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In colour industry it is really important to know the colour gamut of a device. Through the comparison of gamuts we can see the effects that the use of different inks, papers, light sources or printing technologies has on the colour obtained. There are several programs that make this comparison, but they have some drawbacks. Therefore, we have developed and validated a software to compare colour gamuts generated by printing devices. Before doing so, we have selected the most suitable procedure to carry out this comparison. The software, programmed in MATLAB, represents the gamuts simultaneously in the 3D CIELAB space by interpolating the most external data of the gamut. It also calculates their volume using two algorithms: Convex Hull and Alpha Shapes. The representation is made by interacting with the buttons on the interface. To validate our software, we have performed a double analysis. On the one hand, we have compared the results obtained from the study of the colour gamuts with our software and those obtained in a previous work with the same data. On the other hand, we have used the program ICC3D to compare the representations of the gamuts superimposed in 3D with those of our program, in addition to the volume obtained. The conclusions obtained after using the two programs were the same. Even so, our program presents some advantages. It allowed us to identify differences between the gamuts that were not discriminated by other methods, obtaining more precise information. The new software will allow the study and comparison of gamuts generated by different printing technologies with different papers, ICC profiles and light sources. RESUMEN. En la industria del color es muy importante conocer la gama de colores de un dispositivo. Mediante la comparación de gamas podemos evaluar el efecto que tiene el uso de distintas tintas, papeles, fuentes de iluminación o dispositivos de impresión en el color obtenido. Existen diversos programas que realizan esta comparación, pero tienen inconvenientes. Por ello hemos desarrollado y validado un software para comparar gamas de color generadas por dispositivos de impresión gráfica. Antes de ello, hemos seleccionado el procedimiento más adecuado para realizar esta comparación. El software, programado en MATLAB, representa las gamas simultáneamente en el espacio 3D CIELAB a partir de la interpolación de los datos más externos de la gama, además de calcular su volumen mediante dos algoritmos: Convex Hull y Alpha Shapes. La representación se realiza a partir de la interacción con los botones de la interfaz. Para validar nuestro software hemos realizado un doble análisis. Por un lado, hemos comparado los resultados obtenidos del estudio de las gamas de color con nuestro software y los obtenidos en un TFG previo con los mismos datos. Por otro lado, hemos usado el programa ICC3D para comparar las representaciones de las gamas superpuestas en 3D con las de nuestro programa, además del volumen obtenido. Las conclusiones tras el uso de los dos programas fueron las mismas, encontrando figuras muy similares. Aun así, nuestro programa presenta algunas ventajas. Este nos permitió distinguir diferencias entre las gamas que mediante otros métodos no se discriminaron, obteniendo información más precisa. El nuevo software va a permitir el estudio y comparación de las gamas generadas por distintos dispositivos de impresión gráfica con distintos sustratos de impresión, perfiles ICC e iluminación.

When an array of LEDs has to be repaired in or removed from a traffic light, it is necessary interrupt traffic. A lift has to elevate workers to the traffic-light disks, entailing job-safety dangers, high costs, and traffic disruption. To allay some of these problems, we have designed a new illumination system with LEDs, using minilenses set into the base of the traffic light, from which a bundle of optical fibers emerge to feed the disks, and these optical fibers transport the light from the array of LEDs to the disks. The new traffic lights will improve traffic and worker safety because the repairs are made on the ground.

When a LED array needs to be replaced or a traffic light needs repair, the traffic in one lane must be interrupted and lifts are needed to elevate the repairman, with all the danger that this involves, in addition to the economic cost and the traffic disruption caused. We have designed an illumination system for a traffic-light model in which the LED array is located at the base of the traffic light and from this emerges a bundle of optical fibers connected to the illumination plate of the traffic light. We seek to improve traffic safety and possibly achieve lower costs.

Charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) matrices offer excellent features in imaging systems. For assessing the suitability of each technology according to the application, the complete characterization of the detector arrays becomes necessary. A system is optically characterized by the modulation transfer function (MTF). We have comparatively studied the results provided by the speckle method for detectors of two types: CCD and CMOS. To do so, we first analysed the precision in determining the MTF of the CCD using two apertures at the exit port of an integrating sphere: a single and a double-slit. For the single-slit, we propose a new procedure of fitting the experimental data which overcomes the drawbacks of the conventional procedure. Since it offered lower uncertainty and better reproducibility, the single-slit was used for the study with the CMOS detector. Significant differences were found between the MTF of the CCD and the CMOS detectors.

