Local absorption length of photons obtained in the final converged iteration of the standard shock model. The absorption length, given in pc with the color scale, is shown as a function of the photon energy and the distance in the preshock gas (left panel) and in the shock (right panel). Above 911 Å, photons are preferentially absorbed by dust and PAHs. Below this limit, photons are preferentially absorbed by atoms, in particular H, He, and He⁺. The walls seen by the photons below 911 Å correspond to the regions in the preshock and the postshock gas where neutral hydrogren is reformed.