A multispectral acquisition system to examine the bidirectional reflectance distribution function of structurally colored biological materials in the visible range is presented. We focus on the purple-blue and white-pearl wing scales of the male butterfly Sasakia charonda. Multispectral imaging was done by changing the illumination angular position around the sample as well as that of the specimen around the multispectral sensor axis. Reflectance spectra were transformed to color coordinates and visualized in different color spaces. Spectral analysis shows distinct iridescent patterns in purple-blue and white-pearl scales. Colorimetric analysis indicates that purple-blue scales enhance blue coloring and exhibit higher color saturation. Principal component analysis reveals that the number of principal components that account for more than 99% of reflectance variability was higher in white-pearl scales. This suggests a higher spectral complexity in their spatial color pattern formation. Reconstruction of reflectance spectra from the principal components is discussed. We conclude that multispectral imaging provides new insights into spatial reflectance mapping that result from the combination of structural colorations and variable amounts of absorption pigments.
We have applied principal component analysis to examine trial-to-trial variability of reflectances of automotive coatings that contain effect pigments. Reflectance databases were measured from different color batch productions using a multi-angle spectrophotometer. A method to classify the principal components was used based on the eigenvalue spectra. It was found that the eigenvalue spectra follow distinct power laws and depend on the detection angle. The scaling exponent provided an estimation of the correlation between reflectances and it was higher near specular reflection, suggesting a contribution from the deposition of effect pigments. Our findings indicate that principal component analysis can be a useful tool to classify different sources of spectral variability in color engineering.
We have examined the trial-to-trial variability of the reflectance spectra of surface coatings containing effect pigments. Principal component analysis of reflectances was done at each detection angle separately. A method for classification of principal components is applied based on the eigenvalue spectra. It was found that the eigenvalue spectra follow characteristic power laws and depend on the detection angle. Three different subsets of principal components were examined to separate the relevant spectral features related to the pigments from other noise sources. Reconstruction of the reflectance spectra by taking only the first subset indicated that reflectance variability was higher at near-specular reflection, suggesting a correlation with the trial-to-trial deposition of effect pigments. Reconstruction by using the second subset indicates that variability was higher at short wavelengths. Finally, reconstruction by using only the third subset indicates that reflectance variability was not totally random as a function of the wavelength. The methods employed can be useful in the evaluation of color variability in industrial paint application processes.
KEYWORDS: Color vision, Signal processing, Visualization, Colorimetry, Cones, Visual process modeling, Interference (communication), CRTs, Astatine, Time metrology
We have studied the intrinsic variability of color coding by examining the temporal fluctuations of chromatic-opponent
neurons at the large scale. Simple reaction times were measured for stimuli selected along the red-green direction in the
isoluminant plane of the human color space (S-cone constant or L-M axis). Stimulus size also changed from 8 minutes of
arc to 10 degrees. Fluctuations increased as the mean reaction time increased and showed a bi-linear scaling function.
The coefficient of variation was always lower than predicted by a Poisson process. The variability decreased as a
function of the chromatic contrast and as a function of the stimulus size. The analysis of the hazard functions was
consistent with power-law dominant random processes at low stimulus size and low contrasts and log-normal dominant
processes at high contrasts. Our results conclude that response variability is signal-dependent and evidence for a random
multiplicative process in human color vision. We suggest that multiplicative internal noise modulates red-green spatial
summation and chromatic contrast processing and may represent a fundamental limit in spatially disordered networks.
We report a hyperspectral imaging system to measure the reflectance spectra of real human irises with high spatial resolution. A set of ocular prosthesis was used as the control condition. Reflectance data were decorrelated by the principal-component analysis. The main conclusion is that spectral complexity of the human iris is considerable: between 9 and 11 principal components are necessary to account for 99% of the cumulative variance in human irises. Correcting image misalignments associated with spontaneous ocular movements did not influence this result. The data also suggests a correlation between the first principal component and different levels of melanin present in the irises. It was also found that although the spectral characteristics of the first five principal components were not affected by the radial and angular position of the selected iridal areas, they affect the higher-order ones, suggesting a possible influence of the iris texture. The results show that hyperspectral imaging in the iris, together with adequate spectroscopic analyses provide more information than conventional colorimetric methods, making hyperspectral imaging suitable for the characterization of melanin and the noninvasive diagnosis of ocular diseases and iris color.
Binocular and monocular finger reaction times were measured for circular broad-band stimuli for natural and artificial pupils. Luminance polarity changes were presented at the fovea respect to a reference stimulus under suprathreshold conditions. As in previous studies, binocular reaction times were shorter than monocular with both pupil types. Nevertheless, this binocular summation effect was less marked with the artificial case, becoming more pronounced for dark variations. These result suggest that the near- responses mechanism at the peristriate area of the occipital and at the inferior parietal lobe could support an important role on luminance interactions within the visuomotor pathway.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.