An intensity-based fiber-optic liquid-level gauge for continuous measurement is described. The sensing principle is based on the total internal reflection of light within the fiber optic, and for this, a measurement is made of the power attenuation which occurs in the fiber optic immersed in the liquid tank when the liquid level varies. The light from a LED is modulated before being directed into the fiber to minimize measurement errors. The device contains an alarm programmable to signal any liquid level in the tank (high or low), and data can be sent via Internet in real time to a distant point.

Age-related changes in tooth color have been described previously, however, the use of dental color for age estimation in forensic odontology has been limited due to the difficulty of measuring color objectively. This study presents an objective method for determining dental color to estimate the age of an individual. Dentine color in 250 teeth from patients ranging in age from 10 to 89 years was determined by spectroradiometry. Color measurements were performed as suggested in the CIE 1931 (International Commission on Illumination). Chromaticity coordinates (x, y, z), luminance (Y), whiteness index (WIC, Z%, WIC) and yellowness index (YI) were obtained. Correlations between these colorimetric variables and aging were established by linear regression analyses. All the variables fit the mathematical model with correlation coefficients ranging from 0.53 to 0.75. This method of color measurement produced an expected associated error of calibration averaging 13.7 years about the mean estimated values, at a 70% level of confidence. Two different multiple regression models for dental age estimation were tested, and variables that made the greatest contributions to age calculation were identified. To determine the effect of postmortem interval on tooth color and its influence in age estimation, 37 teeth obtained from human skeletal remains buried during an interval ranging from 21 to 37 years were also studied. In this material, the correlation between age and dental color measured by spectroradiometry was weaker than in fresh extracted teeth. It is concluded that determination of dentine color by spectroradiometry is a potentially useful objective method to estimate age in forensic studies in combination with other methods.

In this work, we present a low-cost experimental setup to evaluate the image quality of digital-camera sensors, which can be implemented in undergraduate and postgraduate teaching. The method consists of evaluating the modulation transfer function (MTF) of digital-camera sensors by speckle patterns using a ping-pong ball as a diffuser, with two handmade circular apertures acting as input and output ports, respectively. To specify the spatial-frequency content of the speckle pattern, it is necessary to use an aperture; for this, we made a slit in a piece of black cardboard. First, the MTF of a digital-camera sensor was calculated using the ping-pong ball and the handmade slit, and then the MTF was calculated using an integrating sphere and a high-quality steel slit. Finally, the results achieved with both experimental setups were compared, showing a similar MTF in both cases

In this work, we present a teaching methodology using active-learning techniques in the course “Devices and Instrumentation” of the Erasmus Mundus Master's Degree in “Color in Informatics and Media Technology” (CIMET). A part of the course “Devices and Instrumentation” of this Master's is dedicated to the study of image sensors and methods to evaluate their image quality. The teaching methodology that we present consists of incorporating practical activities during the traditional lectures. One of the innovative aspects of this teaching methodology is that students apply the concepts and methods studied in class to real devices. For this, students use their own digital cameras, webcams, or cellphone cameras in class. These activities provide students a better understanding of the theoretical subject given in class and encourage the active participation of students.

The present work examines the relationship between random-dot stereograms (via the disparity range parameter) and color-vision mechanisms (via the luminance channel and red-green and tritan directions at isoluminance). The results clearly indicate that the variations in the stereograms along red-green confusion lines contribute to stereopsis. Stereoscopic perception depends on spatial information for stereograms generated with variations along tritan confusion lines. For observers who perceive stereopsis via tritan directions, the results show a gradation in the disparity range, with the disparity range for stereograms generated by luminance variations being greater than for stereograms generated in red-green directions; the latter range is, in turn, greater than for stereograms generated along tritan directions. © 1997 Elsevier Science Ltd. All rights reserved

