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F1Racer
11-10-2007, 09:31 AM
Im trying to render a metal wheel rim but having some probs with sparklies that appear when rendering.

I wonder if anyone knows what causes this and how to get rid of them ?
Or even if there is another method to go about achieving the metal rim effect.

Full car shot is LW renderer (AA set to 25 passes)
Wheel shot is FPrime
My node settings are included.

F1Racer
11-10-2007, 09:35 AM
OK Ive realised now that this is happening because Im using a HDRI image as the reflection map.

toby
11-10-2007, 10:45 PM
more specifically - because the reflection of the HDR is much greater than 100% white. This causes problems because these values are much greater than the surrounding pixels which they need to blend with, via anti-aliasing.

For example, a 100% white circle on a 0% white background (black) will be anti-aliased with an average of 50% white (grey) at the edges between them, creating a soft/gradual transition, hiding the square shape of the pixels the circle is made of. If our example circle is has a value of 300%, then anti-aliasing will average to 150% white - both of which look pure white on our monitors, so there's no grey to give us that transition, and we get sparklies.

One solution is provided by a real-life event, real cameras respond to this high-intensity light with blooms and coronas that we can mimic in post or right in our 3d apps. Otherwise we need to reduce the exposure on our HDRs or reduce the reflection of our surfaces.

F1Racer
11-12-2007, 03:03 PM
Thanks for the explanation toby. I`ll note that for the future.

jayroth
11-12-2007, 03:23 PM
Just enable the "Limit Dynamic Range" toggle in the Render Globals panel (or the image processing panel). This will force the AA to assume that there are no values greater than "white" (255,255,255 or 1.0,1.0,1.0) in the render, thus properly filter the the overbright pixels.