# How exactly does the Strength input of Blender's bump nodes work?

From the Blender Docs:

Strength

Strength of the bump mapping effect, interpolating between no bump mapping and full bump mapping


The idea of mixing together two effects isn't new to me, it makes sense, when I say, mix a blue diffuse shader with a red diffuse shader and plug it into the Material Output, the color would be a 50% mix of red and 50% of blue, getting me a new color. I can use the Fac input to precisely control the mixing to my liking

From what I know about bump maps, we calculate the derivatives of a specific pixel on a bump map when it's mapped to a mesh to find exactly where the new, perturbed normal on a part of the mesh should point

What does it mean to interpolate/mix between no and full bump mapping logically, however? In mixing between two diffuse colors, we mix the colors. But what exactly is mixed when we interpolate/mix between full and no bump mapping?

If a specific pixel on the bump-map perturbs the normal say to the right at 100% strength, at 50% strength would it only say, perturb it half as much to the right?

How does it work with the Distance input? If the distance = 1, would 50% strength leave us with a perturbed normal that is at a distance of 0.5 ,and distance of 1 at 100% strength?

• Good question. What exactly is the difference between increasing tilt of the normal, and adjusting the height from which it is calculated? Sep 1, 2021 at 6:55
• @RobinBetts Sorry I am not sure of the answer. Also what do you exactly mean by 'height from which it's calculated'>
– Hash
Sep 1, 2021 at 7:15
• I'm just saying I would like to know the answer to your Q, too. A Bump node converts height information to normals, approximating d_height / d_tangent_x, and d_height / d_tangent_y. Often using a Sobel filter.The 'Height' field scales the height input. The 'Strength' field mixes the resulting perturbed normal with straight-up Z, I think. (Could be wrong...) But I can't work out the mathematical difference between these settings.. (I have to get the pencil and paper out :) ) Sep 1, 2021 at 7:51
• Does this answer your question? Understanding the bump node Sep 1, 2021 at 14:07