I have a material I am creating that has a bump map and I am trying to add grunge to the edges of the holes created by the bump map, any ideas how I could achieve this? thanks for any help you can offer.

here is the bump map

I want the grunge to be along the lines and around the edges of the darker portions

  • $\begingroup$ Could you post your bump map and show where you want to have grunge there? $\endgroup$
    – cgslav
    Aug 1 '17 at 11:28

It propably depends on the geometry you're working with, but you might have a chance in abusing the fact that normal maps are indeed just encoded direction vectors, which are assigned to the R, G and B color slots. If you try a node setup like this (so feeding the normal output into an emission shader and previewing that) on your texture...

check normal maps

... you'll see the famous mostly blue normals texture:


Add two more nodes afterwards to split up the three channels into its components. One is a SeparateRGB node, the other one an invert node. You'll need the invert just on the B channel, not on the other two:

split up channels

The result of that separation will be this:


Whereas the original texture which I was feeding into the whole chain was simply this:

orginial Texture

The background is, in the R channel or a normal map, the perturbation amount of the normal in U direction is stored, whereas in the G channel the V perturbation is recorded. B is - I believe - a factor of how unperturbed the normal is. That's why you need to invert it, as you're interested in the bumpy areas only.

With your provided texture, the setup produces this:

used on orig texture

  • $\begingroup$ Late to the party, but this is an incredible answer. This method actually works better on the baked out normal than the pointiness from the geometry node did on my high poly! $\endgroup$ Feb 22 '18 at 16:13

You can use bump maps for this. The node setup I used is enter image description here Notice how I used the same image twice; both for the texture and the bump map.

Without bump map: enter image description here

With bump map: enter image description here Open the images in full view to view the details

Hope this helps.

  • $\begingroup$ i was wondering how to add grunge to the edges, not how to use bump maps, sorry if I didnt convey this clearly. $\endgroup$
    – Chris Howe
    Aug 1 '17 at 18:37
  • 1
    $\begingroup$ Ah (Not a native English speaker, so had to google "grunge"). You can achieve this with multiple methods. The easiest would be to use your texture. Blur it with nodes, invert the colors, and use it as a mask texture for your grunge. I can't show an example right now since my cycles is messing up, so have to troubleshoot that. But I'll see if I can edit my answer when I get it fixed if no one else beat me to it. $\endgroup$
    – FreemoX
    Aug 1 '17 at 18:41

In the case of the bump map you provided, I would simply run an edge-detector over it in an image editor of your choice and then alter the generated texture (blur etc) to suit the look you are going for. This is obviously not a procedural solution and does not behave the same way as the pointiness-input, but it can provide a similar effect.


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