Global illumination and final gather

[chris_swigert]

Has anyone used global illumination and final gather for your renderings. I haven't found anything posted about this and the manuals I have read are very vague. Any experience with this issue. I am more than happy to share what I know if someone is interested as well as do some experimentation together. The renderings take so long with these options that it discourages easy experimentation.

[ronie_ernanto]

Has anyone used global illumination and final gather for your renderings.
I do for final gather, but never for GI, I will try GI next time.



I haven't found anything posted about this and the manuals I have read are very vague. .
Actually I want to ask your question yesterday by I forgot to write it down.


The renderings take so long with these options that it discourages easy experimentation.

I tried to make room with 4 lights inside the room with shadow and intensity 0.2 and 1 light outside the room with shadow and intensity 0.5. With final gather set to on it make the room wall too bright. Final gather value is set to default. With Final Gather option set to on it need about to 46 mins to render than 10 mins if set the option to off. (Pentium 2.8 Dual Core and 1 GB Ram). Looks like it make the dark room brighter because the inner wall illuminated from outside light. Final gather value is set to default.

What's yours experience?

[chris_swigert]

Please know that I really don't understand either of these two commands that well and below is my attempt to tell you what I know. I fully hope and expect to be corrected in the anticipation of creating better looking renderings.

Global illumination (makes a rendering longer) - it is mostly used for interior renderings and in effect it turns all interior surfaces into light sources so that there is a sense of reflected light throughout the room and these surfaces will reflect light in response to the color of the materials on these objects they are reflecting from. Radiosity is the controlling aspect of this and I have set my radiosity on in my rendering to very high numbers (i.e. 12') because it helps to spread out these different reflecting surfaces so that they blend with one another. Otherwise, you end up with strange circles of very bright light that don't intersect. I have Photons/Light set to 30 and the energy muliplier set to .0001. I have not gotten very good looking results from this so I am looking for feedback from others. What surprises me the most is how far a lot of these settings are from the defaults.

Final Gather (makes a rendering a whole lot,lot,lot,lot longer) - I understand this command to clean up for global illumination most specifically in applications where you have a surface that starts on one side of the glass and ends up on the other. In the case where I have a mullion drawn with glass in the middle, my mullion ends up completly black unless I use final gather. I also understand that it helps in dealing with light leaks - in other words, use final gather if you don't want to model miticulously. Actually, I really don't know what this command really does.

Cheers,

Chris
Fi

[ronie_ernanto]

I only got this so far....

ID: TP8012640 - Global Illumination Hints (http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=8012640&linkID=2475176)

[chris_swigert]

Another thing I have learned to really speed up these renderings is to lower the Max. Depth, Max Reflections and Max Refractions. I think the default is 5 for these? I have lowered depth to 4, Reflections to 2 and refractions to 1. I am able to render a 1600x1200 image at presentation quality in about 5 minutes with one light and the sun on.

[ronie_ernanto]

Another thing I have learned to really speed up these renderings is to lower the Max. Depth, Max Reflections and Max Refractions. I think the default is 5 for these? I have lowered depth to 4, Reflections to 2 and refractions to 1. I am able to render a 1600x1200 image at presentation quality in about 5 minutes with one light and the sun on.

Yes, those are 5 for default.
What's your computer spec?