ψ¯(𝐗,t)=∫C(𝐗,t,λ)ac(λ)dλ\overline{\psi} (\mathbf{X},t) = \int C(\mathbf{X},t,\lambda)a_c(\lambda)d\lambda 𝐗\mathbf{X}: 3D position in a world coordinate, 𝑎c(λ)𝑎_c (λ) :the camera sensor frequency response