How do you use a dirtmap with a bitmap? I can’t for the life of me figure it out.
In what sense? As in a bitmap driving it or in combination with a bitmap?
Dirtmap
I have brick that I would like dirty. I want to apply my dirtmap over my brickmap. I usually render out a OA pass and multiply it in PhotoShop, but I am trying to avoid the extra work.
To use Vray dirt:::
Use Vray Comp texture-
Put your brick map in first slot-
Put vray dirt map in second slot-
Change mode to Multiply
That’s all you have to do!
Well, I’m normally using dirt in blend material
Base “clean” material (brick in your case)
-Dirt material - masked using Vray-dirt
That way I can control what kind of dirt I get. Dirt is not just darker.
In some cases it could be lighter. Like dark stone where you have dust
and sand in small angles. Sometimes it’s totally different kind of material.
Like shiny metal with rusty bumpy edges.
Dirt should be used to mask other material to wanted areas. Not
using it as color corrector etc.
Just my opinion.
(…and don’t be afraid to increase dirt samples alot. Like 100)
-LarsSon
I’d tend to do something similar larsson except I’d use photoshop for my dirt - I normally have my clean image, dirty image and then use some photoshop dirt brushes to mask between the two - You can use the masks in different ways to drive your materials quite nicely although it takes far more hand uv unwrapping and so on.
Yep, that’s really good for stills, but might be hard for animations. 
Dirt textmap in the Blurbeta plugin pack is good too.
Dirt
OK. You guys are helping, but I am getting stuck. The image below shows a box (1) and a poly (2). Both have the same material, but both are reading differently. The box (1) is a test and is working and the poly (2) is a wall that I want to make dirty. Am I missing something?
Mapping coordinates? What’s making the dirt? Bitmap or procedural? Also the poly might need some depth / shell thickness to get the dirt to work the same way.
dirt
Mapping coords was it. I thought dirt ignored mapping, but I am using a map to control the dirt so it makes sense.
I do the same thing all the time - look for a hard answer to something really easy since personally I could have never overlooked something that simple
Dirt
Now why not just put a dirt texture in the radius slot and your texture map into the unoccluded color slot? it seems to work just fine.
Dirt
Can someone take a look at this file and let me know why I can’t get my dirt to work? I think it is a scaling issue, but I can’t figure it out.
I’m pretty sure you don’t need the VRayComp Texture to get the results you want (at least for this result). Just put the brick map into the “unoccluded” map slot of the VRayDirt Texture, make sure the occluded color is still black , and you should get an identical result. It should be slightly faster (maybe not really noticeable though) since it’s a little less math for VRay to calc.
Dirt
Thanks for the feedback. I did try this, but I am not getting any effect. I’ll forge ahead and find out what I am doing wrong, if anything.