3d displacement clips exr

[Morbid Angel]

" - Note that with 3d mapping the displacement map's range of values must be within the 0.0-1.0 range (black to white). Values outside of this range will be clipped. "


So I have read in the manual that a 3d mapping in vray displacement mod will clip any float to 0-1 range. We are using exrs for displacement maps and are having an issue with that. Is there any way to solve this?

[vlado]

You can scale the output of the .exr so that it is within the [0-1] range and multiply the displacement amount proportionally to keep the effect the same.

For example, if the maximum pixel value in the .exr file is 10.0, set the RGB Level of the texture to 0.1 and multiply the displacement amount by 10.0.

Best regards,
Vlado

[Morbid Angel]

You can scale the output of the .exr so that it is within the [0-1] range and multiply the displacement amount proportionally to keep the effect the same.

For example, if the maximum pixel value in the .exr file is 10.0, set the RGB Level of the texture to 0.1 and multiply the displacement amount by 10.0.

Best regards,
Vlado

so could you explain why vray does that clipping inthe first place? does the same happen in mr?

[vlado]

mental ray clips at a user-specified boundary; there is a parameter for this somewhere.

The clipping is necessary because V-Ray (and mental ray, and PRMan) needs to estimate the bounding box of the displaced object, so that it can be fit into the acceleration/occlusion structures. For this reason, the renderer needs to know a maximum extent for the object. To calculate that extent, V-Ray must know the maximum possible value of the displacement function. In 3ds Max, V-Ray simply assumes that the maximum is white. In Maya, it is more intelligent and can guess this value from the .exr file itself.

Best regards,
Vlado

[Morbid Angel]

you know what im going to ask for next
could you implement a value clipping so that it can be adjusted like in mr?

[vlado]

A specific option would be nice, I agree, but for now by tuning the output amount of the map and the displacement amount, you are doing effectively the same thing.

Best regards,
Vlado

[Morbid Angel]

A specific option would be nice, I agree, but for now by tuning the output amount of the map and the displacement amount, you are doing effectively the same thing.

Best regards,
Vlado

thanks good to know that. The reason Im asking this is we output displacement maps out of mudbox as 32 bit exr. In theory you just apply the displ map without tweaking any amount values and if your scale is correct then you get displacement as it is in mudbox.
This works exactly like that with 2d mapping, but as you know we are forced to have multiple material face ID, so we have to use 3d mapping and there is the limitation.
What we have done is actually rescaled the exrs in photoshop, but its an extra step, with already too many extra steps as is.