RESUMEN

Observer metamerism (OM) is the name given to the variability between the color matches that individual observers consider accurate. The standard color imaging approach, which uses color-matching functions of a single representative observer, does not accurately represent every individual observer's perceptual properties. This paper investigates OM in color displays and proposes a quantitative assessment of the OM distribution across the chromaticity diagram. An OM metric is calculated from a database of individual LMS cone fundamentals and the spectral power distributions of the display's primaries. Additionally, a visualization method is suggested to map the distribution of OM across the display's color gamut. Through numerical assessment of OM using two distinct publicly available sets of individual observers' functions, the influence of the selected dataset on the intensity and distribution of OM has been underscored. The case study of digital cinema has been investigated, specifically the transition from xenon-arc to laser projectors. The resulting heatmaps represent the "topography" of OM for both types of projectors. The paper also presents color difference values, showing that achromatic highlights could be particularly prone to disagreements between observers in laser-based cinema theaters. Overall, this study provides valuable resources for display manufacturers and researchers, offering insights into observer metamerism and facilitating the development of improved display technologies.

RESUMEN

Accurate color reproduction is highly important in multiple industrial, biomedical and scientific applications. Versatile and tunable light sources with high color-rendering quality are very much in demand. In this study, we demonstrate the feasibility of multi-wavelength Bragg diffraction of light for this task. Tuning the frequencies and amplitudes of bulk acoustic waves in the birefringent crystal demonstrates high precision in setting the number, wavelengths and intensities of the monochromatic components necessary to reproduce a specific color assigned according to its coordinates in the CIE XYZ 1931 space. We assembled a setup based on multi-bandpass acousto-optic (AO) filtration of white light and verified the reproduced color balance in multiple experiments. The proposed approach delivers almost full coverage of the CIE XYZ 1931 space and facilitates building compact color reproduction systems (CRSs) for various purposes.

RESUMEN

Color 3D printing has been widely used in many fields such as cultural, medical, industrial, and food. The color reproduction accuracy of 3D printed products in these fields is becoming increasingly demanding, which requires more reproduction methods and practical tools. At present, most color 3D printing devices use one quantitative index, that is, color difference, to directly predict the color reproduction quality. However, this single quantitative index is not optimal for the curved surface of 3D printed color objects. Based on color evaluation principles, in this study, five new quantitative metrics consisting of color gamut comparison index, color SSIM index, color FSIM index, iCID index, and subjective scaling values are proposed for comparison, and the corresponding GUI design and code implementation of new color quality evaluation system are performed by MATLAB. Moreover, the comprehensive color assessment of color 3D printed products is confirmed by utilizing standard image acquisition and microscopic imaging methods that are not limited to printing materials and sampling locations. The operation of this system is validated to provide interactivity, simplicity and high efficiency. As a result, the system can provide new valuable feedback for color separation and output calibration of color 3D printing devices.

RESUMEN

A visual and easy-to-implement representation approach of red wine color is proposed in this work. The wine color under standard conditions, called feature color, was reproduced in the form of a circular spot. The feature color was further decomposed into two orthogonal aspects, the chromatic and light-dark components, characterized in the form of chromaticity distribution plane and lightness distribution plane, respectively. The color characterization of wine samples showed that this method well represented the color characteristics and can provide intuitive visual perception of wine color, in a way that is more reliable and convenient than the photographic method. The applications for monitoring the color evolution during winery and laboratory fermentation and the age discrimination of 175 commercial red wines suggest that this visual method is effective for color management and control of wine during fermentation and aging. The proposed method is a convenient way to present, store, convey, understand, analyze and compare the color information of wines.

RESUMEN

Spectral reflectance reconstruction for multispectral images (such as Weiner estimation) may perform sub-optimally when the object being measured has a texture that is not in the training set. The accuracy of the reconstruction is significantly lower without training samples. We propose an improved reflectance reconstruction method based on L1-norm penalization to solve this issue. Using L1-norm, our method can provide the transformation matrix with the favorable sparse property, which can help to achieve better results when measuring the unseen samples. We verify the proposed method by reconstructing spectral reflection for four types of materials (cotton, paper, polyester, and nylon) captured by a multispectral imaging system. Each of the materials has its texture and there are 204 samples in each of the materials/textures in the experiments. The experimental results show that when the texture is not included in the training dataset, L1-norm can achieve better results compared with existing methods using colorimetric measure (i.e., color difference) and shows consistent accuracy across four kinds of materials.

