Negative colors in displacement map using <UVTILE> extensions.

[ilpvfx]

Hi!

I'm having trouble getting negative values in a displacement map to displace correctly when working with the <UVTILE> extension in the file node.

I'm using a 32-bit exr checker texture with a range from -1.0 to 1.0. When I use a single file the negative values of the map are displaced correctly. When I'm using the <UVTILE> extension the negative values of the map gets clamped.

I have checked "Allow negative colors" in the Extra VRay Attributes on the file node.

I first noticed this problem when using displacement maps exported from Mudbox but I get the same problem using this checker texture created in nuke.

I'm using sing Vray 3.10.01

Is there a way to get around this problem?

Cheers!

[vlado]

Add V-Ray displacement control attributes to the mesh and turn on the option for explicit displacement bounds where you can manually enter a min and a max value:
http://docs.chaosgroup.com/display/V...cement+Control

When you use a single OpenEXR file, V-Ray can find out the correct bounds automatically, but there is no way to do this for multiple UV tiles.

Best regards,
Vlado

[ilpvfx]

Ah, I see!

Thanks a lot!

[tr3c00l91]

Hey guys,

I have this problem as well and I couldn't fix it.

I didn't know how to get my general min/max values from my map (exported from ZBrush) as well as how to put these values in the "min value/max value" option.

So I opened my 32 bit Displacement exr in Photoshop and picked the highest and the lowest parts and saw that it hat a value of about 4. So a changed the color to RGB 1-256 and put 4 and -4 in the red/all channels but it didnt change anything. So how can I put the 4 in max value? :/

And do you know how I can get my min/max values from my displacement map?

[vlado]

I usually set the color picker needs in 0-1 mode, and then try different values (line -10/10, or -50/50) until I find one that works.

Technically we can write a command-line tool to print out the min and max values from a map, maybe we could extend the img2tiledexr tool to do it.

Best regards,
Vlado

[tr3c00l91]

aaaah, now I get it. So you don't have to put the exact values in just some more or less fitting ones?

It works now! Thank you so much for your quick reply.

And yes, that function would be a nice feature!

[vlado]

aaaah, now I get it. So you don't have to put the exact values in just some more or less fitting ones?

It doesn't have to be exact, it can be bigger (but not smaller, smaller values will truncate parts of the displacement). The effect on the final render is that V-Ray may think that the displaced object is larger than it is, and tessellate it sooner than needed but in many cases it doesn't matter.

Best regards,
Vlado