• Shaders importing normal map images must be vector3, and not color3.

• Feed images from a Mtlx Image through this node, and into the normal input on Mtlx Standard Surface

The normal map node takes the input normal and transforms it by the basis that’s formed by the shading normal, tangent and bitangents. However, when dealing with MikkT tangent space normal maps, you have to consider several things. There’s a recipe to add the karma_mikkt shader property. You can execute the recipe when you right-click the node and choose Recipes ▸ Karma MikkT Normal Map.

This property indicates that the tangent space normal map input should be treated as a MikkT tangent space normal map. In this case, the tangentu and signs attributes/primvars will be used to properly define the basis. If Karma MikkT Normal Map is turned off (or not present), or the tangentu primvar doesn’t exist, then the map is interpreted as a Karma-specific tangent space normal map (if the signs attribute/primvar isn’t present, it will default to -1).

• For a Karma-specific tangent space normal map, Karma will use it’s default tangent shading frame to apply the normal map operation.

• To make Karma-specific tangent space normal maps work in Houdini VK, the tangentu primvar must exist. You can create the primvar through the Poly Frame SOP. There, choose the Tangent UV Gradient style. Then use a Geom Prop Value to read that primvar, and wire it into the tangent or geometry_tangent inputs on your surface shader.