Jesús Zoido

The characteristic matrix of a colour detection system

Colour detection systems can be specified in terms of a set of spectral functions (colour-matching functions in the case of human observers). By taking these functions into account we define the characteristic matrix associated with a given colour detection system. This definition provides a new way to evaluate the differences and similarities between the colorimetric behaviour of two colour detection systems. We have applied this formalism to the case of a set of colour-matching functions associated with human observers. The differences between the diagonal terms, , of the characteristic matrices associated with a given couple of observers provides us with information about the differences between their corresponding ith matching functions. The distance between two characteristic matrices, defined in terms of the norm, is a measure of the global difference between the colorimetric behaviour of the corresponding couple of associated observers. It seems to the authors that the characteristic matrix could play an important role in the characterization and design of colour detection and colour reproduction systems.

Improved linear programming method to generate metameric spectral distributions.

We present an application of linear-programming techniques to generate metameric spectral radiant power distributions. Conditions concerning physical color properties, dominant wavelength, and excitation purity lead us to propose criteria that provide distributions associated with color stimuli with high-excitation purity values of any brightness. An unlimited number of metameric distributions can be obtained from the degrees of freedom introduced by the proposed criteria.

Statistics of color-matching experimental data

By assuming that color matches are normally distributed in XYZ space, we present a rigorous statistical technique to obtain regions of equally noticeable chromaticity differences. The probability density function of color matches in (x, y, Y) space is calculated according to standard techniques in probability theory. The geometry of the chromaticity thresholds is computed for various confidence levels alpha. Because of the asymmetry of the probability density function in (x, y, Y) space, the chromaticity thresholds are not symmetrical around the color center. The asymmetries depend on the color center, and they increase when high confidence levels (alpha < 0.32) are considered. It is our opinion that the technique proposed here can provide a useful tool for checking and evaluating deviations from the elliptic geometry of the chromaticity thresholds. It is formally demonstrated that regions of equally noticeable chromaticity differences are not ellipses when the normality hypothesis is assumed in XYZ space.

Colorimetric matching by minimum-square-error fitting

Least-squares approximation can be used in image-based colorimetry once the set of sampling functions is selected. We discuss the accuracy obtained in earlier research, and we compare it with a better calculation method.

Spatial characterization of light detectors with nanometric resolution

The miniaturization of light detectors in the visible and infrared has produced devices with micrometric and sub-micrometric spatial features. Some of these spatial features are closely linked with the physical mechanism of detection. An example of these devices is an optical antennas. To spatially characterize optical antennas it is necessary to scan a probe beam on the plane of the optical antenna. The mapping of this response is then treated and analyzed. When the response of the antenna is monitorized at visible or near-infrared frequencies, a sub-micron scanning step is necessary. In this paper we show the experimental set-up of a measurement station having a spatial resolution of 50 nanometers. This station is devoted to spatially characterize micrometric detectors, and specially optical antennas. The origin of the uncertainties of the measurement protocol is shown and practically analyzed. This station is also applied for characterizing the temporal, spectral, and polarization sensitivity specifications of light detectors with the previously mentioned resolution.

Chromatic perception of non-invasive lighting of cave paintings

This work is intended to deal with the problems which arise when illuminanting Paleolithic cave paintings. We have carried out the spectral and colorimetric characterization of some paintings located in the Murcielagos (bats) cave (Zuheros, Córdoba, Spain). From this characterization, the chromatic changes produced under different lighting conditions are analysed. The damage function is also computed for the different illuminants used. From the results obtained, it is proposed an illuminant whose spectral distribution diminishes the damage by minimizing the absorption of radiation and optimises the color perception of the paintings in this cave. The procedure followed in this study can be applied to optimise the lighting systems used when illuminating any other art work