Unique hue correction applied to the color rendering of LED light sources.

Existing color quality indices for light sources provide broad information about different dimensions related to color quality. Color fidelity, harmony, and gamut area are concepts related to these indices, and industry requests this information. For the last few years, LED light sources have been widely used at home and at work, and now a color rendering index that solves the problem of underestimation of this type of light source is needed to provide a score of subjective assessments made by real observers related to color fidelity. In this work, this problem has been studied in two ways, theoretically and experimentally, and the results show discrepancies between the hue composition calculated theoretically using a color appearance model and hue composition evaluated by real observers. These discrepancies could originate from divergences in the color fidelity score and the subjective evaluation of the naturalness of a scene.

Middle Miocene closure of the Central American Seaway.

Uranium-lead geochronology in detrital zircons and provenance analyses in eight boreholes and two surface stratigraphic sections in the northern Andes provide insight into the time of closure of the Central American Seaway. The timing of this closure has been correlated with Plio-Pleistocene global oceanographic, atmospheric, and biotic events. We found that a uniquely Panamanian Eocene detrital zircon fingerprint is pronounced in middle Miocene fluvial and shallow marine strata cropping out in the northern Andes but is absent in underlying lower Miocene and Oligocene strata. We contend that this fingerprint demonstrates a fluvial connection, and therefore the absence of an intervening seaway, between the Panama arc and South America in middle Miocene times; the Central American Seaway had vanished by that time.

Optimization of the correlated color temperature of a light source for a better color discrimination.

In a previous work [J. Opt. Soc. Am. A29, A209 (2012)], we presented a visual color discrimination experiment whose results established the existence of a relationship between the correlated color temperature (CCT) of a light source and the color discrimination capacities of the observers. The results indicated the existence of a statistically significant difference in the color discrimination of unequal sample pairs when using light sources of different color temperatures, with the discrimination capacity being greater the higher the light source's color temperature. That previous work employed an RGBA-LED light source configured with three color temperatures: 2800, 5000, and 6500 K. In order to go a further step in this line, this work expanded the range of color temperatures up to 9700 K. The results showed that there is an optimum CCT of around 5000 K at which observers were found to have a greater color discrimination capability.

Influence of the correlated color temperature of a light source on the color discrimination capacity of the observer.

It is well known that there are different preferences in correlated color temperature of light sources for daily living activities or for viewing artistic paintings. There are also data relating the capacity of observers to make judgments on color differences with the spectral power distribution of the light source used. The present work describes a visual color discrimination experiment whose results confirm the existence of a relationship between the correlated color temperature of a light source and the color discrimination capacities of the observers.

Experimental study of the individual differences in chromatic perception through blue-yellow metameric matches of a white-light continuum.

A metameric colour matching test was designed to study inter-observer variability. Blue-yellow metameric matching to a white-light continuum was used to define the optimal wavelengths at which each of eight non-colour-defective observers achieved a match. The tests involved chromatic stimuli on a 2° bipartite field, with a white-light continuum presented on the left half, and a mixture of two monochromatic stimuli on the right half. The luminance of these chromatic stimuli was adjusted by the researcher using a staircase method, with the observer providing feedback about the similarity in luminance and chromaticity between the two halves of the field. Two series were performed for each observer, using different fixed yellow wavelengths. Since for each fixed yellow wavelength the match with the target white can be achieved by only one corresponding blue wavelength which is particular for each observer, the initial blue wavelengths were approximations based on the 2° CIE 1931 standard observer. Once the observers had attained an achromatic match, they modified the blue wavelength to achieve a perfect match of both halves. Generally, the observers found this modification of the blue wavelength necessary to achieve the metameric match. Each observer had a particular optimal blue wavelength which differed between the two series. The differences between the deviations from the standard observer for the two series were constant in value among the observers.