In reality, the light is composed of waves with different wavelengths. The waves visible to human eye make up the spectrum. The daylight spectrum ranges from 380nm to 780nm, starting from violet, through blue, green, yellow to red, faded to black at both ends. When a spot appears white, it means that all wavelengths reach the eye. When we see yellow, all but the blue (complementary) rays hit the retina, for green it is all waves except for the purple rays and so on. Waves in the spectrum have various properties, i.e. speed which can be observed through phenomena such as dispersion or diffraction.




The Spectrum plugin-set has been developed to provide an effective way of visualizing a variety of spectral phenomena. In other words, the Spectrum's engine offers a physically correct simulations, includes all kinds of non-photo real features for artists, and has been optimized to stretch to any type of production.


Key Benefits

Spectrum accounts for photorealism. It's a must for all transparent-surface visualizations, like glass, liquids, crystals, anisotropic materials, diffraction gratings, and natural phenomena such as rainbows. Besides, it offers an excellent basis for credible fictions and stylized photo-realism.

Spectrum accounts for photorealism. It's a must for all transparent-surface visualizations, like glass, liquids, crystals, anisotropic materials, diffraction gratings, and natural phenomena such as rainbows. Besides, it offers an excellent basis for credible fictions and stylized photo-realism.

From the visual point of view, Spectrum has a strong impact on composition. By its colorful fringes, it emphasizes intensive spots in the lighting scheme, and generally adds to the color variation.

For all abstract-art fans, Spectrum alone can turn even the most simple scenes into something visually impressive.


Implementation

The Spectrum set consists of 3 independent LW plugins, each optimized for a particular spectral simulation: Dispersion Shader, Diffraction Shader, LensFlares Pixelfilter. Both shaders are based on LW's raytracing. The LensFlares pixelfilter works as pure planar effect. All parameters in each handler can be enveloped and texturized. The flexibility of the overall system is greatly enhanced by a number of custom gradient inputs.


Dispersion

By definition, when a light ray enters a new optical medium, it refracts according to the indices of refraction of mediums on both sides of the optical interface. In 3D, dispersion is an advanced approach to refraction simulation, where each wavelength has a different index of refraction and thus refracts under different angle. Briefly, the Dispersion Shader simulates accurate refractions automatically with no 'air polygons' necessary. It handles multiple bounces efficiently, offers artistic uniform dispersion, supports absorption, and is fully multithreading-optimized.





Spectrum features correct single-layer refractions, which is the reason why it should be applied to plain refraction simulation, as well. The problem with proper ray-bouncing when exiting an optical medium was solved by a double IOR value, assigned per surface, and defining each side of the optical interface. The first picture presents the common refraction error by LW, the second shows the correct refractions by the Dispersion Shader (no spectral effect here).





When assigned to a surface that is placed in front of the camera, Dispersion can serve as a "spectral raytracer", i.e. simulating chromatic aberration of the camera lens. The actual dispersion spread is defined through a gradient texture assigning a custom IOR value to each wavelength.


Diffraction

In optics, diffraction occurs when a beam of light encounters a slit the size that is comparable to the wavelength of the spectrum (380nm - 780nm). Every spot on the slit acts as a secondary light source that interferes with the original beam. The Diffraction Shader is optimized for single-direction grooves defined by a tangent-space vector. Diffracted rays are spread around the slit vector, which from an artistic point of view, makes the reflection / transparency blurred in the direction perpendicular to the slit vector. Reflective (upper row) and transparent (lower row) diffraction gratings both are supported. Since the users can apply several instances of the shader, surfaces with multi-directional grooves can be visualized as well.






Lens Flares

The blades of a camera's aperture also make up a system of slits that diffracts light. Both dispersion and diffraction apply to all light rays, however, as their intensity gets divided, spectral phenomena from only the intensive spots are visible. That's just what happens when a strong light source is being photographed - instead of a single pixel, complex diffraction pattern arises.






The LensFlares pixelfilter, the third part of the Spectrum plugin set, renders aperture diffraction diagrams. Just like with real cameras, the lens flares are pure planar, spot-based phenomenon, hence the bounced light and all other intensive spots will account for the effect.


Limitations

The color of Spectrum's shaders is not considered by LW caustics, in fact no shader's color is considered by LW caustics. For the time being, dispersive caustics can be effectively faked by the application of custom reflections of HyperSmooth, or as a colored shadow of Shadow Designer.


Requirements

Lightwave 7.0 or higher
WinNT, Win2000, OS 9, OS X
At least 128mb ram recommended