An analysis has been made of the stability of the images generated by electronic autostereoscopic 3D displays, studying the time course of the photometric and colorimetric parameters. The measurements were made on the basis of the procedure recommended in the European guideline EN 61747-6 for the characterization of electronic liquid-crystal displays (LCD). The study uses 3 different models of autostereoscopic 3D displays of different sizes and numbers of pixels, taking the measurements with a spectroradiometer (model PR-670 SpectraScan of PhotoResearch). For each of the displays, the time course is shown for the tristimulus values and the chromaticity coordinates in the XYZ CIE 1931 system and values from the time periods required to reach stable values of these parameters are presented. For the analysis of how the procedure recommended in the guideline EN 61747-6 for 2D displays influenced the results, and for the adaption of the procedure to the characterization of 3D displays, the experimental conditions of the standard procedure were varied, making the stability analysis in the two ocular channels (RE and LE) of the 3D mode and comparing the results with those corresponding to the 2D. The results of our study show that the stabilization time of a autostereoscopic 3D display with parallax barrier technology depends on the tristimulus value analysed (X, Y, Z) as well as on the presentation mode (2D, 3D); furthermore, it was found that whether the 3D mode is used depends on the ocular channel evaluated (RE, LE).

Surface properties are essential for a complete characterization of biomaterials. In restorative dentistry, the study of the surface properties of materials meant to replace dental tissues in an irreversibly diseased tooth is important to avoid harmful changes in future treatments. We have experimentally analyzed the surface characterization parameters of two different types of dental-resin composites and pre-sintered and sintered zirconia ceramics. We studied two shades of both composite types and two sintered zirconia ceramics: colored and uncolored. Moreover, a surface treatment was applied to one specimen of each dental-resin. All the samples were submitted to rugometric and microtopographic non-invasive inspection with the MICROTOP.06.MFC laser microtopographer in order to gather meaningful statistical parameters such as the average roughness (Ra), the root-mean-square deviation (Rq), the skewness (Rsk), and the kurtosis of the surface height distribution (Rku). For a comparison of the different biomaterials, the uncertainties associated to the surface parameters were also determined. With respect to Ra and Rq, significant differences between the composite shades were found. Among the dental resins, the nanocomposite presented the highest values and, for the zirconia ceramics, the pre-sintered sample registered the lowest ones. The composite performance may have been due to clusterformation variations. Except for the composites with the surface treatment, the sample surfaces had approximately a normal distribution of heights. The surface treatment applied to the composites increased the average roughness and moved the height distribution farther away from the normal distribution. The zirconia-sintering process resulted in higher average roughness without affecting the height distribution., This research is supported by Grant MAT2009-09795 from the Spanish Ministry of Science and Innovation. A. Fernandez-Oliveras is recipient of a FPU PhD Scholarship from the Spanish Ministry of Science and Innovation.

Light propagation in biological media is characterized by the absorption coefficient, the scattering coefficient, the scattering phase function, the refractive index, and the surface conditions (roughness). By means of the inverse-adding-doubling (IAD) method, transmittance and reflectance measurements lead to the determination of the absorption coefficient and the reduced scattering coefficient. The additional measurement of the phase function performed by goniometry allows the separation of the reduced scattering coefficient into the scattering coefficient and the scattering anisotropy factor. The majority of techniques, such as the one utilized in this work, involve the use of integrating spheres to measure total transmission and reflection. We have employed an integrating sphere setup to measure the total transmittance and reflectance of dental biomaterials used in restorative dentistry. Dental biomaterials are meant to replace dental tissues, such as enamel and dentine, in irreversibly diseased teeth. In previous works we performed goniometric measurements in order to evaluate the scattering anisotropy factor for these kinds of materials. In the present work we have used the IAD method to combine the measurements performed using the integrating sphere setup with the results of the previous goniometric measurements. The aim was to optically characterize the dental biomaterials analyzed, since whole studies to assess the appropriate material properties are required in medical applications. In this context, complete optical characterizations play an important role in achieving the fulfillment of optimal quality and the final success of dental biomaterials used in restorative dentistry.

