Welcome to Morpho Butterfly Rendering
The male of a species of Morpho butterfly native to Central and South America, is known as the "jewel of the Amazon," and displays a mysterious brilliant iridescent blue color, without any pigmentation. One of the most interesting features of the Morpho butterfly is backscattering — light is not specularly reflected but instead reflects backwards to the source. The Morpho blue and backscattering is due to optical interference in photonic crystal-like nano-structures on its scales, which selectively reflect blue. Color without pigments is called "structural color." Structural colors are difficult to render even with advanced rendering methods, because most of these methods are based on geometric optics, such as the ray tracing, which is invalid for nano-structures. A rigorous nano-optical treatment is required to correctly render the color.  Fig. 1. Pipeline to render the structural color of a male Morpho butterfly: (a) Transmission electron microscope image of a butterfly scale. Numerous photonic crystal-like ridges are visible. (b) Model of a single ridge. Diffraction spots due to a periodic structure can be canceled out by the averaging effect of ridges with random heights on the butterfly scales. (c) Simulated nano-optics based bidirectional reflectance distribution function (BRDF) (θ = incidence angle, φ = reflection angle). The BRDF is obtained using the near-to-far field transformation and the color system transformation. (d) Rendered image of a male Morpho butterfly. We introduce a rendering method based on high accuracy nano-optical simulations using the nonstandard finite-difference time-domain (FDTD) algorithm. The rendering procedure is shown in Fig. 1. The rendering pipeline can be summarized as follows: (1) Model nano-structures from a transmission electron microscope image; (2) Simulate light scattering from the butterfly scale model using the NS-FDTD algorithm; (3) Using the near-to-far field transformation and the color system transformation, obtain a nano-optics based bidirectional reflectance distribution function (BRDF); (4) Render the butterfly image using the BRDF. We explain this work in 4 sections:
By comparing with optical measurements of Morpho butterfly scales, we validated the simulation result and its rendering. Our CG animation of Morpho rhetenor butterflies can be seen at Youtube as below. PublicationThis work has been published as
Copyright (C) 2011 Naoki Okada, All Rights Reserved.
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