Skin color analysis using a spectrophotometer in Asians

Background/purpose: To objectively describe skin color, the Commission International d'Eclairage (CIE) L^*a^*b^* color coordinates and melanin and erythema indexes are used. However, it was difficult to understand the relationship among these parameters and to convert them into each other. We introduced a new technique to measure L^*a^*b^* color coordinates and the melanin and erythema indexes at the same time. We analyzed the skin color of normal Asians using this method. Methods: The skin color of the forehead, cheek, upper inner arm, dorsum of hand, and anterior chest of 148 volunteers was measured using a spectrophotometer. Using a computer analysis program, L^*a^*b^* values and the melanin and erythema indexes were presented at the same time. The averages of these data were shown according to gender, age, body parts, and correlations among the melanin and erythema indexes and L^*a^*b^* color coordinates, and then they were analyzed. Results: The averages of the melanin and erythema indexes of 148 participants were 1.10 ± 0.29 and 1.29 ± 0.38, respectively. The averages of the L^*, a^*, and b^* values were 64.15 ± 4.86, 8.96 ± 2.65, and 18.34 ± 2.39, respectively. The melanin and erythema indexes were higher in males than in females. While the correlation of the melanin index with the L^* value was negative, it was positively correlated with the a^* and b^* values. While the erythema index showed a weak correlation with the b^* value, its correlation was negative with the L^* value and positive with the a^* value. Conclusion: Our method of skin color measurement is useful. We consider the data of this study valuable basic data for the evaluation of colors of pigmental skin diseases and scars in the future.     

Skin color measurements: comparison between three instruments: the Chromameter®, the DermaSpectrometer® and the Mexameter®

Background/aims: Two types of skin reflectance instruments are available nowadays for the determination of skin color: a tristumulus colorimeter (Chromameter from Minolta) using the CIE L*a*b* color system and the narrow‐band simple reflectance meters (DermaSpectrometer from Cortex and Mexameter from Courage‐Khazaka) using the erythema/melanin indices. The purpose of this study was to compare the capabilities of the three instruments (sensitivity, repeatability and correlation) in vitro and in vivo. Methods: Comparative color measurements were carried out first in vitro on standardized color charts and subsequently in vivo on different skin areas in human volunteers. Skin color changes induced by various physico‐chemical treatments were also quantitatively evaluated with the three instruments. Results: The in vitro and in vivo repeatabilty as well as the sensitivity of the three instruments are rather good. Erythema and skin blanching could be readily quantified by the increase of the a* parameter and of the erythema indices of the simple reflectance meters. Natural UV tanning and artificial chemical tanning could be measured by the decrease of L* and increase of b* and of the melanin indices. Conclusion: The Chromameter and the two narrow‐band reflectance instruments were able to characterize skin color and to quantify small skin color changes. Moderate to high significant linear correlations could be established between the CIE L*a*b* color parameters and the erythema/melanin indices.     

The Visi-Chroma VC-100®: a new imaging colorimeter for dermatocosmetic research

Background/aims: It was the aim of this study to carry out a comparative evaluation in vitro on standardized color charts and in vivo on healthy subjects using the Visi‐Chroma VC‐100^®, a new imaging tristimulus colorimeter and the Minolta Chromameter CR‐200^® as a reference instrument. The Visi‐Chroma combines tristimulus color analysis with full color visualization of the skin area measured. The technical performances of both instruments were compared with the purpose of validating the use of this new imaging colorimeter in dermatocosmetic research. Methods: In vitro L*a*b* color parameters were taken with both instruments on standardized color charts (Macbeth and RAL charts) in order to evaluate accuracy, sensitivity range and repeatability. These measurements were completed by in vivo studies on different sites of human skin and studies of color changes induced by topical chemical agents on forearm skin. The accuracy, sensitivity range and repeatability of measurements of selected distances and surfaces in the measuring zone considered and specific color determinations of specific skin zones were also determined. Results: The technical performance of this imaging colorimeter was rather good, with low coefficients of variation for repeatability of in vitro and vivo color measurements. High positive correlations were established in vitro and in vivo over a wide range of color measurements. The imaging colorimeter was able to measure the L*a*b* color parameters of specific chosen parts of the skin area considered and to measure accurately selected distances and surfaces in the same skin site considered. Conclusion: These comparative measurements show that both instruments have very similar technical performances and that high levels of correlation were obtained in vitro and in vivo using the L*a*b* color parameters. In addition, the Visi‐Chroma presents the following improvements: 1) direct visualization and recording of the skin area considered with concomitant color measurements; 2) determination of the specific color parameters of skin areas chosen in the total measuring area; and 3) accurate determination of selected distances and surfaces in the same skin areas chosen.     

