The effects of habitat structure and lighting on object and background appearance

Abstract The color, geometry, and lighting of environments characterize their appearance to humans and other animals and, as a result, play an important role in the evolution of animal coloration. Yet despite this long-standing association, how changes in lighting from atmospheric conditions and three-dimensional geometry interact to alter the appearance of scenes and animals remains largely unexplored. To investigate these interactions, we quantified the appearance of natural backgrounds and standardized targets with color-calibrated photographs and 3-dimensional (3D) scans of 672 natural scenes taken under diffuse and direct lighting conditions. We find several instances where lighting and the local 3D environment systematically altered the colors and patterns of scenes and a target object, as well as their relationship with spatial scale. Shadows formed under direct lighting increased luminance and short-long wave (blue-yellow) contrast across spatial scales, especially at larger spatial scales for habitats with a greater 3D variation. Conversely, medium-long wave (green-red) information was highly stable to changes in lighting. Direct lighting and the 3D environment also influenced the directionality and orientation of patterns within the scenes and targets due to the formation of cast and self-shadows of different orientations. These analyses demonstrate the importance of considering the lighting and geometry of an environment when comparing the statistics of animals and their backgrounds. Competing Interest Statement The authors have declared no competing interest. Glossary - Term - Definition - Anisotropy - The heterogeneity of orientation; can be applied to either a pattern (e.g., stripes are highly anisotropic/directional, but spots are isotropic/directionless) or an illuminant (directional or diffuse). - Cast shadows - Cast shadows: shadows projected onto ambient surfaces/objects. - Chromatic contrast - Contrast in hue as opposed to overall intensity. - Dappled lighting - Patches of shadow created by multiple objects between the illuminant and the target. - Diffuse lighting - Lighting in which the light on the working plane or on an object is not incident predominantly from a particular direction (CIE 1957), e.g., under cloudy conditions or in a photography tent. - Direct lighting - Light, which is highly directional in its intensity, capable of casting well-defined shadows, e.g., on a clear sunny day or from a single artificial light source. - Habitat Geometry - The three-dimensional structure of a habitat. - Maculation - Markings on top of a base color, e.g., leopard rosettes or speckled eggs. - Received shadow - Shadows cast onto the target/subject-object by ambient surfaces/objects. - Self-shadow - Shadows cast onto a target/object by its own geometry, e.g., shaded underbelly. - Soft Shadows - Low-contrast shadows created under diffuse lighting or when the shadowing object is distal to the surface, for example within forested environments. - Depth variation - The level of fluctuation in surface depth. Coarse surfaces are highly variable while smooth surfaces are less variable. - Target - An object of interest for an observer, for example, a prey animal. - Visual scene - The field of visual information observed at a given place and time.