Spectroradiometric measurements have been made for the experimental characterization of the RGB channels of autostereoscopic 3D displays, giving results for different measurement angles with respect to the normal direction of the plane of the display. In the study, 2 different models of autostereoscopic 3D displays of different sizes and resolutions were used, making measurements with a spectroradiometer (model PR-670 SpectraScan of PhotoResearch). From the measurements made, goniometric results were recorded for luminance contrast, and the fundamental hypotheses have been evaluated for the characterization of the displays: independence of the RGB channels and their constancy. The results show that the display with the lower angle variability in the contrast-ratio value and constancy of the chromaticity coordinates nevertheless presented the greatest additivity deviations with the measurement angle. For both displays, when the parameters evaluated were taken into account, lower angle variability consistently resulted in the 2D mode than in the 3D mode.

In dental applications, optimizing appearance is desirable and increasingly demanded by patients. The specular gloss is among the major appearance properties of dental biomaterials, and its relationship with surface roughness has been reported. Roughness and gloss are key surface aspects that complement each other. We have experimentally analyzed the specular gloss and surface roughness of two different types of dental-resin composites and pre-sintered and sintered zirconia ceramics. We have studied two shades of both composite types and two sintered zirconia ceramics: colored and uncolored. Moreover, a surface treatment was applied to one specimen of each dental resin. Gloss measurements were performed with a standardized reflectometer and the corresponding gloss percentages were calculated. All the samples were submitted to rugometric non-invasive inspection with the MICROTOP.06.MFC laser microtopographer in order to determine meaningful statistical parameters such as the average roughness (Ra) and the root-mean-square deviation (Rq). For a comparison of the different biomaterials, the uncertainties associated to the measure of the surface gloss and roughness were also determined. The differences between the two shades of both kinds of composites proved significant in the case of the roughness parameters but not for the specular gloss. The surface treatment applied to the dental-resin composites increased the average roughness but the changes in the specular gloss were significant only for the A2 enamel nano-composite. For the zirconia ceramic the sintered process resulted in an increase in the surface roughness with a decrease of the specular gloss, corroborating that the relationship between the gloss and the roughness shows the expected behavior., This research is supported by Grant MAT2009-09795 from the Spanish Ministry of Science and Innovation. A. Fernandez-Oliveras is recipient of a FPU PhD Scholarship from the Spanish Ministry of Science and Innovation.

The physical understanding of the optical properties of dental biomaterials is mandatory for their final success in restorative applications.Light propagation in biological media is characterized by the absorption coefficient, the scattering coefficient, the scattering phase function,the refractive index, and the surface conditions (roughness). We have employed the inverse adding-doubling (IAD) method to combine transmittanceand reflectance measurements performed using an integrating-sphere setup with the results of the previous scattering-anisotropygoniometric measurements. This has led to the determination of the absorption and the scattering coefficients. The aim was to opticallycharacterize two different dental-resin composites (nanocomposite and hybrid) and one type of zirconia ceramic, and comparatively studythem. The experimental procedure was conducted under repeatability conditions of measurement in order to determine the uncertaintyassociated to the optical properties of the biomaterials. Spectral variations of the refraction index and the scattering anisotropy factor werealso considered. The whole experimental procedure fulfilled all the necessary requirements to provide optical-property values with lowerassociated uncertainties. The effective transport coefficient presented a similar spectral behavior for the two composites but completelydifferent for the zirconia ceramic. The results demonstrated that the scattering anisotropy exerted a clearly distinct impact on the opticalproperties of the zirconia ceramic compared with those of the dental-resin composites.

The results obtained by different authors show that when a color stimulus changes in both luminance and chromaticity, the visual reaction time (VRT) of an observer in detecting this chromatic change depends on nothing more than the luminance change and is regulated by Pieron's law. In the present work, we evaluate the VRT needed by an observer to detect the chromaticity difference between an adapting and variable stimulus. For this, we have used the experimental method of hue substitution, which allows us to maintain the luminance channel constant and thereby study the temporal response to changes only in chromaticity. The experiments were carried out with a CRT color monitor and the experimental results are expressed in different color-representation systems. The systems UCS-CIE 1964 (U*, V*, W*) and CIELUV show good correlations between the VRT and the chromaticity difference expressed in these systems, adjusting the VRT to an expression following Pieron's law: VRT-VRTon=k( Delta E)- beta .

