general framework of colour image reproduction was defined and a protocol for each sub-process was developed for this specific application. Prototypes of both nose and ear prostheses were produced using the proposed system. The produced facial prostheses are capable of providing accurate shape, fine texture and improved colour reproduction, with significant savings in both time and cost.
ABSTRACT Principal component analyses (PCA) were conducted for skin spectral reflectance of a new... more ABSTRACT Principal component analyses (PCA) were conducted for skin spectral reflectance of a new skin colour database. Results for skin colours from different ethnic groups were analysed and reflectance re-construction based on first three components obtained by PCA were investigated. Significant differences in the derived principal components for the three ethnic groups were found. Furthermore, a new nonlinear optimization model based on all reflectance data was developed for generating the three basis functions for reflectance reconstruction. Comparison results for reflectance predictions show the basis functions obtained from the new optimisation model are better than those obtained from PCA.
Clromatic sensitivity along the protan, deutan, and tritan lines and the loci of the unique hues ... more Clromatic sensitivity along the protan, deutan, and tritan lines and the loci of the unique hues (red, green, yellow, blue) for a very large sample (n = 185) of colour-normal observers ranging from 18 to 75 years of age are assessed. Visual judgments are obtained under normal viewing conditions using colour patches on self-luminous display under controlled adaptation conditions. Trivector discrimination thresholds show an increase as a function of age along the protan, deutan, and tritan axes, with the largest increase present along the tritan line, less pronounced shifts in unique hue settings are also observed. Based on the chromatic (protan, deutan, tritan) thresholds and using scaled cone signals, we predict the unique hue changes with ageing. A dependency on age for unique red and unique yellow for predicted hue angle is found. We conclude that the chromatic sensitivity deteriorates significantly with age, whereas the appearance of unique hues is much less affected, remaining almost constant despite the known changes in the ocular media.
Observers are faster to detect a target among a set of distracters if the targets and distracters... more Observers are faster to detect a target among a set of distracters if the targets and distracters come from different color categories. This cross-boundary advantage seems to be limited to the right visual field, which is consistent with the dominance of the left hemisphere for language processing [Gilbert et al., Proc. Natl. Acad. Sci. USA 103, 489 (2006)]. Here we study whether a similar visual field advantage is found in the color identification task in speakers of Mandarin, a language that uses a logographic system. Forty late Mandarin–English bilinguals performed a blue–green color categorization task, in a blocked design, in their first language (L1: Mandarin) or second language (L2: English). Eleven color singletons ranging from blue to green were presented for 160 ms, randomly in the left visual field (LVF) or right visual field (RVF). Color boundary and reaction times (RTs) at the color boundary were estimated in L1 and L2, for both visual fields. We found that the color boundary did not differ between the languages; RTs at the color boundary, however, were on average more than 100 ms shorter in the English compared to the Mandarin sessions, but only when the stimuli were presented in the RVF. The finding may be explained by the script nature of the two languages: Mandarin logographic characters are analyzed visuospatially in the right hemisphere, which conceivably facilitates identification of color presented to the LVF.
Purpose. The purpose of this study was to assess in a large sample of adult colour-normal observe... more Purpose. The purpose of this study was to assess in a large sample of adult colour-normal observers of a wide age group (n=185; age range: 18-75) whether sensitivity changes due to ageing are associated with corresponding changes in the colour-opponent mechanisms that mediate hue perception. We therefore obtained the following data in the same set of observers: the sensitivity along the protan, deutan and tritan line and setting for the four unique hues from which the characteristics of the colour-opponent mechanisms can be derived. Results. We find a significant decrease in chromatic sensitivity with increasing age, in particular along the tritan line. When we predict the relative cone weights (L:S) of the colour-opponent mechanisms from the chromatic (protan, deutan, tritan) thresholds, we find a pronounced dependency on age. The observed relative cone weights (associated with a particular hue), on the other hand, are rather constant throughout the life span. Conclusion. The weighting of the cone inputs by the colour-opponent mechanisms (redgreen; yellow-blue) appears to change with age. Such an adaptive weighting with is useful to maintain colour constancy throughout the life span in the presence of known changes in the ocular media and retinal sensitivity losses.
