Talk:Photon mapping

It's hard to tell from this article what in particular makes photon mapping a specialisation of ray tracing; I assume it has something to do with the data structure used for "caching" the "photons"... ? Chas zzz brown 07:55 Jan 28, 2003 (UTC)

reverse ray tracing?

The article says that reverse ray tracing originates the light rays at the light source. But doesn't reverse ray tracing have the rays start at the camera? MichaelGensheimer 21:26, 15 Nov 2003 (UTC)

Yes you're correct ColinCren 08:10, 10 February 2007 (UTC)[reply]

Actually, quoting from Foley et al., Computer Graphics: Principles and Practice, p. 792: "It might seem that we would need only to run a conventional ray tracer "backward" from the light sources to the eye to achieve these effects. This concept has been called backward ray tracing, to indicate that it runs in the reverse direction from regular ray tracing, but it is also known as forward ray tracing to stress that it follows the actual path from the lights to the eye. We call it ray tracing from the light sources to avoid confusion!" Sampo Smolander (talk) 20:15, 25 November 2007 (UTC)[reply]

Photon energy

You write "... to decrease the energy of the photon ...". I suppose this does not refer to the engery of a photon in a physical sense. Since the energy of a photon is related to its frequency by E = hf, changing the energy will change its frequency. On the other hand, the frequency distribution of light determines its color. --Borishollas (talk) 17:23, 8 December 2007 (UTC)[reply]

Energy, in the sense of Joules, is not what is literally intended. Rather, a "photon" in photon mapping refers to a collection of light particles, and that when they strike an object, some are reflected and some are absorbed. In this sense, the "energy" (or total particles in the collection) decreases. The Monte Carlo method more accurately describes what is happening with collisions, except it treats the photons as individual light particles instead of as a group of them.

On another note, frequency does NOT necessarily determine color in real life. For example, there is no frequency of a photon for pink, rather the human eye interprets a combination of different frequencies as that color. (Similar to how yellow can be seen from yellow photons as well as from a mixture of red and green ones) Xcelerate (talk) 01:15, 18 January 2008 (UTC)[reply]