𝐗→P𝐱\mathbf{X} \xrightarrow[P]{} \mathbf{x}
𝐱\mathbf{x}: 2D position in camera plane

Image function:

ψ(P(𝐗),t)=ψ(𝐗,t)\psi(P(\mathbf{X}),t)=\overline{\psi}(\mathbf{X},t)

or

ψ(𝐱,t)=ψ(P−1(𝐱),t)\psi(\mathbf{x},t)=\overline{\psi}(P^{-1}(\mathbf{x}),t)

The projection operator is non-linear
– Perspective projection
– Orthographic projection
– More on this later

ψ(𝐗,t)\overline{\psi} (\mathbf{X},t) is Camera absorption function