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I just wonder why author named ray tracing as path tracing..

by leowoo91 7y ago

iamnotacrook 7y ago
They didn't; they're talking about path tracing.
- leowoo91 7y ago
  ok found few answers: https://www.quora.com/Whats-the-difference-between-ray-tracing-and-path-tracing https://www.quora.com/Whats-the-difference-between-ray-traci...
sampo 7y ago
> I just wonder why author named ray tracing as path tracing.. Ray casting (1968) was simply casting rays from camera, one per each image pixel, until the ray hits the closest object. Then the pixel gets the color from the object. Ray tracing (1979) made ray casting recursive for three cases: 1. Reflection: The object surface is a perfect mirror, so we calculate the reflection angle from the incoming ray angle, and continue the process. 2. Refraction: The object is transparent, like glass. The Fresnel equations give the refraction (transmission) and reflection angles and the distribution of energy between them. For some angles, one of these can be 0. 3. Shadow ray: Shadow rays are traced towards each light source. If the shadow ray is blocked by any other object, we're in shadow in respect of that light source. If a light source is visible, both the light source color and the object surface color contribute to the color of this pixel. The object surface can also have a reflectance model (BRDF) so it doesn't need to be a matte Lambertian surface, but the BRDF is only applied to light coming directly from the light sources. An object can have partially reflective surface (like glossy plastic), and it can also be partially transparent (like colored glass). So at each intersection, we may generate up to all 3 types of rays. What we miss here, is that all surfaces diffusely reflect light to some amount, and that the colors in all diffuse incoming light from every direction contributes to the color of a surface, not just direct light from visible light sources. (We also miss caustics. Most notably, a transparent glass ball between the surface and a light source will only give a shadow in ray tracing.) Historically, there was a time when computers were too slow for sampling, even statistically weighted importance sampling, of diffuse light coming from all directions to all surfaces. So the above model of handling only 3 types of rays (mirror reflection, transparent object refraction, light directly from a light source) became both popular, and established as ray tracing. Then later, advances towards including all kinds of physically possible light rays, adopted names other than ray tracing. They are still tracing rays, but they are not called tray tracing, because the name ray tracing is understood to mean only the first method that got widely popular, with all its limitations.
- leowoo91 7y ago
  You almost touched photon mapping there but as long as rays start only from the screen, there is nothing wrong calling anything varying as ray tracing. Limiting reflection count or having multiple rays (monte-carlo) are often aligned with priciples you described.
  - quickthrower2 7y ago
    Photon mapping? As in can render diffraction?
    - magicalhippo 7y ago
      Simplified, photon mapping is a technique where you shoot rays from the light sources and then record the hits on geometry. Name comes from pretending you're tracing a photon bouncing around. Then, when doing the regular ray/path tracing, at each intersection of the camera-ray, you see if the intersection location is near any of the light-ray hits. If so, add in some contribution from the light-ray hits. This avoids you having to explicitly check each light at each intersection point, saving you quite a number of visibility tests. Also, due to the smoothing kernel used when the "photon contributions" are added up, it leads to low-frequency noise rather than high-frequency noise that is normal in regular path tracing. This is especially noticeable when caustics are involved. A nice introduction to the technique can be found here: https://web.cs.wpi.edu/~emmanuel/courses/cs563/write_ups/zackw/photon_mapping/PhotonMapping.html https://web.cs.wpi.edu/~emmanuel/courses/cs563/write_ups/zac...

I just wonder why author named ray tracing as path tracing..

iamnotacrook 7y ago

They didn't; they're talking about path tracing.

leowoo91 7y ago
ok found few answers: https://www.quora.com/Whats-the-difference-between-ray-tracing-and-path-tracing https://www.quora.com/Whats-the-difference-between-ray-traci...

sampo 7y ago

> I just wonder why author named ray tracing as path tracing.. Ray casting (1968) was simply casting rays from camera, one per each image pixel, until the ray hits the closest object. Then the pixel gets the color from the object. Ray tracing (1979) made ray casting recursive for three cases: 1. Reflection: The object surface is a perfect mirror, so we calculate the reflection angle from the incoming ray angle, and continue the process. 2. Refraction: The object is transparent, like glass. The Fresnel equations give the refraction (transmission) and reflection angles and the distribution of energy between them. For some angles, one of these can be 0. 3. Shadow ray: Shadow rays are traced towards each light source. If the shadow ray is blocked by any other object, we're in shadow in respect of that light source. If a light source is visible, both the light source color and the object surface color contribute to the color of this pixel. The object surface can also have a reflectance model (BRDF) so it doesn't need to be a matte Lambertian surface, but the BRDF is only applied to light coming directly from the light sources. An object can have partially reflective surface (like glossy plastic), and it can also be partially transparent (like colored glass). So at each intersection, we may generate up to all 3 types of rays. What we miss here, is that all surfaces diffusely reflect light to some amount, and that the colors in all diffuse incoming light from every direction contributes to the color of a surface, not just direct light from visible light sources. (We also miss caustics. Most notably, a transparent glass ball between the surface and a light source will only give a shadow in ray tracing.) Historically, there was a time when computers were too slow for sampling, even statistically weighted importance sampling, of diffuse light coming from all directions to all surfaces. So the above model of handling only 3 types of rays (mirror reflection, transparent object refraction, light directly from a light source) became both popular, and established as ray tracing. Then later, advances towards including all kinds of physically possible light rays, adopted names other than ray tracing. They are still tracing rays, but they are not called tray tracing, because the name ray tracing is understood to mean only the first method that got widely popular, with all its limitations.

leowoo91 7y ago
You almost touched photon mapping there but as long as rays start only from the screen, there is nothing wrong calling anything varying as ray tracing. Limiting reflection count or having multiple rays (monte-carlo) are often aligned with priciples you described.
- quickthrower2 7y ago
  Photon mapping? As in can render diffraction?
  - magicalhippo 7y ago
    Simplified, photon mapping is a technique where you shoot rays from the light sources and then record the hits on geometry. Name comes from pretending you're tracing a photon bouncing around. Then, when doing the regular ray/path tracing, at each intersection of the camera-ray, you see if the intersection location is near any of the light-ray hits. If so, add in some contribution from the light-ray hits. This avoids you having to explicitly check each light at each intersection point, saving you quite a number of visibility tests. Also, due to the smoothing kernel used when the "photon contributions" are added up, it leads to low-frequency noise rather than high-frequency noise that is normal in regular path tracing. This is especially noticeable when caustics are involved. A nice introduction to the technique can be found here: https://web.cs.wpi.edu/~emmanuel/courses/cs563/write_ups/zackw/photon_mapping/PhotonMapping.html https://web.cs.wpi.edu/~emmanuel/courses/cs563/write_ups/zac...