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VRay bump maps - where'd they go?
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VRay bump maps - where'd they go? // Archive: Tech Forum
Post by TheWickedWitchOfTheWeb // Jun 10, 2007, 1:05am
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TheWickedWitchOfTheWeb
Total Posts: 858
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I've got a bump map applied to a mesh. It renders fine. I turn on HDRI, the bump map does't render anymore, just a smooth surface. What, who, wah?
Is there some setting somewhere to stop VRay eating my bump maps bfore they get rendered?
Thanks in advance. |
Post by splinters // Jun 10, 2007, 3:33am
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splinters
Total Posts: 4148
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I had a Bump map applied to a texture in LW, when I switch to Vray it goes. Never mind, but when I paint the BMP onto the object (today) it keep crashing tS....:( |
Post by Bobbins // Jun 10, 2007, 10:34pm
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Bobbins
Total Posts: 506
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I've got a bump map applied to a mesh. It renders fine. I turn on HDRI, the bump map does't render anymore, just a smooth surface. What, who, wah?
Is there some setting somewhere to stop VRay eating my bump maps bfore they get rendered?
Thanks in advance.
Bump mapping relies on a trick to create the bump effect - it relies upon the direction of a light source to perform the trick. When you enable HDRI (or GI), the light source is effectively 'from everywhere' rather than a specific direction which tends cancels out the bump mapping - sometimes completely. With an HDRI image that has very clearly defined light source you can get bump maps but if it doesn't - you won't see the bump mapping unless you add a directional light strong enough to create the effect. |
Post by Misc // Jun 10, 2007, 11:37pm
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Misc
Total Posts: 59
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So in TS a bumpmap only works with direct illumination, if your mesh has an indirect illuminated side your bumpmap will work till the terminator :D
I would call this a bug! |
Post by Bobbins // Jun 11, 2007, 1:30am
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Bobbins
Total Posts: 506
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Yep that's how bump maps are - they have this inherent 'bug' built in since they need direct illumination to work, not just in tS either. You can fudge it programatically during HDRI and GI calculations by artificially introducing a direct lighting source that isn't actually in the scene just to get some bumps, but then you're not seeing 'accurate' bump maps, you are faking a fake. |
Post by Lee // Jun 11, 2007, 1:54am
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Lee
Total Posts: 13
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Interesting.
I guess displacement maps are immune to this problem, but aren't as useable? |
Post by Bobbins // Jun 11, 2007, 2:03am
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Bobbins
Total Posts: 506
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Displacement maps actually affect geometry so they are different - the bumps would be real but the object needs enough geometry to support the required level of detail.
Bump maps are only a shader effect so work on lo-poly objects. |
Post by TheWickedWitchOfTheWeb // Jun 11, 2007, 2:25am
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TheWickedWitchOfTheWeb
Total Posts: 858
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Thanks Bobbins, that explains it and makes sense.
So to use bumps I have to use a more basic light set up, or use the more advanced light set up but modell in the bumps. So to get better lighting with my clay figures I'll have to up the poly count dramatically and use displacements?
Damn! Why is life so cruel. |
Post by TomG // Jun 11, 2007, 3:24am
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TomG
Total Posts: 3397
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One option is to drop in a regular light, that will give strong directional lighting, and enable the use of non-HDRI lights with the HDRI render.
Of course, that only works where a strong directional light is suitable for the scene.
Note that Normal maps may well have a better result than Bump maps - not tested it to be sure though. Normal maps are more accurate in what they do. Bump maps say "This point on the object surface is raised to this height". It doesnt actually say what direction that point on the surface is now facing in.
Normal maps say "this point on the surface is facing in this direction", giving a more accurate description of what is happening on the surface (think of it kind of as a bump map can only make a surface point "point upward" or "point downward" in direction based on the interpolation of its height compared to other points nearby, while a normal map can make a point "point upward" "point downward" "point left", "point right" and any combo of those values).
The increased accuracy there MIGHT allow the effect to show more strongly since there is more detail and a more complex interaction with the light sources. Would be interested to know if it works out in practice :)
HTH!
Tom |
Post by Misc // Jun 11, 2007, 9:49pm
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Misc
Total Posts: 59
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Yep that's how bump maps are - they have this inherent 'bug' built in since they need direct illumination to work, not just in tS either. You can fudge it programatically during HDRI and GI calculations by artificially introducing a direct lighting source that isn't actually in the scene just to get some bumps, but then you're not seeing 'accurate' bump maps, you are faking a fake.
Sorry I don't know where you read about the limitation that you need direct illumination for bumpmaps.
Normaly bumpmaps only change the surface normals and make the shader react to the light like there is geometrie regardles of which light (direct or indirect) hits the surface. If the indirect light is stronger than the direct light, the bumpmap should change the direction. Otherwise bumpmapping would be totally useless in GI rendereres !
Regards
http://www.naha-misc.de/123/bump.jpg |
Post by Bobbins // Jun 11, 2007, 9:56pm
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Bobbins
Total Posts: 506
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In that case I look forward to your response to Witch telling her how to get her bump maps back. |
Post by Vizu // Jun 11, 2007, 10:47pm
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Vizu
Total Posts: 628
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can we agreement that this is a BUG ?
Kate ! you can try to add a other light to the HDRI scene. |
Post by parva // Jun 11, 2007, 11:09pm
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parva
Total Posts: 822
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Otherwise bumpmapping would be totally useless in GI rendereres !
:D yes indeed.
You can use bumpmaps for small or subtle elevating (think on a coarse fiber tapestry) there you will also see in real world that the side which is not lit by light will show less or even no details. The sample with the bounce light is a bit difficult because bounce light comes from "all" sides (depending on the bounce-ray strength and color) and this results in the vanishing of details or the "not visible" bump detail.
Of course there are some engines which use some tricks like Brazil with there "enhanced bump" feature.
Realistic would be that all object and surfaces have of course a geometrically substance/volume. |
Post by TheWickedWitchOfTheWeb // Jun 12, 2007, 2:39am
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TheWickedWitchOfTheWeb
Total Posts: 858
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I tried Tom's suggestion of using a normal map instead and same result, smooth surface.
Rats. Looks like uber-dense meshes and subtle displacement is the way it'll have to be done. :( |
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