Inaccurate AO shadows under glass [solved]

[R Reynolds]

This issue may not be fixable if it's an unavoidable side effect of how AO works but I'll submit it anyway.

Here is a prog. render of the test model illuminated by a sun type light source. The model is a flat grey surface above which hovers four glass windows. Each window model (7 in. x 7 in.; 17.8 x 17.8 cm) is 4x4 patches surrounded by a tubular frame. The greenish glass has a 90% transparency. Each window is floating a different distance above the grey surface ranging from 2 in (5.1 cm) to 1/2 in. (1.3 cm).

This is a final render(9 passes) of the model after you turn on AO = 100% with a sky blue global colour. Notice that the ambient light is still being partially blocked by the almost transparent glass and the shadow density increases as the glass gets closer to the surface. If you reduce the transparency of the glass, the density of its ambient shadow increases so clearly AO is sensitive to the surface transparency. But even at 100% transparent the glass still has a noticeable ambient shadow when its very close to another surface. 

Even stranger is a progressive screen render with AO on.

This also happens in v19p. Embedded project is attached.

AO_bug_v19pt5a_embed.prj

[robcat2075]

I wasn't able to load the PRJ because it is calling for several image maps. Images are always external to the PRJ file.

However... first... do you have Transparent AO turned ON?

 

If you already had that ON, can you make a version that needs no images, or otherwise, attach the images here?

[robcat2075]

v18 handled the missing images more elegantly, so I did this render in that.

Yes, I think turning "Transparent AO" ON will get you the result you are looking for.

[R Reynolds]

Right you are Robert!  Thanks. I'd long forgotten about that option. After turning it on I didn't notice that the render was noticeably longer, so it it stays ON by default. Sorry about the missing images, they were a holdover from my original test for believable female eye-lashes which started this whole thread.