[yves]

hi there

I'm just doing my first study project with maxwell. In conjunction with blowup it's possible... Render times are abit too long, I think. Well maybe in 5 years...

Anyway, I've stubled across a weird thing. Please look at the reflections of this image. Alpha is active so don't be irritated by the blackness. Still, if I postprocess this in PS this really doesn't look right, does it? Could this be because of AGS and sunlight?



best
yves

[Tim Ellis]

Hi Yves,

The reflections look correct for the normal 'Alpha' render. The secondary reflection on the left of the 'black' window, looks correct, as the left hand window is reflecting what is outside the door on the right. The strange one is the white reflection of the right hand window in the left hand window. I think the angles involved are reflecting the white wall to the left of the doorway.

One thing to remember is that a refracted hdri/mxi will show up in a strange manner, when two sets of ags or glass are overlapping visually.

So if you had a huge ags window in a building atrium, with the camera behind an interior glass balcony which covers say the bottom half of the image.
With alpha pass turned on, the huge window will render black with reflections, but where the balcony glass overlaps this window, the refractive map will be shown, not black.
However the alpha pass will counteract this when composited correctly.

For more control over reflections in post processing:-

Open the rendered image in Photoshop or similar.
Duplicate the background layer and add a layer mask.
Copy and paste your alpha into this mask.
Add your background image between these two layers.

To improve or increase the reflections, duplicate the top layer again, but this time invert the alpha mask. Change the layer blending to 'Screen' and adjust the opacity for that layer.
That will give you greater control over the reflections.

Hope this helps,

Tim.

[yves]

hi tim

thanks for your detailed explanation! that helped quite a bit
for the final compositing.

best
yves