Normal Map alpha channel

Im not quite sure what the normal map alpha channel is for on these .dds files. It looks like an inverted version of the rgb map. Im currently working on a magnum texture and i would appreciate it if you could tell me what it is for.

extra:
I have not exported yet, i came here after my search turned up no results.
If this post is incomplete let me know and ill do my best to fix it.

Do you even know what the normal maps do? If you know that then what you just said would make a lot more sense.

Originally Posted by Heartview

Do you even know what the normal maps do? If you know that then what you just said would make a lot more sense.

Yes i do know what normal maps do. I am a 3d modeler and a texture 'artist'. Quite frankly, i dont use .dds as i dont do hardcore importing into games and stuff. I use a regular bmp with a standard normal map. Not this heightmap style. I dont use alpha channels on my normal maps either, only on my diffuse really.

Just to clarify i do know what all these maps do.

Diffuse : Color
Normal : bump map
Spec : shinyness
Alpha : transparency

What i dont understand is, why does a normal map (height map) need an alpha channel (transparency) and since it obviously does, what does it do.

Modeling is a little different than games, especially when it comes to CoD which uses a modified version of one of idTechs quake engines. Essentially, normal mapping would be the same as parallax mapping. Theres reasons why each is different though.

So alpha channels on height maps pretty much just determine specularity. Thats because each channel in a normal map is read differently than color files (diffuse files as you said)

MW2 style Normal Map uses Alpha channel for X axis which is left and right, whole RGB is for Y axis which is up and down, for you that means Alpha is basicly like Red Channel and RGB is Green Channel in standart style normal mapping

To see yourself - open MW2 Normal Map, copy Alpha channel to Red Channel and fill Blue Channel with white. Voila, you have standart style normal map

Normal Map alpha channel

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