An achromatic stimulus is defined as a patch of light that is devoid of any hue. This is usually ... more An achromatic stimulus is defined as a patch of light that is devoid of any hue. This is usually achieved by asking observers to adjust the stimulus such that it looks neither red nor green and at the same time neither yellow nor blue. Despite the theoretical and practical importance of the achromatic locus, little is known about the variability in these settings. The main purpose of the current study was to evaluate whether achromatic settings were dependent on the task of the observers, namely the navigation direction in color space. Observers could either adjust the test patch along the two chromatic axes in the CIE u*v* diagram or, alternatively, navigate along the unique-hue lines. Our main result is that the navigation method affects the reliability of these achromatic settings. Observers are able to make more reliable achromatic settings when adjusting the test patch along the directions defined by the four unique hues as opposed to navigating along the main axes in the commonly used CIE u*v* chromaticity plane. This result holds across different ambient viewing conditions (Dark, Daylight, Cool White Fluorescent) and different test luminance levels (5, 20, and 50 cd/m 2 ). The reduced variability in the achromatic settings is consistent with the idea that internal color representations are more aligned with the unique-hue lines than the u* and v* axes.
Advanced manufacture 3D color printing a b s t r a c t Objectives: The objectives of this study w... more Advanced manufacture 3D color printing a b s t r a c t Objectives: The objectives of this study were to develop a color reproduction system in advanced manufacture technology for accurate and automatic processing of soft tissue prostheses.
An improved method for visual gamma correction is developed for LCD displays to increase the accu... more An improved method for visual gamma correction is developed for LCD displays to increase the accuracy of digital colour reproduction. Rather than utilising a photometric measurement device, we use observers' visual luminance judgements for gamma correction. Eight half tone patterns were designed to generate relative luminances from 1/9 to 8/9 for each colour channel. A psychophysical experiment was conducted on an LCD display to find the digital signals corresponding to each relative luminance by visually matching the half-tone background to a uniform colour patch. Both inter-and intra-observer variability for the eight luminance matches in each channel were assessed and the luminance matches proved to be consistent across observers (DE 00 < 3.5) and repeatable (DE 00 < 2.2). Based on the individual observer judgements, the display opto-electronic transfer function (OETF) was estimated by using either a 3rd order polynomial regression or linear interpolation for each colour channel. The performance of the proposed method is evaluated by predicting the CIE tristimulus values of a set of coloured patches (using the observer-based OETFs) and comparing them to the expected CIE tristimulus values (using the OETF obtained from spectro-radiometric luminance measurements). The resulting colour differences range from 2 to 4.6 DE 00 . We conclude that this observer-based method of visual gamma correction is useful to estimate the OETF for LCD displays. Its major advantage is that no particular functional relationship between digital inputs and luminance outputs has to be assumed.
A color gamut compression algorithm -Interactive gamut mapping experiment -Analysis of observer j... more A color gamut compression algorithm -Interactive gamut mapping experiment -Analysis of observer judgements The new algorithm -Preserve color relationships Constructing a core gamut Matching the local conformations Reversible manner -The new algorithm performed well
Objectives: 3D colour printing, a method of additive manufacturing, has been developed and utilis... more 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 aim of this study was to investigate the elastomer infiltration depths within the 3D printed models.
Objective: Skin colour measurement and analysis was performed for Iraqi Kurdish population in sul... more Objective: Skin colour measurement and analysis was performed for Iraqi Kurdish population in sulaimani city. The purpose of this study was to produce a dedicated skin shade guide for precise colour reproduction and colour matching of maxillofacial prostheses with the patient’s original skin colour. Methodology: A skin colour measurement was undertaken for 140 subjects (73 female and 67 male). A method of capturing their (L* a* b*) colour values from nine body parts was performed using a Minolta CM-2600d spectrophotometer and a colour Data Software. The study sample aged between 18 to 50 years from Sulaimani city representing a Kurdish population of the north of Iraq. A comparison was made between (L* a* b*) colour values of the face and arm and between male and female shades. Data analysed using Independent-samples T-Test. Furthermore this study aimed at employing the performed data for suggesting a dedicated skin shade guide for the population examined in this study. Results: A si...
Objectives: The purpose of this study was to establish a unique colour gamut for human skin in or... more Objectives: The purpose of this study was to establish a unique colour gamut for human skin in order to provide a basic guideline for developing a fully automated method of manufacturing soft tissue prostheses using advanced manufacturing technologies. Methods: Ethics approval was obtained from the University of Sheffield UREC to carry out this study on volunteers. A target was set to obtain direct colour measurements from 100 individuals from each of six ethnic groups. The measurements were conducted by using a CM 2600d spectrophotometer under standard D65 illuminant. Both CIE XYZ tristimulus values and spectral reflectance were measured for each subject for 9 different body positions on the face and arms. An advanced colour appearance model was adopted to predict human perceptual attributes for skin colour and a 3D colour gamut was constructed using a Segment Maxima GBD (SMGBD). Results: To date we have collected data for 49 Caucasians and the preliminary colour gamut for this eth...