This work describes a new device that enables the photometric evaluation of an observer's visual field by measuring the luminance distribution. To provide an example of the applications, we have obtained the equivalent veiling luminance for different directions of the observer's line of vision. The results enable us to compare different luminous environments from direct measurements, without having to resort to theoretical methods. © 1996

To determine the prevalence of myopia in the adult populations of two different ethnic communities in the Ecuadorian Amazon.Refraction with retinoscopy after cycloplegia was performed for 507 Naporuna (an ethnic group indigenous to the jungles of the Ecuadorian Amazon) and for 776 settlers (white-mestizos from the Andes, now living in the Amazon and working for the petroleum industry). Ages ranged from 18 to 45 years. All subjects had little or no formal education.The prevalence of myopia was 4.7% among the Naporuna and 5.5% among the settlers; the prevalence of hyperopia was higher, at 17.8% and 36.0%, respectively.The prevalence of myopia in the two communities studied agrees with the results of other studies showing a low prevalence of myopia among groups with low levels of formal education or groups living a nonurban lifestyle.

PURPOSE: To analyze the theoretical effect that pupil size, optical zone, and initial myopic level have on the final retinal image after corneal refractive surgery. METHODS: A schematic myopic eye model corrected by the Munnerlyn formula was used to analyze the optical quality of the final retinal image. Root-mean-square radius spot and modulation transfer function were calculated by ray tracing to evaluate retinal image quality. RESULTS: Pupil size had a negative effect on the retinal image only when it was greater than the diameter of the optical zone. In addition, the greater the initial myopic level, the more the pupil size affected image quality. Thus, a clear dependence exists between the initial myopic level and effect that the pupil size can have on the retinal image after laser refractive surgery. CONCLUSIONS: Pupil size may be a risk factor for night vision disturbances, but only when it is larger than the theoretical optical zones utilized in this study. Its effect depends not only on the optical zone size, but also on the initial myopic level. Therefore, this relationship should be taken into account during patient selection for refractive surgery.

To calibrate a CRT color monitor, several assumptions are often made about its performance, one of the most accepted being constanel channel chromaticity. However, when the measurements are taken in a extended field of CRT screen, where it is assumed that only one primary phosphor is excited, the relative spectral radiance of the other primary phosphors that are contained in that field also contributes, if the background luminance is not zero. This contribution is greater at low levels of RGB channel stimulation and would invalidate the results obtained with calibration methods based on the hypothesis of constancy of chromaticity coordinates of RGB channels. We have studied this effect on the calibration of the CRT color monitor and, as a result, we propose a calibration that takes this effect into account. to evaluate the accuracy of the method, we have calculated color differences between the chromaticity that we wanted to reproduce and the one displayed with the CIELUV color-difference formula, and the color tolerances with the line element of MacAdam ellipses.

The influence of color signals on stereopsis has been studied using figural-stimuli stereograms with variations introduced according to the opponent chromatic channels (red-green and yellow-blue), derived from Boynton's color-vision model. We used wallpaper stereograms, which enable the rank-order disparity ranges of the chromatic and luminance signals to be compared with the rank-order disparity range of proximity, a particular spatial configuration of the stereogram in which there are no variations in chromaticity and/or luminance. The results indicate that both chromatic signals contribute to stereopsis as does the luminance signal, contradicting the model of Hubel and Livingstone. The results also show there are no clear dependencies upon the kind of signal processed, as luminance and chromatic variations are processed with the same efficiency.

