View Full Version : How does Smoothing affect render times

02 February 2006, 08:10 PM
I have a robot which has 20 different surface parts. Does the object take longer to render if the Smoothing option is chosen for the surfaces?

Not a question I have thought about before, but it is annoying me so i have tried a test.

Iv rendered a single frame of my basic coloured robot with Smoothing applied to all surfaces. It took 0.6 seconds to render.

I also rendered the same object with No Smoothing applied to surfaces and it also took 0.6 seconds to render.

Is it true to say that choosing the Smoothing option does not add to render times in most cases, and if this is true could anyone loosely explain why.

02 February 2006, 09:52 PM
I'll start this by saying that I'm no rocket scientist - nor am I render programmer. But I like to think I know most things.

Having smoothing turned on should make the render slower. But by todays standards the speed difference would be negligable - it's a trivial computation relatively. If your test case ran into an hour or so, then you might see a minute or two shaved off..... but that's just a guess - probably not even that.

Darth Mole
02 February 2006, 10:07 PM
For starters, rendering a simple scene that's so quick (0.6 seconds) isn't a proper test. Try doing a scene with millions polys that takes several minutes - that way you'll see a better, noticeable difference in speeds. (For instance, one version might have taken 0.55 seconds while the other took 0.59. LW rounds up to 0.6, but there's a 7% difference).

Smoothing adds a small overhead to the rendertime, because it increases the amount of calculations LW has to perform. With smoothing off, each polygon face has the same shade across its entire face (ie, the amount of light that's hitting it is the same for every pixel contained in that poly); with smoothing on, LW has to calculate the difference in shading between one edge of the poly and another, and then apportion different values to each pixel to get a smooth gradient.

That's my understanding of Phong shading anyway.

CGTalk Moderation
02 February 2006, 10:07 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.