bizarre bump issue

[super gnu]

wooden wall panelling, very simple material, diffuse and bump maps, both jpeg. no reflections, specular or anything.

renders fine without bump map..

buuut, with bump map.. well.. check the test renders.. looks a bit like the map is in the opacity slot or something (it isnt)

also take 3 times longer to render.


any ideas?

[vlado]

Your bump may be too strong and cause the surface normals to face the light. Does the wall have any thickness?

Best regards,
Vlado

[super gnu]

no the wall is a single face.. the bump is a standard black to white jpg..set to 30 strength... about as standard as you can get..

is it actually possible to turn the normals through more than 90 degrees with a bump map? the light is on the opposite side of the wall after all...

[vlado]

no the wall is a single face..

Then giving it some thickness will solve the issue.

is it actually possible to turn the normals through more than 90 degrees with a bump map? the light is on the opposite side of the wall after all...

No, the bump will never turn the normals more than 90 degrees, but this is not happens in your case; it is enough that the normals turn to face the light (see the drawing) and since the wall is single side, there is nothing to stop the shadow ray from reaching the light and illuminating the surface.



We could add logic to detect this case and consider the surface in shadow in both cases, however this breaks other situations where it leads to unwanted results.

Best regards,
Vlado