In recent years, the flat-panel display (FPD) technology has undergone great development. Currently, FPDs are present in many devices. A significant element in FPD manufacturing is the display front surface. Manufacturers sell FPDs with different types of front surface which can be matte (also called anti-glare) or glossy screens. Users who prefer glossy screens consider images shown in these types of displays to have more vivid colours compared with matte-screen displays. However, external light sources may cause unpleasant reflections on the glossy screens. These reflections can be reduced by a matte treatment in the front surface of FPDs. In this work, we present a method to characterize the front surface of FPDs using laser speckle patterns. We characterized three FPDs: a Samsung XL2370 LCD monitor of 23" with matte screen, a Toshiba Satellite A100 laptop of 15.4" with glossy screen, and a Papyre electronic book reader. The results show great differences in speckle contrast values for the three screens characterized and, therefore, this work shows the feasibility of this method for characterizing and comparing FPDs which have different types of front surfaces

Today, video cameras connected to frame grabbers or video capture cards (VCCs) are used in many applications such as traffic control, surveillance, medical systems or machine vision. In this work, we present a method for determining the spatial-frequency response of VCCs. This method is based on the modulation transfer function (MTF) determination from speckle patterns using a low-cost experimental setup. We have evaluated and compared three different VCCs. The three VCCs produce an amplification (boost) in the horizontal MTF in a different spatial-frequency range, also differing in the maximum amplification value

Understanding the behaviour of light propagation in biological materials is essential for biomedical engineering and its applications. Among the key optical properties of biological media is the angular distribution of the scattered light, characterized by the average cosine of the scattering angle, called the scattering anisotropy coefficient (g). The value of g can be determined by experimentally irradiating the material with a laser beam and making angular-scattering measurements in a goniometer. In this work, an experimental technique was used to determine g by means of goniometric measurements of the laser light scattered off two different dental-resin composites (classified as nano and hybrid). To assess the accuracy of the experimental method, a Mie theory-based computational model was used. Independent measurements were used to determine some of the required input parameters for computation of the theoretical model. The g values estimated with the computational method (nano-filled: 0.9399; hybrid: 0.8975) and the values calculated with the experimental method presented (nano-filled: 0.98297 ± 0.00021; hybrid: 0.95429 ± 0.00014) agreed well for both dental resins, with slightly higher experimental values. The higher experimental values may indicate that the scattering particle causes more narrow-angle scattering than does a perfect sphere of equal volume, assuming that with more spherical scattering particles the scattering anisotropy coefficient increases. Since g represents the angular distribution of the scattered light, values provided by both the experimental and the computational methods show a strongly forward-directed scattering in the dental resins studied, more pronounced in the nano-filled composite than in the hybrid composite.

Knowledge of the optical properties of biological structures is useful for clinical applications, especially when dealing with incoming biomaterials engineered to improve the benefits for the patient. One ceramic material currently used in restorative dentistry is yttrium cation-doped tetragonal zirconia polycrystal (3Y-TZP) because of its good mechanical properties. However, its optical properties have not been thoroughly studied. Many methods for the determination of optical parameters from biological media make the assumption that scattered light is isotropically distributed over all angles. Nevertheless, real biological materials may have an angular dependence on light scattering, which may affect the optical behaviour of the materials. Therefore, the recovery of the degree of anisotropy in the scattering angular distribution is important. The phase function that represents the scattering angular distribution is usually characterized by the anisotropy coefficient g, which equals the average cosine of the scattering angle. In this work, we measured angularscattering distributions for two zirconia ceramic samples, pre-sintered and sintered, with similar thicknesses (0.48 mm and 0.50 mm, respectively) and also for a human dentine sample (0.41 mm in thickness). The samples were irradiated with a He-Ne laser beam (λ = 632.8 nm) and the angular-scattering distributions were measured using a rotating goniometer. The g values yielded were: -0.7970 ± 0.0016 for pre-sintered zirconia, -0.2074 ± 0.0024 for sintered zirconia and 0.0620 ± 0.0010 for dentine. The results show that zirconia sintering results in optical behaviour more similar to those of dentine tissue, in terms of scattering anisotropy.

Understanding the behaviour of light propagation in biological materials is essential for biomedical engineering and applications, and even more so when dealing with incoming biomaterials. Many methods for determining optical parameters from biological media assume that scattered light is isotropically distributed over all angles. However, an angular dependence of light scattering may exist and affect the optical behaviour of biological media. The present work seeks to experimentally analyze the scattering anisotropy in different dental tissues (enamel and dentine) and their potential substitute biomaterials (hybrid dental-resin, nano-filled composite, and zirconia ceramic) and comparatively study them. Goniometric measurements were made for four wavelengths in the visible range, allowing a spectral characterization of the materials studied. Previously, for each material, measurements were made with two different sample thicknesses at the same wavelength, checking the behaviour of the angular scattering profile. The asymmetry of experimental phase functions was considered in the recovery of the scattering anisotropy factor. The results demonstrate that the thicker sample yielded a less forward-directed scattering profile than did the thinner sample. The biomaterials analysed show angular scattering comparable to those of the tissues that they may replace. Comparisons can be made by virtue of the low uncertainties found.

Charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) matrices offer excellent features in imaging systems. A suitability evaluation of either technology according to a specific application requires a complete characterization of the different detector types. A system is optically characterized by the modulation transfer function (MTF), which represents its response in spatial frequency of this system. One of the methods to measure the MTF uses a laser speckle pattern as the object. Here, we comparatively examine the results provided by the speckle method to determine the MTF for detectors of two types: CCD and CMOS. We generate the speckle pattern using a laser and an integrating sphere with an aperture at its exit port. The aperture determined the spatial-frequency content of the pattern registered in the detector. The precision in determining the MTF of the CCD was studied using two different apertures: a single-slit and a double-slit. For the single-slit, we propose a new procedure of fitting the experimental data which resolves the drawbacks of the conventional procedure. To study the CMOS detector, we used the single-slit because it offered lower uncertainty and better reproducibility. The differences between the MTF values of the CCD and the CMOS detectors proved significant for the spatial frequencies higher than 50 cycles/mm, which is half of the interval studied with both arrays. For these spatial frequencies, our results demonstrate that the CCD detector presented MTF values higher than those of the CMOS array.

Since biological tissues can have the intrinsic property of altering the polarization of incident light, optical polarization studies are important for a complete characterization. We have measured the polarized light scattered off of different dental tissues and biomaterials for a comparative study of their optical polarization property. The experimental setup was composed by a He-Ne laser, two linear polarizers and a detection system based on a photodiode. The laser beam was passed through one linear polarizer placed in front of the sample, beyond which the second linear polarizer (analyzer) and the photodiode detector were placed. First, the maximum laser-light intensity (reference condition) was attained without the sample in the laser path. Then, the sample was placed between the two polarizers and the polarization shift of the scattered laser light was determined by rotating the analyzer until the reference condition was reached. Two dental-resin composites (nanocomposite and hybrid) and two human dental tissues (enamel and dentine) were analyzed under repeatability conditions at three different locations on the sample: 20 measurements of the shift were taken and the average value and the uncertainty associated were calculated. For the human dentine the average value of the polarization shift found was 7 degrees, with an associated uncertainty of 2 degrees. For the human enamel and both dental-resin composites the average shift values were found to be similar to their corresponding uncertainties (2 degrees). The results suggest that although human dentine has notable polarization properties, dental-resin composites and human enamel do not show significant polarization shifts.

We present and evaluate two corrections applicable in determining the modulation transfer function (MTF) of a charge-coupled device (CCD) by the speckle method that minimize its uncertainty: one for the low frequency region and another for the high frequency region. The correction at the low-spatial-frequency region enables attenuation of the high power-spectral-density values that arise from the field and CCD response non-uniformities. In the high-spatial-frequency region the results show that the distance between the CCD and the aperture is critical and significantly influences the MTF; a variation of 1 mm in the distance can cause a root-mean-square error in the MTF higher than 10%. We propose a simple correction that minimizes the experimental error committed in positioning the CCD and that diminishes the error to 0.43%., The authors express their appreciation to the Ministerio de Ciencia y Tecnología for financing projects FIS2004-06465-C02-01 and FIS2004-06465-C02-02.

A method is presented for measuring the modulation transfer function of ophthalmic lenses by use of the generation of laser speckle with an integrating sphere. The measurements are performed with a rectangular double-slit aperture positioned at the output port of the integrating sphere. The distance between the lens and the detector determines the spatial frequency being tested; therefore high frequencies are tested close to the lens and low frequencies are tested far away from the lens. We can conclude that the double-slit method can be a versatile technique for comparing the optical quality of ophthalmic lenses from different makers.

