\( I(x,y)=\int_0^D \) \(C\)\((\)\(s\)\((\)\(\mathbf{x}(\lambda)\)\()))\)\(\tau\)\((\)\(s\)\((\)\(\mathbf{x}(\lambda)\)\())) \times \exp\left(-\int_0^\lambda\tau(s(\mathbf{x}(\lambda'))) \mathrm{d}\lambda'\right)\mathrm{d}\lambda\),

where \( D \) is the ray length, \( C(s(x(\lambda))) \) is the reflected/emitted light, \( \tau (s(x(\lambda))) \) is the light extinction coefficient, \( s(x(\lambda)) \) is the scalar value at position \( x \) in the ray parameterized by \( \lambda\).