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Alpha in normal maps not working

I'm pretty sure this worked in UE3 and in UE4 it shows that a normal can have alpha with "Has Alpha Channel: True" but it is always just white. So I'm guessing this is a bug and not a limitation.

Product Version: UE 4.8
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asked Jul 04 '15 at 11:39 AM in Bug Reports

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Davision
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Hi Davision -

The Default Compression format for Normal Maps in UE4 is BC5 which does not retain Alpha information, hence the white value when you look at the Alpha Channel. You can adjust the Compression which you use on the Normal Maps to VectorDisplacementmap which will allow you to reallocate some bytes from the Red and Green Channels to generate an Alpha Channel with some minor loss of quality to the Normal map. You will also need to change the Texture Sample in the Material to use Linear Color as opposed to Normal Map.

I have put in a feature request to add the NormalMapAlpha compression that would allow you to keep the NormalMap compression (Probably forced to DXT5 and not BC5) and an alpha channel, for reference UE-18196.

Thank You

Eric Ketchum

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answered Jul 06 '15 at 04:15 PM

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Lovecraft_K ♦♦ STAFF
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avatar image 00k_ Aug 13 '16 at 11:40 PM

Was this issue ever resolved? It still seems like there's no way to have a normal map with alpha and using a vectordisplacement map is not realistic given it's uncompressed.

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