Enrique Hita

Note. Visual and Instrumental Color Evaluation in Red Wines

The color of 15 red wines from several wineries within the renowned wine-producing region Rioja (Northern Spain) was measured by spectrophotometric and spectroradiometric techniques and was visually assessed in a pair-comparison experiment by a panel of 10 experienced observers having normal color vision. Correlation between instrumental color measurements made by spectrophotometric and spectroradiometric techniques was very low, as expected from major differences in the experimental conditions employed (different illumination, path lengths and glass effects). Spectroradiometric measurements at the center of the wine sampler and at positions displaced 1 cm in the horizontal and vertical directions were quite different, mainly because of an increase of the lightness L*, the average color differences between them being high (3.5 and 2.6 CIELAB units, respectively). A 50% acceptance percentage resulted for a color difference of 2.8 CIELAB units, using a reference anchor-pair of wine samples with 4.0 CIELAB units. Thus, a value around 3.0 CIELAB units should be considered a preliminary estimate of the acceptable tolerance by the human eye for red wines poured in standard wine samplers.

Changes in corneal asphericity after laser in situ keratomileusis

Purpose: To analyze the origin of the changes in corneal asphericity (p‐factor) after laser in situ keratomileusis (LASIK) and the effect of postsurgery asphericity on contrast‐sensitivity function (CSF) under photopic conditions. Setting: Department of Optics, University of Granada, Granada, Spain. Methods: The p‐factor and CSF (best corrected before surgery and 1, 3, and 6 months after surgery) were measured in 24 eyes. Results: An increase in the p‐factor after LASIK was noted; there was an 87.2% change in the asphericity using the paraxial formula of Munnerlyn and coauthors. Other factors such as decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures, and reflection losses of the laser on the cornea could account for the greater than expected increase (12.8%) in the p‐factor. The CSF measurements deteriorated after LASIK; the change was significant (P<.05) in patients with myopia worse than −4.0 diopters at frequencies of 9.2, 12, 15, and 20 cycles per degree. Conclusion: The increase in corneal asphericity after surgery, greater with a higher degree of myopia, and the deterioration in CSF with high myopia justify new ablation algorithms and further study of the variables that could modify the ablation unpredictably.

Changes in corneal asphericity after laser refractive surgery, including reflection losses and nonnormal incidence upon the anterior cornea.

We tested the effects on laser ablation of reflection losses and nonnormal incidence on the anterior cornea. We measured presurgical and postsurgical corneal asphericity in 94 myopic eyes, comparing it with the corneal asphericity predicted by the Munnerlyn formula, modified or not, with an adjustment factor that takes into account the two effects mentioned above. The predictive power of the experimental results was stronger when we considered the adjustment factor. We propose to modify ablation algorithms by taking this adjustment factor into account, especially in customized corneal ablation, which needs high accuracy for correcting eye aberrations.

Variations in corneal sensitivity with hydrogel contact lenses

Abstract. Changes in corneal sensitivity were studied in two groups of healthy subjects who wore hydrogel contact lenses: 44 persons whose lenses contained 38% water, and 23 who wore lenses of 55% water content. Corneal sensitivity decreased in both groups during the first 8 h following insertion; the decrease was more marked in the group who wore 38% water lenses. Changes in corneal tactile sensitivity were greater in women than in men, and determinations in different corneal zones showed that the central zone was less affected in sensitivity than any of the peripheral zones. After lenses were removed, tactile sensitivity showed full recovery within 4 h.

Interocular Differences in Higher-order Aberrations on Binocular Visual Performance

Purpose. To analyze the influence of higher-order aberrations on binocular visual performance under mesopic conditions. Methods. We measured aberrations in both eyes of 35 emmetropic observers with a Wasca aberrometer. Binocular visual performance was checked with both binocular summation for contrast sensitivity function and a parameter that characterizes stereopsis (maximum disparity). Results. Binocular summation and maximum disparity significantly decrease with increasing interocular differences in higher-order aberrations (total, coma, and spherical aberration). Conclusions. At least some aspects of binocular visual performance are less effective for large interocular differences in higher-order eye aberrations.

Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams.

We provide a correction factor to be added in ablation algorithms when a Gaussian beam is used in photorefractive laser surgery. This factor, which quantifies the effect of pulse overlapping, depends on beam radius and spot size. We also deduce the expected post-surgical corneal radius and asphericity when considering this factor. Data on 141 eyes operated on LASIK (laser in situ keratomileusis) with a Gaussian profile show that the discrepancy between experimental and expected data on corneal power is significantly lower when using the correction factor. For an effective improvement of post-surgical visual quality, this factor should be applied in ablation algorithms that do not consider the effects of pulse overlapping with a Gaussian beam.

Temporal aspects of color discrimination

Experimental results obtained for different observers and stimuli are analyzed to study the influence of the exposure time of the test on the differential thresholds of color. Exposure times from 0.2 to 9 sec are studied. A minimum for the differential thresholds of luminance and chromaticity and for the global differential threshold is found around 1 sec.

Optimizing the constant-channel chromaticity and color gamut of CRT color displays by control of brightness and contrast levels

Before a CRT color display is calibrated, the levels of the brightness and contrast controls should be considered. These levels have different effects on the relationship between the chromaticity coordinates of the red-green-blue (RGB) channels and the voltage applied to the gun as well as on the color gamut. Using three different CRT color displays, we measured both these relationships as well as the color gamut for different combinations of brightness and contrast levels. With respect to the luminance range of the white point provided by each display, the results show that the assumption of constant-channel chromaticity of the RGB channels is more valid at medium- to low-brightness levels in combination with high-contrast levels. In addition, this assumption holds at high contrast and medium- to low-brightness levels, the color gamut being optimized at these combinations of levels, with regard to the size of the triangle of primaries-the maximum luminance of the display white point.

Some classical color differences calculated with new formulas

An evaluation of chromatic and color-threshold differences was carried out by using the CMC(l:c) and the BFD(l:c) color-difference formulas [ J. Soc. Dyers Colour.100, 128 ( 1984); J. Soc. Dyers Colour.103, 86 ( 1987)] from experimental threshold results obtained with visual colorimeters [ J. Opt. Soc. Am.32, 247 ( 1942); J. Opt. Soc. Am.39, 808 ( 1949); J. Opt. Soc. Am.47, 137 ( 1957); J. Opt. Soc. Am.61, 1135 ( 1971)]. The good results previously reported on the use of these two new formulas with surface colors are also found for the chromatic differences calculated, especially with the BFD(1:1) formula. In the case of color differences BFD(0.6:1) improves the results achieved with BFD(1:1) and gives results similar to those of CMC(1:1). The claim of CMC(l:c) and BFD(l:c) as sometimes superior alternatives to the currently recommended CIE formulas CIELUV and CIELAB can be supported by the present results.

Optimization of color reproduction on CRT‐color monitors

In the present experimental study, we quantify the influence of the brightness and contrast levels of a CRT- color monitor in the color reproduction of 60 Munsell chips distributed throughout the chromatic diagram. The images were captured by two CCD cameras, and the color differ- ences were evaluated after reproducing the chips on a color monitor (the experiment was performed with 3 different monitors) for 9 combinations of brightness-contrast levels. We evaluated the color differences with 3 different formu- las: CIELAB, CIELUV, and CIE94. The results indicate that the optimal settings of a monitor, to minimize the color differences, is a medium or minimum brightness level in combination with a maximum contrast level. This combina- tion ensures a more faithful color reproduction with respect to the original image.© 1999 John Wiley & Sons, Inc. Col Res Appl,