Using digital cameras to investigate animal colouration: estimating sensor sensitivity functions |
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Authors: | Thomas W Pike |
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Institution: | (1) Centre for Ecology and Conservation, School of Biosciences, University of Exeter (Cornwall Campus), Penryn, TR10 9EZ, UK |
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Abstract: | Spectrophotometers allow the objective measurement of colour and as a result are rapidly becoming a key piece of equipment
in the study of animal colouration; however, they also have some major limitations. For example, they can only record point
samples, making it difficult to reconstruct topographical information, and they generally require subjects to be inanimate
during measurement. Recently, the use of digital cameras has been explored as an alternative to spectrophotometry. In particular,
this allows whole scenes to be captured and objectively converted to animal colour space, providing spatial (and potentially
temporal) data that would be unobtainable using spectrophotometry; however, mapping between camera and animal colour spaces
requires knowledge of the spectral sensitivity functions of the camera’s sensors. This information is rarely available, and
making direct measures of sensor sensitivity can be prohibitively expensive, technically demanding and time-consuming. As
a result, various methods have been developed in the engineering and computing sciences that allow sensor sensitivity functions
to be estimated using only readily collected data on the camera’s response to a limited number of colour patches of known
surface reflectance. Here, I describe the practical application of one such method and demonstrate how it allows the recovery
of sensor sensitivities (including in the ultraviolet) with a high enough degree of accuracy to reconstruct whole images in
terms of the quantal catches of an animal’s photoreceptors, with calculated values that closely match those determined from
spectrophotometric measurements. I discuss the potential for this method to advance our understanding of animal colouration. |
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