Two methods for measuring the modulation transfer function (MTF) of a charge-coupled device (CCD) that are based on the generation of laser speckle are analyzed and compared. The method based on a single-slit aperture is a quick method, although the measurements are limited to values of less than the Nyquist frequency of the device. The double-slit method permits the measurement of values of as much as some 1.8 times the Nyquist frequency, although it is a slower method because of the necessity to move the CCD. The difference between the MTF values obtained with the two methods is less than 0.1 in magnitude; the root-mean-square error between the two curves is 0.046 (4.6%).

The effect that decentered spectacle (ophthalmic) lenses exert on depth perception has been studied, evaluating stereopsis through the disparity range (maximum horizontal disparity) for random-dot stereograms (RDS). The results show that variations in fusional convergence due to increments of decentration can diminish the stereopsis in observers, reducing the region within which stereoscopic correspondence can take place. Decreases in disparity ranges were found for vertical and horizontal prismatic effects, although the prismatic effect necessary for this was less in the vertical case. A decreased disparity range has also been confirmed with figural-stimuli stereograms and using prisms for generating the prismatic effects.

In recent years, flat-panel display (FPD) technology has undergone great development, and now FPDs appear in many devices. A significant element in FPD manufacturing is the display front surface. Manufacturers sell FPDs with different types of front surfaces, which can be matte (also called anti-glare) or glossy screens. Users who prefer glossy screens consider these displays to show more vivid colors compared with matte-screen displays. However, on the glossy screens, external light sources may cause unpleasant reflections that can be reduced by a matte treatment in the front surface. In this work, we present a method to characterize FPD screens using laser-speckle patterns. We characterize three FPDs: a Samsung XL2370 LCD monitor of 23 in. with matte screen, a Toshiba Satellite A100 LCD laptop of 15.4 in. with glossy screen, and a Grammata Papyre 6.1 electronic book reader of 6 in. with ePaper screen (E-ink technology). The results show great differences in speckle-contrast values for the three screens characterized and, therefore, this work shows the feasibility of this method for characterizing and comparing FPDs that have different types of front surfaces.

We present a method for comparing the optical quality of spectacle lenses based on determining the modulation transfer function (MTF) using random-dot patterns. Furthermore, we determine the precision of the method under repeatability conditions of measurement. The experimental device is composed of a laptop computer in which the LCD monitor presents the random-dot pattern, a liquid-crystal tunable filter, the lens under test, and a charge-coupled device detector connected to its control card installed in another computer. The method proposed has major advantages: the lenses can be characterized at different wavelengths; no additional sources to illuminate the pattern are required, the monitor's lighting source itself is used; and the characteristics of the pattern can be quickly and easily modified, as we install the control software in the laptop computer. We analyze three spherical spectacle lenses (+5 D) from different manufacturers and, in terms of MTF, the greatest difference found between them is 13.7%. The uncertainty associated with this method falls within the range of 0.001 and 0.06. Given the low uncertainty values, differences found between the lenses are significant. Therefore, the method proposed is a versatile and quick technique to distinguish the optical quality of spectacle lenses from different manufacturers.

Today, CCD and CMOS detector arrays present excellent features in imaging systems. To investigate the suitability of each technology according to various applications, in this work we have comparatively studied the quality of the images provided by different cameras. To this end we have used the speckle method to determine the modulation transfer function (MTF) at different wavelengths of the visible spectrum for the detectors of a low-cost CCD video camera and of two scientific cameras (CCD and CMOS). For both the low-cost CCD and the scientific CMOS detectors, the differences between the MTF curves intensify as the spatial frequency augments, while the MTF decreases as the wavelength increases. For the scientific CCD detector, the MTF spectral behavior does not show this trend, and the differences between the MTF curves corresponding to extreme wavelengths are not expected to be significant, as opposed to what appears for the scientific CMOS detector.

From the luminance distribution measured with a stereoluminancemeter we have studied the variation in the principal indices of discomfort glare while considering the orientation of the line of vision of the observer and the limiting luminance of the glare source. This method provides the ideal orientation for the observer in a lighted environment, minimizes the detrimental effects of glare, and determines the reliability of the indices calculated for discomfort glare.