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### #ActualRPTD

Posted 03 January 2013 - 08:11 PM

That's correct. But in the case of 1cm the transparency map would contain a low value (let's say <25%) while with 10000km it would be 100% (opaque). The thickness is definitely the physically correct way to look at it but for an artist it is an unnatural material property that's difficult to handle and tune. I'm looking to understand the physics behind the problem and then to derive a PBR material property that is useful to the artist and clear to module programmers. I did the same for the surface roughness which I defined in a linear range instead of the typical exponential range as this is a lot more natural and predictable to work with while still allowing the module programmer to map it to the appropriate physical calculation under the hood.

For the transparency I want to have the same. I want the transparency to be defined in a linear way that is artist friendly while mapping to the physical representation where required. After all the absorbtion for a surface is calculated sooner or later into a transparency/coverage factor. Think of it as the final factor affecting the light color in respect to the surface color. So unless I misunderstood you the absorption leads directly to a transparency/coverage value in the range from [0..1] for the three major wavelength like transparency(rgb) = functionOfAbsorption(rgb). Since real-time rendering is anyways one approximitation stringed to the next I'm not that much concerned with a 100% accurate physical formula as this is anyways impossible. Important for me is to answer properly the question "if my colored material has a transparency of 25% (no matter what k and d value is actually required for this result using the absorption formula) how does the transmitted light ray look like?".

I'm operating here only in the flat surface situation where I have no knowledge about volume. Working for a true volume obviously is the next step like fog or liquids. That's though a different problem since there I can determine the distance and then absorption is useful and artist friendly. For a flat surface though it makes no sense and stuff like glass is typically rendered as a double sided triangle with mathetically infitesimally small thickness.

### #1RPTD

Posted 03 January 2013 - 08:07 PM

That's correct. But in the case of 1cm the transparency map would contain a low value (let's say <25%) while with 10000km it would be 100% (opaque). The thickness is definitely the physically correct way to look at it but for an artist it is an unnatural material property that's difficult to handle and tune. I'm looking to understand the physics behind the problem and then to derive a PBR material property that is useful to the artist and clear to module programmers. I did the same for the surface roughness which I defined in a linear range instead of the typical exponential range as this is a lot more natural and predictable to work with while still allowing the module programmer to map it to the appropriate physical calculation under the hood.

For the transparency I want to have the same. I want the transparency to be defined in a linear way that is artist friendly while mapping to the physical representation where required. After all the absorbtion for a surface is calculated sooner or later into a transparency/coverage factor. Think of it as the final factor affecting the light color in respect to the surface color. So unless I misunderstood you the absorption leads directly to a transparency/coverage value in the range from [0..1] for the three major wavelength like transparency(rgb) = functionOfAbsorption(rgb). Since real-time rendering is anyways one approximitation stringed to the next I'm not that much concerned with a 100% accurate physical formula as this is anyways impossible. Important for me is to answer properly the question "if my colored material has a transparency of 25% how does the transmitted light ray look like?".

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