Rendering Artifacts

[KeenanCrane]

I've got two rendering problems I can't solve in this image:

http://www.students.uiuc.edu/~kcrane/artifacts.jpg

What I have is just a bunch of textured quads with a transparency map. The lower left image has the outlines of the polygons drawn over the rendering. The upper left image is the actual rendering output, and the upper right image is how it should look.

One problem is with depth of field - the renderer ignores any blurring in areas behind the polygons in the frontmost butterfly. If I watch the rendering in progress, however, this area does jitter around quite a bit from pass to pass. For the "correct" image I rendered the foreground and background images separately and composited them in Photoshop. But even doing that doesn't solve the problem - the small butterfly in the lower left which you can see through the wing of the large butterfly should also be blurred.

The other artifact is the polygon edges. It's not so bad in this rendering, but you can see a small black line on the left side of the image. I think this has something to do with using completely flat polygons, but I'm not sure what to do about it. I've tried changing the edge mode for the transparency map from wrap to repeat, mirror, etc., and tried making the texture not go all the way to the edges, but it doesn't seem to help. This effect gets especially bad when I have a low glossiness and high specularity.

Any ideas?

Thanks,

Keenan Crane
kcrane@uiuc.edu

[Wade]

Try using Clip maps to difine your butterfly rather than transparency maps. Just a guess but LW treats them differently but you should get the same effect without the Artifacts.

Wade


Maybe of some help
http://vbulletin.newtek.com/showthread.php?s=&threadid=1203

[Wade]

A Clip map removes the material.

[KeenanCrane]

Originally posted by Wade
Try using Clip maps to difine your butterfly rather than transparency maps. Just a guess but LW treats them differently but you should get the same effect without the Artifacts.

Wade


Maybe of some help
http://vbulletin.newtek.com/showthread.php?s=&threadid=1203

You're right - I used a clip map and here's what I got:

http://www.students.uiuc.edu/~kcrane/butterfly_clip.jpg

So now the area between the wings is blurred correctly. Unfortunately the butterfly showing through the wing isn't blurred at all. I'm stuck again.
It seems kind of strange that I need to do even the clipping - if I watch the rendering in progress I can clearly see all the appropriate parts being jittered around to create the depth of field effect. Why doesn't Lightwave just average all these passes together? Why does it do anything differently per-polygon?
Well, thanks for your help,

Keenan

[Wade]

Nice project by the way.

I have done my best now time for the real pros to speak up.

Wade:)

[Simon]

Hi, I always thought that Lightwave's DOF was some sort of brute force method, and it actually jittered the position of the camera around, well that's how it looks when you're watching the rendering in process! Unfortunately it appears to be based on the z buffer like other DOF methods, digital confusion, XDof etc.

This means you won't get correct DOF when looking at reflections, refractions, transparency :(

There's no solution in LW that I'm aware of, other than this workaround but it looks a bit complex! ...

http://www.altyna.com/lw/DOFreflections.htm

I think compositing is your best bet?

Hope that helps,

Simon.