strange artificats in Pixie 2.2.5 in Ubuntu 9

[kedmond]

Today's my first day using Pixie, or any kind of rendering software.  I typically use Matlab to render all my scenes, but it's obviously very limited.

I've been trying to replicate some of the examples on the Pixie website, but have run into some problems.  Take "Ambient_occ.rib" for example.  It seems to work without any trouble, but the image quality has some issues.  There are many artifacts or severe pixelation throughout the image.

When I add more spheres to the image and zoom out to accommodate all of them in the field of view, the surfaces of the beads show strange defects or artifacts.  I tried increasing the value that is passed to "occsurf3".  While this has some effect, it doesn't resolve the problem.

The problem seems linked to both the resolution and how close the camera is to the objects.

You can see my results here:  http://kedmond.googlepages.com/3dimages

I'm not sure what to do about this.  Any help would be appreciated!

The .rib file that I used is below:

FrameBegin 1
    Format 1000 600 1
    PixelSamples 4 4       
    ShadingInterpolation "smooth"
    Display "5 beads" "framebuffer" "rgba"  # render image to buffer
    Display "+image.tif" "file" "rgba"  # render image to buffer
    Projection "perspective" "fov" 30
    //Exposure 1.0 2.2
    Translate -23 5 120
    Rotate -110 1 0 0

    WorldBegin   
        Attribute "visibility" "diffuse" [1]  # make objects visible to eye

        Surface "occsurf3" "samples" 1024

# white plane
AttributeBegin
    Color 1 1 1
    Polygon "P" [ -50 100 3    -200 -50 3    100 -200 3    100 100 3]
AttributeEnd

# sphere 0
AttributeBegin
    Color 1.00000     0.937495     0.937495
    Translate 2 1 11
    Sphere 2.4 -2.4 2.4 360
AttributeEnd
# sphere 1
AttributeBegin
    Color 1.00000     0.928233     0.928233
    Translate 5 4 8
    Sphere 2.4 -2.4 2.4 360
AttributeEnd
# sphere 2
AttributeBegin
    Color 0.973661     0.973661      1.00000
    Translate 20 25 9
    Sphere 2.4 -2.4 2.4 360
AttributeEnd
# sphere 3
AttributeBegin
    Color 2.489182     2.489182      1.00000
    Translate 30 1 5
    Sphere 2.4 -2.4 2.4 360
AttributeEnd
# sphere 4
AttributeBegin
    Color 0.942573     0.942573     0.942573
    Translate 20 20 5
    Sphere 2.4 -2.4 2.4 360
AttributeEnd

    WorldEnd
FrameEnd

[kedmond]

By the way, the artifacts or errors are not repeatable.  Every time I render this scene, the errors on the surfaces of the beads change.

-Kazem