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In Blender Bump Node what color is the neutral position (no bump).black, white, or 50% grey? and what is up and what is down?

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  • $\begingroup$ Yes - 0.5 grey is "middle" anything whiter is "up", anything blacker is "down". The more white, the more "up" - the more black, the more "down" $\endgroup$ Jan 19, 2023 at 15:48
  • $\begingroup$ But that's not really the best way of thinking about it - there really is no "neutral - it's more based on relativity. If one section is lighter than another, it will be considered "up" compared to it - how much "up" is dependent on how much difference there is between the 2 shades. The range is between 0 and 1 so the "height" difference between 0.5 grey and 1.0 white would be less than if it was between 0.0 black and 1.0 white. BUT.... if you want the bumps to go "up" AND "down" (have an equal amount of "swing" on both sides), it is easiest to think of 0.5 grey as the "middle". $\endgroup$ Jan 19, 2023 at 15:58
  • $\begingroup$ Also considering Blender shader editor is color managed, 50% grey may not equate to an actual 0.5 value. $\endgroup$ Jan 19, 2023 at 16:48
  • $\begingroup$ @DuarteFarrajotaRamos The Shader Editor is color managed, however the Height input of Bump and Displacement nodes are using float values. Which means the resulting height is not dependent on the color management. It is hard to tell for bump, but using it with displacement you can simply verify it with the resulting heights (see my much too long answer on this topic). $\endgroup$ Jan 20, 2023 at 10:41
  • $\begingroup$ @GordonBrinkmann Ah, true, my mistake. The issue is probably different, maybe its the color gradient using logarithmic scale, rather than linear, that explains why a 50% gray is not at 0.5 value. $\endgroup$ Jan 20, 2023 at 10:56

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The Bump node is a bit tricky as it is not really creating displacement, but just the illusion of subtle surface displacement. So if you are asking for a "neutral" position it depends on what reference you want to use to base your "neutral" position on. Also it's sometimes hard to see in varying lights and angles if there is bump and if it goes up or down. Just a general information, as Christopher already mentioned, black or 0 is always the lowest point and white or 1 the highest - but this is all in relation to the bump texture itself. This is independent from surrounding faces with different textures.

In the following example I have a plane with two materials: a base material with a simple Principled BSDF and a bump material - which has the exact same Principled BSDF but also some bump information plugged in the Normal input.

This is the bump part of the material:

bump material

In the following image you can see the bump texture on the left, it is a black square with a 0.5 grey circle in the center and in it a smaller full white circle. The surrounding light blue is the base material. In the middle you can see the effect the bump has, the light reflections make it look like where the bump is grey it is slightly raised over the black bump part and the white is a slight elevation on top of the grey. And the other thing you see, especially on the right where the sun's reflection hits the camera in a different angle, there is no seam between the base and the bump material. So, it seems black is neutral in relation to surrounding textures, right?

bump effect

Well, no not really. Take a look at the following image - I switched the grey and black areas as you can see on the right, and in the middle you see that now the bump seems to be slightly lowered where the black part comes and then raised again where the white is. However, as you can see on the right, although black is no longer at the border to the base material, there is still no seam visible. So in this case grey is neutral to the surrounding. And it would be the same if I would make it white on the outer part. (Also notice how the optical illusion can change with the viewing angle - the view on the right is hardly different to the previous one, no matter if raised or lowered.)

bump with grey border

And now you might think as long as the bordering color is the same all around, it will always be neutral to the surrounding... but not even that. If I now take a Gradient Texture set to Linear, I have black, grey and white on the border to the surrounding material. But although the bump shows the correct raise from dark to bright, there still is no seam visible between the bump and the base material. So each color is neutral in relation to surrounding materials without bump.

bump with linear texture

As you see, the Bump node is quite tricky since it doesn't create real geometry but just the illusion of displacement.

Just for completeness: where it actually makes a difference and you also have a "neutral" color is when you have real displaced geometry with the Displacement node. I'll take the bump material but instead of using a Bump node, I'll put the texture into the Height of a Displacement node and plug it in the material's Displacement output.

displacement node

I need to mention, the following values and functions are all based on objects that have their scale applied. So, with the black square and the grey and white circle plugged into the Displacement, the result looks like this:

default displacement

The Displacement node is set to its default values of Midlevel = 0.5 and Scale = 1. The Midlevel value is giving the offset of the displacement values towards the surrounding undisplaced geometry. Don't know how to say it better, but this is how it works:

Let's say the plane with the base material has its faces at a height of Z = 0. The Midlevel of the displacement is set to 0.5, which means a value of 0.5 is at the height of the undisplaced geometry. Values to displace that differ from the midlevel are placed at

$$Z = scale·(displace - midlevel)$$

which in case of complete white means

$$1·(1 - 0.5) = 0.5$$

so the displaced part is at a Z height of 0.5 m, whereas black values are at

$$1·(0 - 0.5) = -0.5$$

which is -0.5 m down on the Z axis. And as you can see in the image above that is exactly what you get. The grey part corresponds to the mesh being at the same height as the undisplaced geometry, the white part is at 0.5 m and the black at -0.5 m.

If you now change the midlevel to 0 it means, black is at the level of the base material and every value above 0 is raised above the ground, so grey is at 0.5 m and white at 1 m, whereas changing the midlevel to 1 will only let pure white be on the surrounding surface and all values lower are creating a hole in the ground, with the grey at -0.5 m and black at -1 m:

varying midlevel

The last image is just to show the influence of the Scale value in the Displacement node. When set to 0.5 for example at a midlevel of 0.5, the displacement does not range from -0.5 to 0.5, but from -0.25 to 0.25 since the values are multiplied with the scale factor. Very important for the result: first the difference between displace value and midlevel is calculated and afterwards it is multiplied by the scale, not the other way round.

changing the scale

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