Super Vision: Spectral-based Tetrachromatic Model - How Leiothrix lutea See the UV World?

Abstract

　Tracing the evolution of mammals，our common ancestor, vertebrates were originally tetrachromat, but retreated to nocturnal dichromat in the Mesozoic dinosaurs age. The primates regained the diurnal after the extinction of dinosaurs. About 35 million years ago, human beings won the LMS trichromacy by mutations in the gene duplication process.　Birds are typical tetrachromat with the fourth UV cone and a valuable taxon that inherits the color vision of our common ancestors now. It's interesting if possible to glimpse the UV world from the color vision of birds that our anchesters were seing.

　In this paper, we extend the Matrix-R theory to tetrachromacy and try to estimate "how Leiothrix lutea sees the UV world with ROGU cone sensors? ". The extended matrix R₄, which is created from the basis functions of ROGU, projects an input spectrum C(λ)onto FCS(Fundamental Color Space)of Leiothrix lutea. The matrix R₄ extracts the spectrum C^*₄(λ)called "fundamental " from C(λ),that is, visible to Leiothrix lutea. First, tetra-chromatic ROGU stimulus in a scene is estimated from tri-chromatic sRGB camera image by a simple linear model. Next, the fundamental C ^*₄(λ)is restored by the pseudo-inverse projection of ROGU stimulus. Finally, C^*₄(λ)is separated to four-color channels of(Red, Orange, Green, and UV)and the UV channel is visualized by colorization. A true fundamental C ^*₄(λ)is calculated by operating the matrix R₄ onto a measured real spectrum C(λ)and is examined how it matches with the estimated C _^*4(λ).