Aim: To test the effect of UV light and weathering conditions on the mechanical properties and co... more Aim: To test the effect of UV light and weathering conditions on the mechanical properties and colour stability of a maxillofacial silicone polymer. Materials & Methods: Samples (n=6) for tensile strength, tear strength and hardness were manufactured from Sil-25 using customized stainless steel moulds designed according to ASTM specifications and tested using a tensile tester (Lloyd instruments LRX Mod.23), and hardness tester (Sure A Durometer 4478). Coloured silicone discs, representing 5 ethnic skin tones, were also fabricated using S/S moulds (25x6 mm). L*a*b* and ΔE were then measured using a Minolta spectrophotometer (CM-2600d). Properties were measured before and after exposure to UVL and weathering conditions in a Q-U-V accelerated weathering tester (ASTM G154) for 1 week and 6 weeks - equivalent to approximately 3 years and 18 years exposure in natural conditions respectively. Results: The average value of both the tensile and tear strength were significantly reduced after ...
A Chinese skin colour database is established based on measurements taken from nine bodies areas ... more A Chinese skin colour database is established based on measurements taken from nine bodies areas of 202 Chinese individuals to move towards accurate skin colour reproduction. The colour appearance of each skin point is predicted, and a comprehensive colour gamut for Chinese skin is determined. A consistent colour shift between facial and arm colours is identified, in which facial colour tends to be more reddish, more colourful, and darker than arm colour. Moreover, Chinese females are found to have lighter, paler, and more yellowish skin than Chinese males. Variations in Chinese skin colour are quantified, and body area differences and gender differences are shown to have significant effects on Chinese skin colour.
ABSTRACT A new 3D colour image reproduction system is proposed for automatic and accurate additiv... more ABSTRACT A new 3D colour image reproduction system is proposed for automatic and accurate additive manufacturing of facial prostheses. The general framework of colour image reproduction was defined and a protocol for each sub-process was developed for this specific application. Prototypes of both nose and ear prostheses were produced using the proposed system. The produced facial prostheses are capable of providing accurate shape, fine texture and improved colour reproduction, with significant savings in both time and cost.
ABSTRACT Principal component analyses (PCA) were conducted for skin spectral reflectance of a new... more ABSTRACT Principal component analyses (PCA) were conducted for skin spectral reflectance of a new skin colour database. Results for skin colours from different ethnic groups were analysed and reflectance re-construction based on first three components obtained by PCA were investigated. Significant differences in the derived principal components for the three ethnic groups were found. Furthermore, a new nonlinear optimization model based on all reflectance data was developed for generating the three basis functions for reflectance reconstruction. Comparison results for reflectance predictions show the basis functions obtained from the new optimisation model are better than those obtained from PCA.
Clromatic sensitivity along the protan, deutan, and tritan lines and the loci of the unique hues ... more Clromatic sensitivity along the protan, deutan, and tritan lines and the loci of the unique hues (red, green, yellow, blue) for a very large sample (n = 185) of colour-normal observers ranging from 18 to 75 years of age are assessed. Visual judgments are obtained under normal viewing conditions using colour patches on self-luminous display under controlled adaptation conditions. Trivector discrimination thresholds show an increase as a function of age along the protan, deutan, and tritan axes, with the largest increase present along the tritan line, less pronounced shifts in unique hue settings are also observed. Based on the chromatic (protan, deutan, tritan) thresholds and using scaled cone signals, we predict the unique hue changes with ageing. A dependency on age for unique red and unique yellow for predicted hue angle is found. We conclude that the chromatic sensitivity deteriorates significantly with age, whereas the appearance of unique hues is much less affected, remaining almost constant despite the known changes in the ocular media.
Observers are faster to detect a target among a set of distracters if the targets and distracters... more Observers are faster to detect a target among a set of distracters if the targets and distracters come from different color categories. This cross-boundary advantage seems to be limited to the right visual field, which is consistent with the dominance of the left hemisphere for language processing [Gilbert et al., Proc. Natl. Acad. Sci. USA 103, 489 (2006)]. Here we study whether a similar visual field advantage is found in the color identification task in speakers of Mandarin, a language that uses a logographic system. Forty late Mandarin–English bilinguals performed a blue–green color categorization task, in a blocked design, in their first language (L1: Mandarin) or second language (L2: English). Eleven color singletons ranging from blue to green were presented for 160 ms, randomly in the left visual field (LVF) or right visual field (RVF). Color boundary and reaction times (RTs) at the color boundary were estimated in L1 and L2, for both visual fields. We found that the color boundary did not differ between the languages; RTs at the color boundary, however, were on average more than 100 ms shorter in the English compared to the Mandarin sessions, but only when the stimuli were presented in the RVF. The finding may be explained by the script nature of the two languages: Mandarin logographic characters are analyzed visuospatially in the right hemisphere, which conceivably facilitates identification of color presented to the LVF.
