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Hyperspectral optical imaging of two different species of lepidoptera.

Medina JM, Nascimento SM, Vukusic P - Nanoscale Res Lett (2011)

Bottom Line: Color coordinates from reflectance spectra were calculated taking into account human spectral sensitivity.For each butterfly wing, the observed color is described by a characteristic color map in the chromaticity diagram and spreads over a limited volume in the color space.The results suggest that variability in the reflectance spectra is correlated with different random arrangements in the spatial distribution of the scales that cover the wing membranes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre of Physics, University of Minho, Campus de Gualtar, Braga, 4710-057, Portugal. jmanuel@fisica.uminho.pt.

ABSTRACT
In this article, we report a hyperspectral optical imaging application for measurement of the reflectance spectra of photonic structures that produce structural colors with high spatial resolution. The measurement of the spectral reflectance function is exemplified in the butterfly wings of two different species of Lepidoptera: the blue iridescence reflected by the nymphalid Morpho didius and the green iridescence of the papilionid Papilio palinurus. Color coordinates from reflectance spectra were calculated taking into account human spectral sensitivity. For each butterfly wing, the observed color is described by a characteristic color map in the chromaticity diagram and spreads over a limited volume in the color space. The results suggest that variability in the reflectance spectra is correlated with different random arrangements in the spatial distribution of the scales that cover the wing membranes. Hyperspectral optical imaging opens new ways for the non-invasive study and classification of different forms of irregularity in structural colors.

No MeSH data available.


Related in: MedlinePlus

The entire selected imaging areas in the sRGB color space (size 400 × 400 pixels). (a) M. didius and (b) P. palinurus. At each pixel, color coordinates were generated from reflectance spectra as the CIE XYZ tristimulus values and then converted to the sRGB color space.
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Figure 3: The entire selected imaging areas in the sRGB color space (size 400 × 400 pixels). (a) M. didius and (b) P. palinurus. At each pixel, color coordinates were generated from reflectance spectra as the CIE XYZ tristimulus values and then converted to the sRGB color space.

Mentions: Figure 3a, b represents the selected area for hyperspectral imaging for M. didius and P. palinurus, respectively. The studied part of each butterfly wing covers a surface of 400 × 400 pixels at the center of the hyperspectral cube giving 1.6 × 105 reflectances. At each pixel position, the CIE XYZ tristimulus values were calculated from reflectance spectra and then converted to the sRGB color space. In both cases, the wing veins can be observed as dark-lined features. Color appearance qualitatively agrees with direct visual inspection of the samples. Figure 4a represents the chromaticity coordinates in the CIE-1931 chromaticity diagram. Figure 4b shows the three-dimensional representation in the CIELAB color space (the illuminant D65 was used). The CIELAB space is intended for the representation of pigmented coatings [2]. Alternatively, Figure 4c shows the a*b* plane in polar coordinates, with the chroma C* as the radial coordinate (related with saturation or the reciprocal of white), and the hue-angle hab as the polar angle [2]. The results in Figure 2 indicate that variability in the reflectance spectra is mainly due to the intrinsic disorder in the structure of the butterfly wings. Figures 3 and 4 also show that irregularity is mapped in an extended color gamut. The color gamut in the M. didius is different from the P. palinurus. These color maps suggest a possible dependency with specific random arrangements of the scales and ridges such as the relative tilt angle distribution in the wing membranes [1,7]. The combination of hyperspectral imaging and accurate reflectance modeling may be important for improved understanding of the intrinsic disorder in butterfly wings and in industrial tunable structural colors.


Hyperspectral optical imaging of two different species of lepidoptera.

Medina JM, Nascimento SM, Vukusic P - Nanoscale Res Lett (2011)

The entire selected imaging areas in the sRGB color space (size 400 × 400 pixels). (a) M. didius and (b) P. palinurus. At each pixel, color coordinates were generated from reflectance spectra as the CIE XYZ tristimulus values and then converted to the sRGB color space.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211459&req=5

Figure 3: The entire selected imaging areas in the sRGB color space (size 400 × 400 pixels). (a) M. didius and (b) P. palinurus. At each pixel, color coordinates were generated from reflectance spectra as the CIE XYZ tristimulus values and then converted to the sRGB color space.
Mentions: Figure 3a, b represents the selected area for hyperspectral imaging for M. didius and P. palinurus, respectively. The studied part of each butterfly wing covers a surface of 400 × 400 pixels at the center of the hyperspectral cube giving 1.6 × 105 reflectances. At each pixel position, the CIE XYZ tristimulus values were calculated from reflectance spectra and then converted to the sRGB color space. In both cases, the wing veins can be observed as dark-lined features. Color appearance qualitatively agrees with direct visual inspection of the samples. Figure 4a represents the chromaticity coordinates in the CIE-1931 chromaticity diagram. Figure 4b shows the three-dimensional representation in the CIELAB color space (the illuminant D65 was used). The CIELAB space is intended for the representation of pigmented coatings [2]. Alternatively, Figure 4c shows the a*b* plane in polar coordinates, with the chroma C* as the radial coordinate (related with saturation or the reciprocal of white), and the hue-angle hab as the polar angle [2]. The results in Figure 2 indicate that variability in the reflectance spectra is mainly due to the intrinsic disorder in the structure of the butterfly wings. Figures 3 and 4 also show that irregularity is mapped in an extended color gamut. The color gamut in the M. didius is different from the P. palinurus. These color maps suggest a possible dependency with specific random arrangements of the scales and ridges such as the relative tilt angle distribution in the wing membranes [1,7]. The combination of hyperspectral imaging and accurate reflectance modeling may be important for improved understanding of the intrinsic disorder in butterfly wings and in industrial tunable structural colors.

Bottom Line: Color coordinates from reflectance spectra were calculated taking into account human spectral sensitivity.For each butterfly wing, the observed color is described by a characteristic color map in the chromaticity diagram and spreads over a limited volume in the color space.The results suggest that variability in the reflectance spectra is correlated with different random arrangements in the spatial distribution of the scales that cover the wing membranes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre of Physics, University of Minho, Campus de Gualtar, Braga, 4710-057, Portugal. jmanuel@fisica.uminho.pt.

ABSTRACT
In this article, we report a hyperspectral optical imaging application for measurement of the reflectance spectra of photonic structures that produce structural colors with high spatial resolution. The measurement of the spectral reflectance function is exemplified in the butterfly wings of two different species of Lepidoptera: the blue iridescence reflected by the nymphalid Morpho didius and the green iridescence of the papilionid Papilio palinurus. Color coordinates from reflectance spectra were calculated taking into account human spectral sensitivity. For each butterfly wing, the observed color is described by a characteristic color map in the chromaticity diagram and spreads over a limited volume in the color space. The results suggest that variability in the reflectance spectra is correlated with different random arrangements in the spatial distribution of the scales that cover the wing membranes. Hyperspectral optical imaging opens new ways for the non-invasive study and classification of different forms of irregularity in structural colors.

No MeSH data available.


Related in: MedlinePlus