Asunto(s)

RESUMEN

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 color in the CIELab* color space, we propose a practical framework, HPCAPR, for skin facial reflectance reconstruction based on calibrated datasets which reconstruct the facial spectra in subsets derived from clustering techniques in several spectrometric and colorimetric spaces, i.e., the spectral reflectance space, Principal Component (PC) space, CIELab*, and its three 2D subordinate color spaces, La*, Lb*, and ab*. The spectra reconstruction algorithm is optimized by combining state-of-art algorithms and thoroughly scanning the parameters. The results show that the hybrid of PCA and RGB polynomial regression algorithm with 3PCs plus 1st-order polynomial extension gives the best results. The performance can be improved substantially by operating the spectral reconstruction framework within the subset classified in the La* color subspace. Comparing with not conducting the clustering technique, it attains values of 25.2% and 57.1% for the median and maximum errors for the best cluster, respectively; for the worst, the maximum error was reduced by 42.2%.

Asunto(s)

RESUMEN

El objetivo de este estudio fue valorar las estrategias empleadas, por estudiantes de la Facultad de Odon-tología de la Universidad de Buenos Aires para la re-producción del color en restauraciones del sector anterior según autorreporte. Materiales y Métodos: Se confeccionó un formulario en Google Forms (F) que los alumnos completaron en sus celulares con la información correspondiente a cada restaura-ción terminada. Resultados (IC95%): Se registraron 97 restauraciones en el sector anterior. El 57,73 % (47,79 - 67,09) proximales no involucraban el ángu-lo incisal y el 21,65 % (14,62 - 30,84) sí. Un 11,34 % (6,45 - 19,17) localizada en el tercio cervical. En el 93,81 % (87,15 - 97,13) se utilizó al menos una capa de composite de opacidad esmalte (E) mientras que en el 77,32 % (68,04 - 84,52) al menos una de dentina (D). En el 73,19 % (63,63 - 81,01) se utilizaron al me-nos dos opacidades E y D. Los colores de E más utili-zados fueron A2 y A3, 31,87 % (23,19 - 42,01) y 37,36 % (28,12 - 47,62) respectivamente, y el A3 de D 54,67 % (43,45 - 65,43). Tres fueron las estrategias princi-pales para la combinación de colores y opacidades: el empleo de colores iguales en ambas opacidades, y el uso de opacos de mayor o de menor intensidad; entre las que no se encontró ninguna predominante. Conclusiones: A partir de los resultados del presente estudio se puede concluir que en la mayoría de las restauraciones del sector anterior se emplean com-posites de al menos dos opacidades y que no hay una estrategia de asociación de opacidad y color predominante (AU)

The aim of this study was to assess the strategies that students from the Facultad de Odontología, Universidad de Buenos Aires claim to use for color reproduction in anterior restorations. Materials and Methods: A form was created in Google Forms (F) and students were instructed to complete on 40REV FAC ODONTOL, UNIV BUENOS AIRES 2023 VOL 38 N° 90RepRoducción del coloR en RestauRaciones del sectoR anteRioRFosas y fisurasProximales sin compromiso de ánguloProximales con compromiso de ánguloTercio cervicalcaras libres706050403020100% (IC95%)57,73%21,65%11,34%9,28%their cell phones with the corresponding information about each completed restoration. Results(95CI%):97 restorations were recorded in the anterior sector of which 57.73 % (47.79 - 67.09) were proximal and 21.65 % (14.62 - 30.84) that involved the incisal edge.11.34 %(6.45 - 19.17) were located in the cervical third of the vestibular surfaces. In 97.94 % of the restorations Brilliant New Generation (Coltene) the chosen composite, in 93.81 % (87.15 - 97.13) enamel opacity composite (E) was used at least for one layer, while in 77.32 % (68. 04 - 84.52) at least one layer of dentin (D) was applied. In 73.19 % (63.63 - 81.01) at least two opacities E and D were required. The most used E shades were A2 and A3, 31.87 % (23.19 - 42, 01) and 37.36 % (28.12 - 47.62) respectively, and A3 of D shades 54.67 % (43.45 - 65.43). Three core strategies were identified: the use of the same colors in both opacities, and the use of opaque of greater or lesser intensity; among which no predominance was found. Conclusions: Within the conditions of this study, it can be concluded that composites of at least two opacities are used in most anterior sector restorations and that there is no predominant opacity and color association strategy (AU)

