Spectrums and Spectral Images
Spectrums and Spectral Images
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Spectral aspect of the light
Spectral aspect of the light
Light is a wave traveling in space. Its wavelength is the length of each oscillation (Figure A).
The wavelength defines the color that is perceived : a wave with a wavelength of 400nm will be perceived as blue and a wave with a wavelength of 700nm will be perceived as red (Figure B).
Some wavelengths cannot be perceived by the human eye (infrared above 830 nm, uv and x-rays below 360 nm).
figure A
figure B
https://www.chem.fsu.edu/chemlab/chm1045/estructure.html
Most light sources do not emit light at a single wavelength but they emit a combination of multiple wavelengths with different intensities. All of these wavelengths make up the light spectrum.
intensity as a function of wavelength, example of a spectrum perceived as blue
The way we perceive the appearance of materials also depends on their spectral characteristics : the material reflects, diffracts and absorbs the light depending on its wavelength. Some examples of situations where the spectral characteristics of a material has an influence on its appearance could be :
two materials that can be perceived as similar under a light source and different under another (example 1)
very thin layers of reflective/transmissive material (soap bubbles, very thin coatings,...) that can create interference (example 2)
materials with refractive index that depends on the wavelength (glass, diamond,...) that can induce dispersion (example 3)
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Example 1 : metameric materials under a D65 illuminant (left) and a F10 illuminant (right)
Example 2 : interference in soap bubbles
Example 3 : dispersion in a diamond or in prisms
Spectrums in the Predict Suite
Spectrums in the Predict Suite
In the Predict Suite, spectrums are required to define materials, lights, and sensors. At the moment, the Alpha plugin only supports the following :
Spectral materials : measured materials of type AxF can contain spectral data. When it is the case, we use it entirely for the simulation,
Spectral lights : materials can have an emissive property which can be defined using a spectrum. See the Lights section for more details,
Sensors spectral response curves : the spectral response of sensors is defined using spectrums. See the Optical Instrument section for more details.
Spectral Images in the Predict Suite
Spectral Images in the Predict Suite
Spectral Images are not currently supported in the Alpha plugin for Unreal, this means HDRIs cannot be spectral. This will be implemented in future plugins.
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