Bump map connected to Glossy shader Normal input causes line artifact in render I wanted to plug a bump map into the normal inputs of a Diffuse and a Glossy shader. But if that is done, for some unknown reason it renders only on part of the mesh.

A line across the image will appear. On the left side of the image below it looks fine, but on the right side it isn't. It looks as if it has rendered image without the Bump map plugged into the Normal input of the Glossy shader.

Rendered preview:



Bump node group:



I used spec map as factor of Mix shader:

Nodes



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

EDIT:

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

if the Blend type is changed to e.g. "multiply", the line across the image (the artifact) will disappear. However, the resulting image is much to dark. Which is obvious (wrong blend type).

So why does the blend type "Add" on the last node of Bump group cause this issue?

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.
In short, adding all those values together is making bump values that are larger than the reasonable range.

The add nodes don't do anything magical. They are doing exactly what it sounds like ;-) They're adding numbers together. In the case of bump, full normal distortion is 1 (tallest value), no normal distortion is 0 (shallowest value).

50% grey plus 50% grey is 100% white, which is full bump distortion. 75% grey plus 75% grey is.... a color that Blender doesn't know what to do with... which is a bump distortion that Blender doesn't know what to do with.

Those add nodes shouldn't have anything to do with color. You can't necessarily expect that the color you want is also exactly the bump value that you want. You should manipulate the color of your shader seperately from the bump of your shader, even if you have to input the same image twice.

I hope this helps!