When you rotate the object 90 degrees, the Normal Map effect reverses

Development Programming & Scripting Blueprint
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The simplest, basic thing; I create a model, Bake textures, upload to Unreal, and it works, but when I rotate the model 90 degrees the concave details look convex and vice versa.

invernorm

I do not understand this.
Here are model and textures;
kostkaLowTrian.obj (32.4 KB)

Kostkav2_Albedo
Kostkav2_Albedo1920×1920 370 KB

Kostkav2_Normal
Kostkav2_Normal1920×1920 221 KB

2

Hi Yuki,

I see what you mean when saying that it looks like it’s flipping from concave to convex, quick protip. If you press CTRL + L (But keep holding CTRL after you press L) you can control your directional light. OR if you’re in the Static Mesh Viewer, just hold L and use the mouse to rotate the light around.

I took a look at this mesh+textures and the vertical axis of your normal map is incorrect.

ReferenceNormalMap.TGA (192.0 KB)

This is the Reference Normal Map, the top edge of it is purple, and the bottom edge is teal, this is the opposite of what I see in your normal map. (But on the X axis blue is on the left and pink is on the right, so everything looks as expected when panning the light over it.)

Cheers!

1 Like
3

Thanks you!
more about this here - Tutorial: Types of Normal Maps & Common Problems

Problem is;

some apps consider that the green channel should show the model as lit from below and some apps consider it should show the model lit from above. This is sometimes referred to as “normal map right-handiness”:

  • OpenGL apps (right-handed, positive green channel): Blender, Maya, Modo, Toolbag, Unity.

  • DirectX apps (left-handed, negative green channel): 3DStudio Max, CryEngine, Source Engine, Unreal Engine.

  • Substance Painter can work with both and export both types of normal maps.

Solution is;

  • invert the green channel of your normal map. Most game engines will have the option in the textures to invert the normal map, or you can manually invert the green channel of your texture in Photoshop (navigate to the channels tab, select the green channel and press Ctrl+I).

In Unreal click two times on texture in the content browser to open its config. Find and tick the box that says ‘Flip Green Channel’. This will invert the normal, in the preview, the concavities will convex, but in the editor itself and in-game everything will look right.

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