Purpose. The purpose of this study was to assess in a large sample of adult colour-normal observe... more Purpose. The purpose of this study was to assess in a large sample of adult colour-normal observers of a wide age group (n=185; age range: 18-75) whether sensitivity changes due to ageing are associated with corresponding changes in the colour-opponent mechanisms that mediate hue perception. We therefore obtained the following data in the same set of observers: the sensitivity along the protan, deutan and tritan line and setting for the four unique hues from which the characteristics of the colour-opponent mechanisms can be derived. Results. We find a significant decrease in chromatic sensitivity with increasing age, in particular along the tritan line. When we predict the relative cone weights (L:S) of the colour-opponent mechanisms from the chromatic (protan, deutan, tritan) thresholds, we find a pronounced dependency on age. The observed relative cone weights (associated with a particular hue), on the other hand, are rather constant throughout the life span. Conclusion. The weighting of the cone inputs by the colour-opponent mechanisms (redgreen; yellow-blue) appears to change with age. Such an adaptive weighting with is useful to maintain colour constancy throughout the life span in the presence of known changes in the ocular media and retinal sensitivity losses.
An achromatic stimulus is defined as a patch of light that is devoid of any hue. This is usually ... more An achromatic stimulus is defined as a patch of light that is devoid of any hue. This is usually achieved by asking observers to adjust the stimulus such that it looks neither red nor green and at the same time neither yellow nor blue. Despite the theoretical and practical importance of the achromatic locus, little is known about the variability in these settings. The main purpose of the current study was to evaluate whether achromatic settings were dependent on the task of the observers, namely the navigation direction in color space. Observers could either adjust the test patch along the two chromatic axes in the CIE u*v* diagram or, alternatively, navigate along the unique-hue lines. Our main result is that the navigation method affects the reliability of these achromatic settings. Observers are able to make more reliable achromatic settings when adjusting the test patch along the directions defined by the four unique hues as opposed to navigating along the main axes in the commonly used CIE u*v* chromaticity plane. This result holds across different ambient viewing conditions (Dark, Daylight, Cool White Fluorescent) and different test luminance levels (5, 20, and 50 cd/m 2 ). The reduced variability in the achromatic settings is consistent with the idea that internal color representations are more aligned with the unique-hue lines than the u* and v* axes.
Advanced manufacture 3D color printing a b s t r a c t Objectives: The objectives of this study w... more Advanced manufacture 3D color printing a b s t r a c t Objectives: The objectives of this study were to develop a color reproduction system in advanced manufacture technology for accurate and automatic processing of soft tissue prostheses.
An improved method for visual gamma correction is developed for LCD displays to increase the accu... more An improved method for visual gamma correction is developed for LCD displays to increase the accuracy of digital colour reproduction. Rather than utilising a photometric measurement device, we use observers' visual luminance judgements for gamma correction. Eight half tone patterns were designed to generate relative luminances from 1/9 to 8/9 for each colour channel. A psychophysical experiment was conducted on an LCD display to find the digital signals corresponding to each relative luminance by visually matching the half-tone background to a uniform colour patch. Both inter-and intra-observer variability for the eight luminance matches in each channel were assessed and the luminance matches proved to be consistent across observers (DE 00 < 3.5) and repeatable (DE 00 < 2.2). Based on the individual observer judgements, the display opto-electronic transfer function (OETF) was estimated by using either a 3rd order polynomial regression or linear interpolation for each colour channel. The performance of the proposed method is evaluated by predicting the CIE tristimulus values of a set of coloured patches (using the observer-based OETFs) and comparing them to the expected CIE tristimulus values (using the OETF obtained from spectro-radiometric luminance measurements). The resulting colour differences range from 2 to 4.6 DE 00 . We conclude that this observer-based method of visual gamma correction is useful to estimate the OETF for LCD displays. Its major advantage is that no particular functional relationship between digital inputs and luminance outputs has to be assumed.
Uploads
Papers by Kaida Xiao