Asunto(s)

RESUMEN

Color 3D printing has widely affected our daily lives; therefore, its precise control is essential for aesthetics and performance. In this study, four unique test plates were printed using powder-based full-color 3D printing as an example; moreover, the corresponding pigment-penetration depth, chromaticity value and image-based metrics were measured to investigate the lateral pigment penetration characteristics and relative surface-color reproduction of each color patch, and to perform an objective analysis with specific microscopic images. The results show that the lateral pigment-penetration depth correlates with the number of printed layers on the designed 3D test plates, and the qualitative analysis of microscopic images can explain the change in chromaticity well. Meanwhile, there is an obvious linear correlation between the mean structural similarity, color-image difference and color difference for current color samples. Thus, our proposed approach has a good practicality for powder-based color 3D printing, and can provide new insight into predicting the color-presentation efficiency of color 3D-printed substrates by the abovementioned objective metrics.

RESUMEN

Sunlight has participated in the development of all life forms on Earth. The micro-world and the daily rhythms of plants and animals are strongly regulated by the light-dark rhythm. Human beings have followed this pattern for thousands of years. The discovery and development of artificial light sources eliminated the workings of this physiological clock. The world's current external environment is full of light pollution. In many electrical light bulbs used today and considered "environmentally friendly," such as LED devices, electrical energy is converted into short-wavelength illumination that we have not experienced in the past. Such illumination effectively becomes "biological light pollution" and disrupts our pineal melatonin production. The suppression of melatonin at night alters our circadian rhythms (biological rhythms with a periodicity of 24 h). This alteration is known as chronodisruption and is associated with numerous diseases. In this article, we present a blue-free WLED (white light-emitting diode) that can avoid chronodisruption and preserve circadian rhythms. This WLED also maintains the spectral quality of light measured through parameters such as CRI (color reproduction index).

Asunto(s)

RESUMEN

We developed a system to improve the quality of telemedicine, and the test results obtained have been presented in this paper, along with the technical details of the system. The spread of COVID-19 has accelerated the need for telemedicine to effectively prevent infections. However, in traditional Japanese medicine (Kampo), where color is essential, an accurate diagnosis cannot be made without color reproduction. Because commercial smartphones cannot reproduce colors with the level of fidelity required for medical treatments, we created a color chart that includes the human skin and tongue colors to help doctors identify their colors accurately during a telemedicine examination. Further, we developed a telemedicine system that allows for automatic color correction using a mobile device, with a color chart and non-contact heart rate measurements.

RESUMEN

In this paper, we propose a color reproduction method using color charts to improve the color quality of a telemedicine system. Owing to the spread of COVID-19, the need for telemedicine is rapidly increasing to prevent infections more effectively. However, in practices such as traditional Japanese (Kampo) medicine, where color is used as an important examination factor, an accurate diagnosis cannot be made without adequate color reproduction. In telemedicine using a commercially available smartphone, color reproducibility may deteriorate owing to differences in the devices and lighting, which may result in a misdiagnosis. Therefore, we created a color chart that includes the colors of the human skin and tongue as a tool to help doctors identify the color of patients more accurately when conducting a telemedicine examination. Through a subjective evaluation by eight medical doctors, it was unanimously found that the proposed method is practical in terms of a color examination. The developed color chart can also be used for an automatic color correction.

