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Green NormalMaps - how do you make them?


Cambridge Spy

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In Alekhine's Gun, the NormalMap files for textures cannot be viewed normally with Photoshop and you have to open the .bmp files as a .dds. They're green instead of purple. How do you make green NormalMaps and how can you make them openable in their original .bmp format?

post-33055-0-29820200-1458561509_thumb.jpg

post-33055-0-84074600-1458561513_thumb.jpg

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I know of tangent space, object space and world space normalmaps and that doesn't look like any of them. However, this could be just a green channel of the normalmap. (Just checked) yep, looks like a green channel of the normalmap alone.

It's only a model...

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The thing to keep in mind is that a normal map isn't purple for the sake of being purple. Each color channel represents a different component of a surface normal. They aren't photos.

 

The image posted seems consistent with what you'd expect to find in the green channel of a normal map. You need to identify where the missing components are being stored. Maybe the original file has an alpha channel and data is being stored there?

Edited by rich_is_bored
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Also. many new engines pack normals in unusual ways to conserve on g-buffer space (for example). Usually that is done on-the-fly

but it wouldn't surprised to see some strange dev pre-process their data to match it's buffer representation somehow.

 

DDS is a container format, which means that it could be anything from DXT1 to DXT5 or even could be something custom packed in there

via format abuse.

 

Now that I think of it, RGTC compression (Red Green Texture Compression) (which is DXT5 alpha with a weird data arrangement)

or Luminance compression (LATC \ 3Dc ) would probably look like that.

 

https://www.opengl.org/wiki/Red_Green_Texture_Compression

 

Don't know any tools that are good at decoding it to RGB though.

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I asked about them on the Haggard Games forum, this is what I got from Alexey:

 

"Well, normal maps stored in "compressed" format. You will have to decompress them to make it look like regular normal map. There is only X and Y stored in DDS file. Z computed in real time.
Final normal will be:

Normal.X = TextureDDS.Alpha * 2 - 1.0;
Normal.Y = TextureDDS.G * 2 - 1.0;
Normal.Z = sqrt( 1.0 - Normal.X*Normal.X + Normal.Y*Normal.Y );

To convert back to regular normal map RGB values:

Pixel.RGB = Normal.XYZ * 0.5 + 0.5;"

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