bug with shadow through transparent glass material?

Feature requests, bug reports and related discussion
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CTZn
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Post by CTZn » Thu Jan 04, 2007 4:22 am

Maybe we were indeed talking about different things :wink:
Indeed.
From the above, there's clearly little or no TIR occurring at either the viewing or dominant illumination angles.
TIR is somehow opposed to the dominant illumination angle, as the result of a Reflection. The bright line between 1 and 3 is Total Internal Reflection, and the brightness of the reflect down 3 is due to TIR also IMO.
There appears to be a TIR caustic just below the glass (and one behind it) which would be the sun light entering the top of the glass and bouncing around a few times before emerging from the bottom. This looks like it's a correct TIR effect which is missing from the PT render
That's it :)
Re: tonemapping ... I don't think this is the problem, otherwise the PT render should show the same bug. I've never seen tonemapping so dramatically change the contrast of a detail when the original image isn't particularly high dynamic range to start off with.
Compare the dynamic range of an untonemapped image:

A with sun light
B with mesh light

The difference is dramatical ! Tone mapping can induce that I believe :P :D

- - - -
bidir = troubles
Mpf :? 8)

IanT
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Post by IanT » Thu Jan 04, 2007 4:27 am

Compare the dynamic range of an untonemapped image:

A with sun light
B with mesh light

The difference is dramatical ! Tone mapping can induce that I believe


I was referring to the PT render made with sun light, not the mesh light one :P :P :P :wink:

By dynamic range I meant the ratio between dimmest and brightest parts of the image. In fact, I suspect the meshlight render has a higher relative dynamic range than the sun light one (because of the black background, darker shadows etc.) but that's going off-topic now...

Ian.

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CTZn
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Post by CTZn » Thu Jan 04, 2007 4:38 am

Image

In fact, I suspect the meshlight render has a higher relative dynamic range than the sun light one (because of the black background, darker shadows etc.) but that's going off-topic now...

Off-topic ? That's the light sun gives for white, no wonder if shadows are crushed I say !

By the way isnt talking about bug which is off-topic :mrgreen: Bah I won't argue more on that for now ;-)

Cheers !

IanT
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Joined: Fri Aug 25, 2006 3:13 am

Post by IanT » Thu Jan 04, 2007 4:51 am

Trust me, tone-mapping isn't the cause of that problem, otherwise the PT/sunlight render would have shown exactly the same thing.

P.S. the "White value" for Reinhard tone mapping is an input parameter to the tone-mapping algorithm, and not an image statistic. 1e20 is a common default value. It's easy to get a HUUUGE dynamic range from an indoor scene illuminated by the sun but not so easy for an outdoor scene. I just rendered something similar to the above and the DR was only 81:1.

Anyway, tone-mapping isn't the problem :wink:

Ian.

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CTZn
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Post by CTZn » Thu Jan 04, 2007 8:25 am

Ok, I give up :)

So you think the "why" is a bug... maybe :D

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