Graphic analysis of the relationship between skin colour change and variations in the amounts of melanin and haemoglobin

Background/aims The L*a*b* coordinate is the most commonly used colour system to measure skin colour in dermatology and cosmetology. In this system, a* and L* are often used for quantification of the degrees of erythema and pigmentation. The aim of this study was to examine whether a* and L* can be used as specific scales to indicate the amount of haemoglobin and melanin, respectively, in the skin.
Methods The a* and L* values were examined with a reflectance spectrometer in various skin conditions or lesions caused by a change in the amount of either melanin or haemoglobin, i.e. vitiligo, ultraviolet-induced pigmentation (PG), erythema resulting from slapping (ER), corticosteroid-induced blanching, erythema due to stasis by arm lowering, and a combination of PG and ER. The differences in values between the test sites and the adjacent normal skin, Δa* and ΔL*, were plotted on the Δa*–ΔL* plane and analysed statistically and geometrically.
Results L* depended substantially not only on melanin but also on haemoglobin, especially if the oxygen saturation level was expected to be low. a* was also influenced by melanin. The results of graphic analysis indicated that a linear transformation of (Δa*, ΔL*) into (ΔHb = 1.68 Δa* + 0.60 ΔL*, ΔMel =−1.06 Δa*–1.44 ΔL*) was suitable for separately estimating the change in the amount of haemoglobin (ΔHb) and in that of melanin (ΔMel).
Conclusion The results of this study may be of value for understanding the relationship between colour coordinates of the skin and the quantities of haemoglobin and melanin, and may be of use when pigmented lesions of the face are monitored by tristimulus colourimetry, as facial skin colour is affected considerably by the rich and easily variable cutaneous blood flow.     

Change of biophysical properties of the skin caused by ultraviolet radiation-induced photodamage in Koreans.

BACKGROUND/PURPOSE: Ultraviolet (UV) irradiation affects the function and complexion of the skin by inducing changes in physical properties through formation of erythema, proliferation of epithelial cells, DNA damage, activation or inactivation of various enzymes and proteins, and free radical formation. In this study, the authors intended to observe the overall course of changes in barrier function and reflectance of the skin induced by photodamage, and healing reaction in the course of time, and alteration of the skin complexion. METHODS: The subjects were chosen from 15 healthy Korean men 20-35 in age, that fall into the category of Fitzpatrick's skin types II, III, and IV without history of recent exposure to sunlight, photosensitivity, or having taken any drugs that induce phototoxicity or photoallergic reactions. The subjects were artificially exposed to suberythemogenic dose [0.5 minimal erythemal dose (MED), 0.75 MED], 1 MED and high dose (2.5 MED) by solar simulator, and changes in skin barrier function and skin reflectance were assessed with a Tewameter, a Corneometer, and a Colorimeter for 4 weeks. RESULTS: Transepidermal water loss (TEWL) increased abruptly at Day 1 of single solar UV (SSUV) exposure, and slowly returned to the original level from Day 2/Day 3. In the case of exposure with 0.75 MED, it returned to the original level at Day 4 of exposure, and at Days 7 and 28 in the cases of 1 MED and 2.5 MED exposure, respectively. Water-holding capacity sharply declined at Day 1 of exposure, hitting the lowest point at Day 2, and then slowly recovered starting on Day 3. In the case of exposure with 0.75 MED and 1 MED, it returned to the original level at Days 7 and 28 in the case of 2.5 MED exposure. The a(*) values abruptly increased and reached the peak at Day 1 and slowly returned to the original level at Day 2, while the b(*) values slowly increased at Day 3, peaking at Day 7 and slowly returning to the original level thereafter. The L(*) values abruptly declined at Day 1, maintaining plateau through Day 7 and slowly returning to the baseline level thereafter. The individual typology angle (ITA degrees ) were compatible with L(*) values change. The erythema index increased abruptly at Day 1 of SSUV exposure, peaking at Day 2 and slowly returned to the original level starting at Day 3. Melanin index slowly started to increase on Day 3 of SSUV exposure, peaking at Day 7 and gradually returned to the original level thereafter. However, L(*), a(*), b(*), erythema index, and melanin index did not return to the original level during the 28-day course of this study. CONCLUSION: This study shows that in the skin of Korean subjects, changes in skin barrier function and delayed melanization do occur even in exposure to a suberythemogenic dose of SSUV. Also, given the fact that restoration of barrier function occurs as the process of melanization begins, melanization is considered to be a useful predictive indicator of the restoration of the skin barrier function after sunburn.     

Relationship between constitutive skin color and ultraviolet light sensitivity in Koreans

The assessment of skin sensitivity to ultraviolet (UV) radiation is important in treating a variety of skin diseases and preventing the deleterious effects of UV. Although there are many ways to predict the sensitivity to UVR, controversies exist over their objectivity, correlation, and applicability in various races. For the purpose of evaluating the relationship of skin color and UV responsiveness, this study was performed to assess the validity of constitutive skin color for an individual's UV sensitivity in 80 healthy Korean volunteers. The subjects were divided into two groups: a young-aged group with 40 subjects aged 20-39 years and an old-aged group with 40 subjects aged 43-63 years. A minimal erythema dose (MED) of UVB and minimal immediate pigment darkening dose (MIPDD) of UVA were assessed using a fluorescent lamp (Panasol II, National Biologic Co., Twinberg, USA) and a metal-halide lamp (Dermalight 2001, Mutzhas, Munich, Germany), respectively. The constitutive skin color of buttock was measured with a Minolta Chroma Meter CR-300 (Osaka, Japan), using the CIE (Commission International de l'Eclairege) L*a*b* system. Of the three L*a*b*, we used the L* value to estimate the skin color. For the MED and L* values, the values were inversely proportionate (P<0.05) in the young-aged group; however, no correlation existed in the old-aged group. No relationships existed among Fitzpatrick skin type and MED, skin type and MIPDD. The results of this study indicated that the constitutive skin colors in the young-aged group can be an objective and adequate predictor of cutaneous UV sensitivity.     

