Radiosity - Help Me!

[3DeeNut]

I need help and ive exhausted myself looking for a solution... now i have to ask the pro's on this board for some tips...

Ok, problem is this. I have this car scene and I am trying to get a good radiosity render of it. Unfortunately I am getting a heavy "grain" effect and I cant get it out no matter what I do. I have wanted to use HiDri Images for the lighting, but as I could find no HiDri images i just set my lighting to a dome (inward polys) lighting situation and used a procedural gradiend for tonal variation. I dont think thats the problem but you should know all the facts. Ther scene looks ok, but i really need the car paint to be "slick and wet looking" not grainy like it does. Any help would certainly be appreciated.


Also, I am getting wickedly high renders using monte carlo (this 640x480 took over 24 hrs on a dual 2.0 g5 with 2.5gig mem)... If this keeps up I am gonna be fired from my job lol.

[kopperdrake]

Oof - not sure this'll help but if you're serious about using radiosity at the moment then get FPrime - it'll save you loads of time for such scenes. The way I do these shots is to make a backdrop colour all-white, then add fog (same colour as backdrop colour) - then you don't need a lighting dome as this will work in radiosity.

This will give you your subtle shadows, but to get those lovely lines you needs some props. I use large white boards with 100% luminosity and 0% diffusion. These need placing in your scene so your car's reflectivity will pick them up and you can see them in the paint. You may need to turn off the objects' attributes so they're not seen by radiosity as they're going to act as large lights, which you may or may not want.

There may be other more graceful ways but that's how I've done it in the past.

Ah - You may as well use background radiosity as well - your scene is not really complex enough to warrant full on radiosity :)

Cheers,

Dunk

[3DeeNut]

Ok, I found the killer of my rendering times and crteator of those "splotches". It was in fact the problem of using a procedural texture as the luminosity map. I ended up downloading a decent sky texture and used it for this scene. My render times went from over 24 hours to 8 minutes (much more liveable). I also switched radiosity type to backgraound as suggested. Its starting to shine. I did know about the props (i used them in my avatar) but i am going for a very out doors salt flats kinda look so im not sure it applies in this case.

This is what ive got so far... continued suggestions are appreciated.

could you elaborate on the fog idea though?

[3DeeNut]

Just did some post production on this....

[kopperdrake]

Ah - if you're after the salt-lake thing then the fog idea won't work as it's mainly a way I do stuff that's meant to look like it's been shot in a studio. You just set the backdrop colour to white (in the Backdrop tab in the Effects panel (F5)). That will essentially light your scene from all angles with the white light, assuming radiosity is being used, but if you have a ground object then that will prevent the white from shining upwards. The sky dome can also interfere with this so don't let it cast shadows. You then just turn on the fog in the Volumetrics tab in Effects panel and enable 'Use Backdrop Color' - that will make a fog that is the same colour as the backdrop.

You can see examples here:

http://www.albino-igil.com/blog/?p=8

This technique would have been used in the studio shot, but for the salt-flats image I used about 20% fog, a sky dome (as you have done, but make sure it only wraps once as yours seems to be a bit distorted). The mountains were modelled using DEM data and satellite imagery and the ground was texture mapped.

Typically I set radiosity so it gives me the shadows I want, but the image looks about 50% of the final brightness I want. I then add an area light to bump it up to the final brightness. This gives a nice sharp shadow that the sun would give in such a scenario.

Hope this helps :)

Dunk

[Exception]

Far fast and smooth radiosity, you can also try interpolated. Its faster than background, and can be smoother, but it can flicker in animations, its therefore much better suited for stills. If you're rendering a still, and not an animation, and want fast and smooth radiosity, set you AA to PLD 5, or classic low, or higher, and turn on motion blur, even if nothing is moving. That way the radiosity calculation is redone each pass, and will be overlaid and you will get very smooth results.
I usually start of using 0.9 as tolerance, a decent number of rays (doesn't matter as much with 0.9 tolerance), and the standard spread. You can even quickly preview 3 bounce renders this way.

But yes, fprime is awesome, totally and utterly fantastic.

[3DeeNut]

Thanks All, Il post my results tomorrow or the day after when i get some more finished looking stuff.

Seriously, thanks!