shading starter question # 1

[gaurav]

Hi Guys,

 

I am intersted in finding out how much of illuminance (that is integrated luminance over the hemisphere) is scaled on a point being shaded by a given BRDF function. 

 

Is it possible to grab this value at shading time. I find terminology /units of photomery and radiometry rather confusing in the begining and just wanted check my understanding.

 

Thanks,

-Gaurav

 

[eetu]

If I understand you correctly, Albedo SHOP is what you are looking for: http://www.sidefx.com/docs/houdini13.0/nodes/vop/albedo

[gaurav]

Thanks eetu,

seems default surface model vop has it (albido- [diffuse+glossy]) exported as "direct_reflectivity".
Which by no surpirse is the sum of diffuse + specular intensities parms.

But if i get it right, the BRDF depends on incoming and outgoing direction and gives the relative distribution of scattered and reflected light over all outgoing directions.

Now on a humble [diffuse and reflective] sphere i would expect to see varying values returned by specifc BRDF function by which all the incoming radiance (direct + indirect)to a point on its surface are scaled. which i dont find in the direct_reflectivity aov.
 

I am new to these highfalutin terms to extent of not even being sure what i am asking makes sense with that said here is my second question : 

 

2. Does Physically Based Diffuse vop implements standard lambertian model ?

 

 

Thanks,

-Gaurav