Gamut expansion of consumer camera to the CIE XYZ color gamut using a specifically designed fourth sensor channel

This paper discusses the design of an additional spectral filter (i.e., a fourth channel) to be used with existing camera sensors such that the camera's modified color gamut overlaps almost the full CIE XYZ color gamut. The proposed approach leverages on the matrix-R theory that states that the space of metamerism of a sensor, known as the metameric black space, can be determined directly from the camera's spectral sensitivities. Using this metameric black space, a novel fourth channel has been designed on the sensor that can expand the camera's gamut. The effectiveness of this idea has been demonstrated for five commercial cameras, Munsell color chips, and images taken under various illuminations. It is shown that the designed fourth channel is very effective in fitting the camera's color gamuts to CIE XYZ color gamut, reducing CIE LAB colorimetric distances, as well as the color differences between the camera's XYZ images and the true CIE XYZ images.