Final Gathering And Gi

[lobopaco]

Hello everybody,

I'm currently working on a kind of a study about indirect lighting. I'm using Cinema 4D and Softimage XSI 5.0 Advanced.

While working with Global Illumination and Final Gathering, I encountered several problems. I'm sure that some of you can give me the answers I need - help is appreciated.

1. Problem Final Gathering... well, in general, it works fine. White constant sphere is around the scene; one point light with black light output. This is the initial picture I rendered:
   http://homepage.hispeed.ch/velociraptor/fg\_0\_bounces.jpg

However, when I increase the number of bounces (in order to get "color bleeding" on the floor), the details on the meshes disappear:
http://homepage.hispeed.ch/velociraptor/fg\_2\_bounces.jpg

It looks like more bounces cause more energy, so that the meshes are kind of over-exposed. But reducing the multipilier in the FG render tab only makes everything darker... Any ideas?

1. I want to obtain the same "daylight" effect using Global Illum. (photon mapping). However, no matter how many photons I cast (even tens of millions), I'm always getting a patchy image:
   http://homepage.hispeed.ch/velociraptor/Globillum.jpg

My settings are: light intensity 16 000, number of em. photons 1 800 000, no light fallof. Render settings GI Accuracy 2000, Radius 2, Photon Depth 20/20/40. I tried many many settings, always getting a noisy/patchy result. The scene is enclosed in a sphere with radius of 220 and gray phong shader.
Is there a way to get a clean result like here in Cinema 4D using the classic radiosity?
http://homepage.hispeed.ch/velociraptor/cinema\_radiosity.jpg

Thanx everybody for help/suggestions
Andillo

[deadrabbit]

Hey buddy, As for FG - are the images FG only (no GI included) if so, Have you checked the Ambience is tuned right down - this can scew up your FG/GI. Your bounces are used to take colour from each surface that is touched - as such you should not really need more than 2.
Have you used autocompute on the FG tab in the Render options?
If you are doing FG and GI check your Photon Intensity from your light.

As for your blotchy GI render - the photons are not the problem - it all comes down to your Accuracy and Radius Settings. At a guess 2-30000 photons should be sufficient. (dependant on scale).
A radius of zero, will let XSI try to autocompute the best radius for you. If you increase the Radius you should find you blur the 'blotches', and with more accuracy you get more 'blotches', play will the settings to get the best result - with a lower computation time.

Leave your photon depth for now.

You could even try deleting ALL lights and giving your sphere a incandescence - and the GI will use that to light the scene instead - It works really well!

Hope this helps-

D.

[ciaranm]

Here are some tips:
-start with direct illumination only and tweak your light intensity until you satisfied.
-turn on GI.
-Photons greater that 500,000 is usually overkill and is reserved for special situations.
-Adjust the photon intensity until you get a nice subtle secondary illumination. Try turning off diffuse on the light so that you can focus on the GI.
-In Render settings/GI start with an radius of 0 and a low accuracy (~100)
-Increase your radius and your accuracy together, slowly, until you obtain a smooth and subjectively accurate secondary illumination.
- Watch not to increase these values too high as they will greatly increase render time. Accuracy of around 800 is usually sufficient and radius is often scene dependent. If in doubt, stick with 0.
- Now turn on FG and tweak for accuracy/speed. Note: when you use GI only one FG bounce is accounted for.

For a scene like this, I would not bother with GI. FG is quite well suited for this mostly ambient illumination and will also provide bounced light from your light source.

Good luck.