LWF Bug - Falloff maps wrongly corrected

[Dave_Wortley]

Create a sphere, create new material, diffuse black, reflection value 120, fresnel reflection on. Make the environment pure white for it to reflect.

Use the LWF setup with no max preferences set, vray settings gamma 2.2, linear workflow button on.

Render.. turn sRGB colour space on, looks ok? good.

Now turn your reflection value to 119.... suddenly get a horrible black void in your sphere.


Change to the max preference system for gamma 2.2 and it works fine.


Bug in 3dsmax 9 SP2 x64, Vray 1.5 SP5


Digging a bit deeper, the RawReflection is wrong in the render elements, the ReflectionFilter is fine.

[Dave_Wortley]

@Vlado, have emailed you a more concise explanation with images and max file.

[jacksc02]

if you change the cutoff value to 0 in the vray material options does that make a difference?

[Dave_Wortley]

Yes thanks this fixes the problem. Not used this option before, in what cases does it cause excessive render times? We often have material with less than 119 value reflectivity so we will always need to have this on.

[jacksc02]

In my experience I have found a very slight increase in rendertimes but thats because its rendering the whole reflection and not a "cutoff" reflection so its to be expected.

[Dave_Wortley]

Ok so perhaps Vray should look at the gamma values to stop this cuttoff value being too high? You can use script to adjust this to a smaller value than 0.1 - $.material.option_cutOff = 0.001 but still needs experiementations to work out exactly what the value needs to be, 0.003 should be fine and will save a little bit of rendertime.

[Dave_Wortley]

Anyone from ChaosGroups going to acknowledge this? We've got a work-around but this sort of thing should really be accounted for with LWF with a global multiplier or something.

[vlado]

If you use the "Linear workflow" option, it will correct any texture attached to VRayMtl, regardless if it is a procedural texture or not. Obviously, for a Falloff map, this is not what you need. However VRayMtl has no way of selectively correcting just some textures in a texture tree, and not others (for example, you may have bitmaps inside the Falloff map, or you may have a Mix map that mixes between a Falloff map and a bitmap and so on).

Like mentioned in the help index, the "Linear workflow" option is really only for quickly converting older scenes that were not set up properly. The proper method would be to either use the 3ds Max input gamma preferences, or specify the required gamma for each bitmap.

Best regards,
Vlado