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View Full Version : Consistency improvements on Bump mapping generation: Search distance and amplitude.



probiner
02-25-2013, 08:53 AM
Attached a scene where there's the same image scaled down to different pixel sizes (32, 128, 1024, 4096) so you can see how each one affects the render.

So today I understood that Bumps maps' intensity in LW is dependent on the image resolution:
So for each pixel there is a search on the neighbor pixels that analyzes how much contrast there is, and therefore how much the light will be bent. Problem is that you can have the same exact image with different sizes, but since the search distance on the pixels is the same, on larger images the contrast with neighbor pixels will be minimal and the bump almost non existent.

This is very very unexpected, from a user stand-point.

I increased the Bump Amplitude and got very noisy, even though the image is very soft (???). Don't know if it is dithering or something else, but increasing MipMap to 4 seems to fix it, though in this simple example I can't account how much it affects precision.
The bump amplitude increase is proportional to the search distance decay, so if a 4096px texture does not render but a 32px does it just right, one just needs to increase the bump amplitude 4096/32*100%

Now, I asked a co-worker to test all 4 images in 3DSMax and on Vray, MentalRay and Scanline. The bump results were exactly the same (minus the decay of resolution). Don't know in other renderers, but I guess this is a LW thing.

At least here's some hint if someone gets caught on these. :)

(thanks Dave, Wolf, Sensei and zardoz for the insights)

Tobian
02-25-2013, 10:48 AM
Yes, I think this one has been known about for some time. i just wish they'd fix it :( It's possible to do, obviously, they just haven't.