I am studying Monte Carlo Path Tracing from different sources. However, I have some confusion about the
sampling part and dare to post here for experts' clarification.
Most of the sources present path tracing as figure below:
This represents, the light ray starts from the camera/eye, has 3 bounces (whatever is the predefined bounce number), and then hits the light source (
L_e >0). If I am not wrong, when a ray hits the surface, it has surface information like
material. So if it hits a diffuse surface, it will flow the output angle wrt. the normal anywhere in the scene until the next hit (below figure).
I assume in this figure above, I have one sample per pixel, and that sample is traveling throughout the scene (the deep orange color ray). The rest of the 5 rays are randomly generated reflected rays over the hemisphere (point
P in the above figure).
Question: Can I call this one primary ray to 5 other reflected ray creation
ray splitting? How do I define these 5 random
splitting? Is it the
hemisphere sampling? with some pseudorandom number generation like
Now come to the second confusing point, according to
pbr book, each sample is a complete path in the path tracing algorithm. If that is true, according to the first figure, I am just shooting one sample (one path) like below. but the first figure shows I am actually creating
6*6*6 =216 paths within 3 bounces. How that could be possible?
Now, if I shoot multiple samples per pixel, like the figure below, I guess that should follow some pattern as well (lets say, adaptive sampling)
Now, instead of shooting at a point, the
light rays will hit in a similar area and finally the average the
final color value.
Question How this
pixel samplingis different than the hemisphere sampling?
My whole understanding is like this, I guess if I shoot 5 primary rays, they will hit the surface in 5 different points (similar area), and reflect according to the material and attenuation. However, I need to create
hemisphere sampling separately for the hemisphere and determine, how many random points I am going to create over the hemisphere. Am I right?
Instead of these two types of sampling, I also see there are
light sampling, etc. Is there any other type of sampling?