In much of the references that are trying to explain the GI concepts “Sample” is meaning “size of photon” that we can tweak its value using “Maximum Sampling Radius” option.
there’s another option in GI that is “Maximum Num. Photons per Sample”.
AFAK the first (Sample in “Maximum Sampling Radius” option) refers to emitting photons (actually size of emitted photons) and second (Sample in “Maximum Num. Photons per Sample” option) refers to Smoothing emitted photons; id est these are two individual steps and have’nt a same meaning.
Please let me know if I’m wrong.

Thanks..

Mental Ray User
Intel Core i7 920 @2.67GHz, 6 Gb Ram 2000, GeForce GTX 470.
Windows 8 Enterprise 64-bit.
3ds Max 2013 64-bit PU6 & 3ds Max 2014 64-bit.

Mohsen.K.

Here is how I understand it. (See Attachment, which is the default setting.)
In this case MR will define a sample radius equal to 1/20 of the diameter of the max scene. After Photons are STORED, MR begin to gather them until they reach the number of 500 (in this particular case).
In region of dense photon coverage MR will get 500 in a radius maybe much smaller that the designated 1/20 value; the sample could be much smaller.
In regions where Photons are not that many, MR will reach the 1/20 value long before the needed 500 are gathered. It’s a kind of adaptive process.
The Radius is the actual effective area of influence of any photon, the thing you are working with. MR is sampling around any photon stored on the geometry and samples are overlapping.
Activating the “Maximum Sampling Radius” box you get the opportunity to manage the process, usually going down to get a better contrast values in the rendered image.

After Photon map is saved (photons are stored) you are able to fine-tuning any settings except the “Average Photons per Light” one, because those are settings used only at render time.
The smoothing and cleaning-up is done from FG.

ivan

	Attachment

Thanks Ivan,
But 1/20 or 1/10, which is correct?

from help :

Maximum Sampling Radius
When on, the numeric value sets the size of photons. When off, each photon is calculated to be 1/10 of the radius of the full scene. Default=off, 1.0.

I think I got it BUT PROVIDED that we mean Sampling something like :
Sampling is the process of Gathering well-defined number of photons (less than Maximum Num. Photons per Sample value) in a well-defined radius (less than Maximum Sampling Radius value). I’m a simple user and not a physicist or programmer but I think photons haven’t various sizes in the real and if I don’t translate that option such as “Sampling Radius sets the size of photons” (and in fact sets the size of sampling) I’ll get my answer!

Mental Ray User
Intel Core i7 920 @2.67GHz, 6 Gb Ram 2000, GeForce GTX 470.
Windows 8 Enterprise 64-bit.
3ds Max 2013 64-bit PU6 & 3ds Max 2014 64-bit.

Mohsen.K.

Hi Mohsen,

The first question; 1/10 of the radius but 1/20 of the diameter of the max scene, or everyone is through.
The second one; you are right, photons have actually no real size they are points, entities (bundles) of RGB light energy fired from the light source. They are bouncing several times (depends of the trace depth value), by any bounce MR spawns a new photon which is a combination of the photon energy remaining after the hit and the material characteristic of the diffuse surface. At the end of the day after few bounces it (the last photon) remains stored somewhere on the scene geometry. Now the sampling story begins.
Photons have maybe no physical size but samples have and that is the radius or diameter we are speaking about. (“Globil Raduis” into the render message window.)
Samples are the entity you are working with, therefore speaking about photons we are actually meaning samples, which are those two-dimensional round areas stored on the surfaces of our models. When there are enough of them the solution is a smooth one, when not we need to fire more of them.

(PS I’m not working at Mental Images this is just my understanding of the issue.)
:)

ivan