So we can characterize the incident radiance as what hits a surface and the exitant radiance as what is emitted from that surface, but what about distinguishing between light that is reflected and light that comes from the surface it is emitted from? Might we also distinguish between the light that is being emitted due to reflection and that which is being emitted as a light source? (Say, if we were trying to include a lightbulb in our image, we would want its source light to look different than the light it reflects if it is turned off, but could we have both?)
youtuyy
Incident surface radiance generally is not equal to exiting surface radiance at a point. I think it is because the energy loss happening. But do we use some ideal conditions so that the two are equal to each other for some purpose?
Staffkatamarisun
@hannahmcneil, in the final image the goal of the renderer is to produce the final sum total light from any given point in the scene, so in the end the final extant radiance will be the sum of both reflected and emitted light. Now, many renderers include ways of distinguishing "Reflected" vs "Emitted" Light, through what are known as "Light Path Expressions", which specify exactly the path some ray has taken, and will save different render passes alongside the final sum total image which include only reflected light, only emitted light, etc.
Staffkatamarisun
@youtuyy, think about the ideal condition a little. If there is a 1-1 relation between light in and light out, and at the correct angle, this is none other than a perfect mirror / reflector / metal. It can be adjusted for greater amounts of roughness, reflectance, anisotropy, etc
kevinliu64
To me the radiance in and radiance out not being equal make sense since there is going to be some type of light lost due to the material being imperfect. Unless the mirror was a perfect mirror that reflected everything. In addition, we were given a formula which specifies that irradiance at a particular point is proportional to cosine of angle between light direction and surface normal, which means energy is not being entirely conserved.
So we can characterize the incident radiance as what hits a surface and the exitant radiance as what is emitted from that surface, but what about distinguishing between light that is reflected and light that comes from the surface it is emitted from? Might we also distinguish between the light that is being emitted due to reflection and that which is being emitted as a light source? (Say, if we were trying to include a lightbulb in our image, we would want its source light to look different than the light it reflects if it is turned off, but could we have both?)
Incident surface radiance generally is not equal to exiting surface radiance at a point. I think it is because the energy loss happening. But do we use some ideal conditions so that the two are equal to each other for some purpose?
@hannahmcneil, in the final image the goal of the renderer is to produce the final sum total light from any given point in the scene, so in the end the final extant radiance will be the sum of both reflected and emitted light. Now, many renderers include ways of distinguishing "Reflected" vs "Emitted" Light, through what are known as "Light Path Expressions", which specify exactly the path some ray has taken, and will save different render passes alongside the final sum total image which include only reflected light, only emitted light, etc.
@youtuyy, think about the ideal condition a little. If there is a 1-1 relation between light in and light out, and at the correct angle, this is none other than a perfect mirror / reflector / metal. It can be adjusted for greater amounts of roughness, reflectance, anisotropy, etc
To me the radiance in and radiance out not being equal make sense since there is going to be some type of light lost due to the material being imperfect. Unless the mirror was a perfect mirror that reflected everything. In addition, we were given a formula which specifies that irradiance at a particular point is proportional to cosine of angle between light direction and surface normal, which means energy is not being entirely conserved.