Photon mapping...

[lilodav]

I have seen a lot of beautiful images at this forum done with photons and now I am trying to illuminate my scene with photons. But I am struggling with dark corners. As I understood the corners are controlled by Retrace threshold and retrace bounces. Retrace bounces should be equal to bounces, right? But sometimes it doesn't work. Could someone explain what the retrace threshold and retrace bounces parameters do, and how do you guys get rid of dark corners, plaese.
Thanks

[lilodav]

Why did I deserve such an ignorance?

[GoncaloP]

You can try this

http://www.vrayrender.com/stuff/PMapTutorial/

http://www.chaoticdimension.com/foru...pic.php?t=3894

Hope this helps,

Gonçalo

[dbuchhofer]

Offhand I dont know the answers, but you should look into vray.info because i know Vlado wrote a pretty detailed explanation of the photon mapping process and settings at some point in the past..

also you may want to check in the download area for the manual (if you're purchased user)

I do believe the dark corner thing is a limitation of the process though..

Best of luck..

[lilodav]

to GoncaloP:

I've been there, have read everything many times. I believe you're the one who knows photons best (seen your images and those beautiful corners), may be you could enlighten me how you get rid of dark corners, also what the retrace threshold and retrace bounces parameters do? Besides I've noticed that photons are units dependant and what works for you just doesn't work for me (I have tried your scene and changed the units to inches). That's why I am tring to UNDERSTAND the parameters, I don't need any ready solution to follow. You guys are the only hope.
Thanks in advance.

[GoncaloP]

The only way I found to get ride of the dark edges was to build a very strong photon map base shooting a very high amont of photons, that is what the test scene is about.

I use to play with retrace treshold at 0.0, because seems that, in this way its easier to get photons in the corners but, at some point of his photon map tutorial, Vlado says that "photon map provides a good approximation only for surfaces that are far away. Near corners, the noise of the photon map will bias the solution, giving rise to these artifacts. This can be solved by computing GI with Monte Carlo methods instead of the photon map near corners. The Retrace threshold parameter controls what "near corners" means to VRay. When it is 0.0, no retracing is done. Higher values will cause more retracing and will slow things down. Return the Retrace threshold to its default value of 2.0."

In the new Vray Manual you can look for better explanation of all the other settings means, however it says that max density "allows you to limit the resolution (and this the memory) of the photon map. Whenever VRay needs to store a new photon in the photon map, it will first look if there are any other photons within a distance specified by Max density. If there is already a suitable photon in the map, VRay will just add the energy of the new photon to the one in the map. Otherwise, VRay will store the new photon in the photon map. Using this options allows you to shoot many photons (and thus get smoother results) while keeping the size of the photon map manageable."

You will need to find what are the values that works for your scenes based in your scene units.

Hope this helps you, good luck

Gonçalo

[lilodav]

RE: "The only way I found to get ride of the dark edges was to build a very strong photon map base shooting a very high amont of photons, that is what the test scene is about"

So as I understood I need to put very high value in diffuse subdivs of the light?

RE: "max density "allows you to limit the resolution (and this the memory) of the photon map"

So what is the highest max density? Zero? If zero - the memory usage will be the highest? Gotta give this a try, hope lots of photons will help with dark corners...