Cycles - Bump map plugged to Glossy shader Normal input cause render issue

I wanted to plug a Bump to both Diffuse and Glossy shaders. But if I do that, for some unknown reason it renders only on part of the mesh.

Line across image will appear. On the left side of the image below it looks fine but on the right side it isn’t, it looks there as though it has rendered image without the Bump map plugged into the Normal input of the Glossy shader.

I discovered that the problem is caused by Bump map plugged into Normal input of Glossy shader.

It seems that the artifact is caused by the last “Add” node in the Bump map group connection which combining all free bumps together.

if I change Blend type to e.g. “multiply”, line across the image (the artifact) will disappear but all’s too much dark. Which is obvious (wrong blend type).

So why the blend type “Add” of the last node of Bump group causes this issue?

Rendered preview:

Bump node group:

I used spec map as factor of Mix shader:


Bump maps are classic *.png images with greyish background color (#b3b3b3), content in a image has dark color (#0a0a0a)

I’m using Blender v2.69

Could anyone help me with that, please?

The output from the bump node is no longer a height value, it is essentially a normal map. You can’t combine them correctly with a simple vector add operation.

If you want to go that route, some information on combining normal maps is here:

You may find it simpler to combine the bump texture maps first then feed that output into a single bump node.

You could try the vector math ‘average’ instead. Another way to go would be to combine the images first and then feed the result into a bump node. Combining images can be done with a great deal of control.

Using the Vector Math node and using Avergae works pretty well. I have tried this with successful results.

Or just combine the maps using color mix nodes before sending it through the bump node (to maximize your mixing options).