I probably should not have said it was “standard” as it seems to have a lack of one. Generally speaking, games tends to use DirectX-style (flipped green channel) normal mapping while renderers like Renderman, Arnold, Vray, etc generally use OpenGL-style normal maps.
I should also clarify that I’m thinking of this in the context of USD + MaterialX. FWIW, here’s something about normal maps in OpenUSD McUsd/unit_tests/cubes_r_normals at main · erich666/McUsd · GitHub which states that OpenGL is the “default” style normal map for USD.
Since one of the core concepts of OpenUSD and MaterialX is interoperability between DCCs (Unreal, Maya, Houdini, etc.) I was thinking that OpenGL should be the default. An example of this is the OpenChess set. assets/full_assets/OpenChessSet at main · usd-wg/assets · GitHub which if you read into Unreal needs to have the normals flipped in Y (i.e. green).
All of that to say why I was proposing that the default for MaterialX should be to assume normal maps are OpenGL style.
I am aware that you can switch to “Default Materials Pipeline” and then get all the options, including the flip normals option. However the “interchange MaterialX pipeline” does not have those options available, and defaults to assuming DirectX normal maps. When you load a USD stage with MaterialX you do not get that window.
I did try changing the Project Settings to “Default Materials Pipeline” for engine > interchange > materialX and ended up crashing Unreal (5.5). This is likely user error on my end, but if you would be so kind as to advise how to set this properly I would be most appreciative.