Skin reflectance-spectra and colour-value dependency on measuring-head aperture area in ordinary reflectance spectrophotometry and tristimulus colourimetry

Background/aims:   Measurement of skin colour has become increasingly popular in the study of dermatology with the increased availability of portable instruments. However, different instruments have been reported as giving different results from measurement of the same skin region. The aim of this study was to examine the effects of differences in measuring-head aperture area on skin reflectance spectra and colour values.
Methods:   We measured both reflectance spectra and CIE-L*a*b* values of the skin in five different anatomical regions on 10 subjects using two MINOLTA reflectance spectrometers that were identical apart from the aperture area of the measuring heads (diameters: 5 and 11 mm). For comparison, data were also obtained from a skin-coloured tile.
Results:   Skin reflectance values measured with the wider-aperture instrument were higher than those measured with the other, irrespective of anatomical location. The differences between the two were near zero at an incident light wavelength of 400 nm, but increased to around 10% of the reflectance value at 700 nm, increasing exponentially with incident light of increasing wavelength. Skin colour was observed to be brighter, redder and yellower, in CIE-L*a*b* expression, when measured with the wider-aperture instrument. The differences between measurements obtained from the skin-coloured tile were much smaller.
Conclusion:   Skin reflectance and colour values measured with reflectance instruments are not absolute data but depend on the aperture area of the measuring head. This is probably due to variations in the proportion of longer-wavelength light reflected from the skin and collected by the instrument.     

New approach to the evaluation of skin color of pigmentary lesions using Skin Tone Color Scale

Objective methods of measuring skin color are needed to evaluate pigmentary lesions quantitatively. We have developed a new method of measuring skin color using a plastic bar system called the Skin Tone Color Scale based on Munsell's color space system. We have also evaluated the effectiveness of various therapies using this measurement system. Our system was designed to measure skin color in normal skin, pigmentary lesions of solar lentigo, chloasma and ephelides, and postinflammatory pigmentation. Moreover, effectiveness of various therapies for these pigmentary lesions was evaluated. The evaluations made with this system were closely related to physician assessment. This method may be useful in measuring of skin color and evaluating the effectiveness of therapies for pigmentary diseases.     

Skin lesion classification using relative color features

BACKGROUND/PURPOSE: Clinically, it is difficult to differentiate the early stage of malignant melanoma and certain benign skin lesions due to similarity in appearance. Our research uses image analysis of clinical skin images and relative color-based pattern recognition techniques to enhance the images and improve differentiation of these lesions. METHODS: First, the relative color images were created from digitized photographic images. Then, they were segmented into objects and morphologically filtered. Next, the relative color features were extracted from the objects to form two different feature spaces; a lesion feature space and an object feature space. The two feature spaces serve as two data models to be analyzed to determine the best features. Finally, we used a statistical analysis model of relative color features, which better classifies the various types of skin lesions. RESULTS/CONCLUSIONS: The best features found for differentiation of melanoma and benign skin lesions from this study are area, mean in the red and blue bands, standard deviation in the red and green bands, skewness in the green band, and entropy in the red band. With the relative color feature algorithm developed, the best results were obtained with a multi-layer perceptron neural network model. This showed an overall classification success of 79%, with 70% of the benign lesions successfully classified, and 86% of malignant melanoma successfully classified.     

Topographic measurement of skin color by narrow-band reflectance spectrophotometer and minimal erythema dose (MED) in Koreans

Background/aims: Narrow-band reflectance spectrophotometer is one of the objective and quantitative devices for measuring the skin colors. There has been some controversy concerning the relationship between the objectively measured skin color and cutaneous responsiveness to ultraviolet radiation, including minimal erythema dose (MED). The aims of this study were to compare the color of Korean brown skin with that of Caucasians by objective measurement with the narrow-band reflectance spectrophotometer, and to determine whether the skin color has any correlation with MED in Koreans, and demonstrate differences in this correlation according to the anatomical sites. Methods: With narrow-band reflectance spectrometer, skin colors were measured at 17 body sites of 20 healthy Korean male volunteers after measuring MED for the same subjects. Results: The constitutional skin color, as measured by the melanin index of the nonexposed sites, showed a statistically significant correlation with MED values, whereas the facultative skin color did not. The Korean brown skin showed higher melanin index and lower erythema index compared with that of Caucasians. Conclusions: We confirmed significant differences in the correlation between MED and melanin indices, depending on the anatomic sites. This suggests that selection from various sites, even among the nonexposed sites, is quite important and deserves further evaluation.