RESUMEN

Color three-dimensional (3D) printing is an advanced 3D printing technique for reproducing colorful 3D objects, but it still has color accuracy issues. Plastic-based color 3D printing is a common color 3D printing process, and most factors affecting its color reproduction quality have been studied from printing materials to parameters in the fixed consecutive layers. In this work, and combined with variable stair thickness, the colored layer sequence in sliced layers of a specific 3D color test chart is deliberately changed to test the effects of colored layer features on its final color reproduction quality. Meanwhile, the colorimetric measurement and image acquisition of printed 3D color test charts are both achieved under standard conditions. Results clearly show that the chromatic aberration values and mean structural similarity (MSSIM) values of color samples have a significant correlation with the colored stair thickness, but both did not display a linear relationship. The correlation trends between colored layer sequence and the above two indexes are more localized to the colored stair thickness. Combined with color structural similarity (SSIM) maps analysis, a comprehensive discussion between colored layer features and color reproduction quality of color 3D printing is presented, providing key insights for developing further accurate numerical models.

Asunto(s)

RESUMEN

Previous research has shown that the effectiveness of selecting filter sets from among a large set of commercial broadband filters by a vector analysis method based on maximum linear independence (MLI). However, the traditional MLI approach is suboptimal due to the need to predefine the first filter of the selected filter set to be the maximum ℓ2 norm among all available filters. An exhaustive imaging simulation with every single filter serving as the first filter is conducted to investigate the features of the most competent filter set. From the simulation, the characteristics of the most competent filter set are discovered. Besides minimization of the condition number, the geometric features of the best-performed filter set comprise a distinct transmittance peak along the wavelength axis of the first filter, a generally uniform distribution for the peaks of the filters and substantial overlaps of the transmittance curves of the adjacent filters. Therefore, the best-performed filter sets can be recognized intuitively by simple vector analysis and just a few experimental verifications. A practical two-step framework for selecting optimal filter set is recommended, which guarantees a significant enhancement of the performance of the systems. This work should be useful for optimizing the spectral sensitivity of broadband multispectral imaging sensors.

RESUMEN

In this paper, we present a real-time preprocessing algorithm for image enhancement for endoscopic images. A novel dictionary based color mapping algorithm is used for reproducing the color information from a theme image. The theme image is selected from a nearby anatomical location. A database of color endoscopy image for different location is prepared for this purpose. The color map is dynamic as its contents change with the change of the theme image. This method is used on low contrast grayscale white light images and raw narrow band images to highlight the vascular and mucosa structures and to colorize the images. It can also be applied to enhance the tone of color images. The statistic visual representation and universal image quality measures show that the proposed method can highlight the mucosa structure compared to other methods. The color similarity has been verified using Delta E color difference, structure similarity index, mean structure similarity index and structure and hue similarity. The color enhancement was measured using color enhancement factor that shows considerable improvements. The proposed algorithm has low and linear time complexity, which results in higher execution speed than other related works.

RESUMEN

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. METHODS: The manufacturing protocol was defined to effectively and consistently produce soft tissue prostheses using a 3D printing system. Within this protocol printer color profiles were developed using a number of mathematical models for the proposed 3D color printing system based on 240 training colors. On this basis, the color reproduction system was established and their system errors including accuracy of color reproduction, performance of color repeatability and color gamut were evaluated using 14 known human skin shades. RESULTS: The printer color profile developed using the third-order polynomial regression based on least-square fitting provided the best model performance. The results demonstrated that by using the proposed color reproduction system, 14 different skin colors could be reproduced and excellent color reproduction performance achieved. Evaluation of the system's color repeatability revealed a demonstrable system error and this highlighted the need for regular evaluation. The color gamut for the proposed 3D printing system was simulated and it was demonstrated that the vast majority of skin colors can be reproduced with the exception of extreme dark or light skin color shades. CONCLUSIONS: This study demonstrated that the proposed color reproduction system can be effectively used to reproduce a range of human skin colors for application in advanced manufacture of soft tissue prostheses.

Asunto(s)

RESUMEN

Objective: To study the color reproduction ratio of metal ceramic restoration in clinic. Methods:The color of 150 maxillary incisors and its metal ceramic restorations was measured by MinoltCR 321 chromaticity instrument(D65 daylight simulator inside),the color reproduction ratio was calculated with CIE 1976 L*a*b* system. Results: The color reproduction ratio of metal ceramic restoration measured by clinical eye evaluation was 33.9%.Color error ratio was 66.1%. Conclusion: The color reproduction ratio measured by eye evaluation is low and the color error ratio is high.