Age-related changes of color visual acuity in normal eyes

Purpose To evaluate the age-related change in color visual acuity (CVA) in normal eyes. Methods In total, 162 normal eyes (162 subjects, women: 52, men: 110, age range: 15–68 years) with best-corrected visual acuity (BCVA) ≥20/13 were enrolled. Fifteen colors from the New Color Test (chroma 6) were applied to Landolt “C” rings, white point D65 was applied as background, and a luminance of 30 cd/m2 was set for both the rings and the background. These rings were used to measure the chromatic spatial discrimination acuity as the CVA value, while changing the stimulus size. Correlations of the CVA value of each color and age were evaluated. Mean CVA values of all 15 colors (logarithm of the minimum angle of resolution) were compared between age groups in 10-year increments. Results Nine CVA values (red, yellow-red, red-yellow, green, blue-green, green-blue, purple, red-purple, and purple-red) were negatively correlated with age (all p<0.05); the remaining six (yellow, green-yellow, yellow-green, blue, purple-blue, and blue-purple), as well as BCVA were not. The age groups with the best to worst mean CVA values of 15 colors were as follows: 20–29 (mean ± standard deviation, 0.303 ± 0.113), 30–39 (0.324 ± 0.096), 10–19 (0.333 ± 0.022), 50–59 (0.335 ± 0.078), 40–49 (0.339 ± 0.096), and 60–69 (0.379 ± 0.125) years. There were statistically significant differences between mean CVA values of the following groups: 20–29 and 40–49 years; 20–29 and 60–69 years; 30–39 and 60–69 years (all p<0.01). Conclusions The CVA values related to the medium/long-wavelength-sensitive cones were more susceptible to aging than those related to the short-wavelength-sensitive cones. This differed from previous reports, and may be related to the difference in the range of foveal cone function evaluated with each examination.

The impact of the Helmholtz-Kohlrausch effect on the appearance of near-white paper colours

This paper investigates the impact of the Helmholtz-Kohlrausch effect on near-white substrate colours. As the luminance of the test colour (or its simulated reflectance in a softproof setup) approaches that of the adapting white point the viewing mode changes from 'surface mode' to 'aperture mode', and the appearance of the test colour becomes self-luminous. However, some substrates with optical brighteners fall close to this threshold between viewing modes, since the OBAs not only increase the perceived reflectance but also increase the H-K effect, where it is very prominent in bluish colours. For graphic arts content shown on a display system, this essentially breaks the soft-proofing paradigm. The practical application of this work relates to cross-media colour reproduction, where the lightness appearance of some substrates is not adequately described by their colorimetric values, and this may impact on choice of proofing strategies.

Observer metamerism to display white point between LCD and OLED displays

Displays with different primary sets were found to introduce perceived color mismatch between pairs that are computationally metameric and to affect the degree of observer metamerism. OLED display is becoming more and more popular than LCD display in different imaging systems. In this study, human observers used an LCD and eight OLED displays to match the color appearance of a D 70 white stimulus produced by a spectrally tunable LED device. It was found the chromaticities of the LCD display were significantly different from those of the OLED displays to achieve a match. When the colors were adjusted to have matched appearance, the chromaticities of the OLED displays were always shifted towards closer to the blackbody locus using the CIE 1931 Color Matching Functions (CMFs). The results also suggested that the CIE 2006 2° Color Matching Functions had the best performance.

Observer metamerism: Why do [mis]matches of neutral appear pinkish or greenish?

White lighting and neutral-appearing objects are essential in numerous color applications. In particular, setting or tuning a reference white point is a key procedure in both camera and display applications. Various studies on observer metamerism pointed out that noticeable color disagreements between observers mainly appear in neutral colors. Thus, it is vital to understand how observer metamers of white (or neutral) appear in different colors by different observers. Most observers who participated in a visual demonstration reported that white observer metamers appear pinkish or greenish but rarely yellowish or bluish. In this paper, this intriguing question, "Why observer metamers of white are usually pinkish or greenish?," is addressed based on simulations. Besides, it is also analyzed that which physiological factors play an essential role in this phenomenon and why it is less likely for humans to perceive yellowish or bluish observer metamers of white.

Chromatic Effect Reproduction of Irlen Colored Filters by a Pulse Width Modulation-Driven Three-Chromatic Light Emitting Diode Device

Visual Stress (VS) is an abnormal visuoperceptual condition caused by an imbalance in light adaptation ability which yields reading deficits. It was first described in 1983 and, since then, has been treated with the usage of colored spectral filters, either as Irlen overlays either as lenses for symptoms relief. However, the limited options of overlays compromise the pursuit for the patient’s optimal filter so that a device that could provide a broader range of colors would improve achievements for both screeners and patients. The present work aims to develop a micro-controlled RGB LED device whose goal is to reproduce Irlen overlays combinations chromaticities through colored light metamers. Such a device can open possibilities for better diagnosing Visual Stress (VS) by providing screeners a much more extensive range of colors than regular overlays and glasses and, therefore, allowing more accurate scrutiny of the optimal chromatic point for the patient. For the pursuit of this goal, a LED controller based on PWM (Pulse Width Modulation) of currents was built, and a color reproduction methodology was developed to ensure chromaticity matching. From the 47 filters considered, 22 showed a ratio ΔE/JND < 6 and, thus, laid within a range that could provide the reading performance associated with its corresponding filter. Reproduction methodology was effective and demanded 5 main inputs: LED individual and white point color coordinates plus LED characterization curves. The controller proved to be effective for color manipulation inside the device’s gamut, which opens the possibility for both readjustment of the chromaticity, if it is found to vary with patient’s aging, and further connection to an eye tracker to shorten the search for the optimal point.

The persistent influence of viewing environment illumination color on displayed image appearance

Chromatic adaptation considering competing influences from emissive displays and ambient illumination is a little studied topic in the context of color management in proportion to its influence on displayed image appearance. An experiment was conducted to identify the degree to which observers adapt to the white point of natural images on an emissive display versus the color of ambient illumination in the room. The responses of observers had no significant difference from those of a previous experiment which was conducted with roughly the same procedure and conditions on a mobile display with a significantly smaller viewing angle. A model is proposed to predict the degree of adaptation values reported by observers. This model has a form such that it can be re-optimized to fit additional data sets for different viewing scenarios and can be used in conjunction with a number of chromatic adaptation transforms.

Colorimetry of Luminescent Lanthanide Complexes

Europium, terbium, dysprosium, and samarium are the main trivalent lanthanide ions emitting in the visible spectrum. In this work, the potential of these ions for colorimetric applications and colour reproduction was studied. The conversion of spectral data to colour coordinates was undertaken for three sets of Ln complexes composed of different ligands. We showed that Eu is the most sensitive of the visible Ln ions, regarding ligand-induced colour shifts, due to its hypersensitive transition. Further investigation on the spectral bandwidth of the emission detector, on the wavelengths’ accuracy, on the instrumental correction function, and on the use of incorrect intensity units confirm that the instrumental correction function is the most important spectrophotometric parameter to take into account in order to produce accurate colour values. Finally, we established and discussed the entire colour range (gamut) that can be generated by combining a red-emitting Eu complex with a green-emitting Tb complex and a blue fluorescent compound. The importance of choosing a proper white point is demonstrated. The potential of using different sets of complexes with different spectral fingerprints in order to obtain metameric colours suitable for anti-counterfeiting is also highlighted. This work answers many questions that could arise during a colorimetric analysis of luminescent probes.