Figure 4. Pecopteris spp. Coal Measures, Upper Carboniferous, Forest of Dean, England.  4.1. One virtual light source normal to surface. 4.2. Oblique virtual light source from NE, comparable with traditional photograph. 4.3. Diffuse gain, providing subtle improvement in some regions but not in others. 4.4. Specular enhancement. Note "whitening" effect.

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