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What are these artifacts?

Posted: Tue Nov 23, 2010 4:45 pm
by m-Que
Hey everyone!

I was importing some .3DS files into Studio and got some weird artifacts while rendering.
First I thought there's a problem with geometry (needed to be more subdivided), but subdividing it didn't solve the issue.
So, I gave it a shot with a few models ('Primitives') that come with Maxwell and results where the same.
Take a look at the pictures:
#1 - Sphere
Image

#2 - Knot
Image

In both cases it's just a default scene with imported primitives + physical sky.
Now, the question is: how do you get rid of those artifacts?
I tried to play with 'Smoothing', but it didn't seem to help.

Thanks

Re: What are these artifacts?

Posted: Tue Nov 23, 2010 5:36 pm
by Bubbaloo
There's only one way to get rid of these artifacts in an unbiased render engine: higher resolution mesh.

Re: What are these artifacts?

Posted: Tue Nov 23, 2010 5:39 pm
by Bubbaloo
For complex curves (curving in more than one direction), a subdivision surface (preferably subdivided at render time, like Max's Turbosmooth) is your best option.

Re: What are these artifacts?

Posted: Tue Nov 23, 2010 8:35 pm
by sampson
also try Recalc Normals in the object parameters tab if you haven't already.

Re: What are these artifacts?

Posted: Tue Nov 23, 2010 8:38 pm
by brodie_geers
I tried it out as well, and got the same results. Recalc didn't change anything. Unchecking the smoothing box obviously made the issue a lot worse but increasing the smoothing angle above the default 60 didn't do anything. I didn't have the motivation to try creating a sphere in 3ds Max and running it with different subdivisions but that seems like the next logical step. either way, it's a good lesson - i would have thought that the default Maxwell sphere was subdivided well enough to eliminate those artifacts.

-brodie

Re: What are these artifacts?

Posted: Tue Nov 23, 2010 9:35 pm
by m-Que
So, I did a couple of test, and looks like Brian was right - so far only subdividing the mesh fixed the thing.
sampson wrote:also try Recalc Normals in the object parameters tab if you haven't already
brodie_geers wrote:I tried it out as well, and got the same results. Recalc didn't change anything. Unchecking the smoothing box obviously made the issue a lot worse but increasing the smoothing angle above the default 60 didn't do anything.
Yes, tried all of that. Looks like smoothing has no effect on it.
brodie_geers wrote:... i would have thought that the default Maxwell sphere was subdivided well enough to eliminate those artifacts.
Exactly! That is why I thought there's something wrong with material or maybe some sort of bug...
And you always want keep the number of polys low, especially on a simply geometries.

Anyways, thanks for your help, everyone!
I'll make a few more tests and share 'em here, if I find anything useful.

Re: What are these artifacts?

Posted: Tue Nov 23, 2010 9:55 pm
by brodie_geers
Bubbaloo knows a lot more about Maxwell and rendering than I do, but I'm not sure it's just an 'unbiased renderers need more polygons' issue. That may be part of it, however even Maxwell does fake (/gasp...but don't worry, it does it in a physically correct way :wink: ) some smoothing where there really isn't any. I'm not sure why the threshold for that smoothing should necessarily be different between a biased and unbiased renderer. Both will give you grief if you try to smooth a box with 90 degree corners but the angle between edges on the default sphere can't be more than a few degrees or so, which should be well within the smoothing range without causing artifacts.

-Brodie

Re: What are these artifacts?

Posted: Tue Nov 23, 2010 10:59 pm
by zdeno
this conversation had place already on this forum , so just dig through previous threads . there was even good article about this phenomen. It require biased approach to solve this problem. because this "hard shaded" faces doesn,t see sun directly, so are not taken into computation I think.