Metrics and statistics of frequency of occurrence of metamerism in consumer cameras for natural scenes.

This paper presents metrics and statistics of frequency of occurrence of metamerism in three consumer cameras, viz., Canon 1D Mark III, Nikon D40, and Sony α7, using spectral and RGB images of natural scenes. Both sensor metamerism and observer metamerism of the cameras' sensors are studied. We use the concept of dissimilarity of two spectral power distributions in the spectral domain and the RGB domain for studying the occurrence sensor metamerism. Specifically, we use angular difference and digital equivalence approaches for this purpose. For studying the occurrence observer metamerism, we use the weighted Nimeroff's index for dissimilarity in the spectral domain with respect to the CIE color space along with the conventionally used CIE LAB color difference for dissimilarity in the CIE color space. The statistics of the frequency of occurrence of metamerism are generated on a dataset of 423 spectral images of indoor scenes in 5 illumination conditions and outdoor scenes in natural illumination conditions. Experiments show that about 18%-22% of the pixels in the images are metameric in the sense of angular difference. It is also observed that 1%-4% of the colors that would have appeared similar to human eyes are reproduced as distinct colors in the cameras. Dataset and details can be found at https://sites.google.com/site/dilipprasad/source-codes.