Green NormalMaps - how do you make them?

[Cambridge Spy]

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?

[Springheel]

In Alekhine's Gun,

 

 

Maybe you should ask in those forums?

[Cambridge Spy]

I thought I'd ask on this forum first, see if you have experience with those.

[Bikerdude]

Nope, we only work the usual RGB normal format.

[New Horizon]

I thought I'd ask on this forum first, see if you have experience with those.

 

They're not used in the idtech4 engine, why would we?

[Cambridge Spy]

So none of you have ever seen these types of NormalMaps before?

[Arcturus]

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.

[Cambridge Spy]

Okay. Then why can't they be viewed normally on Photoshop?

[rich_is_bored]

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 March 21, 2016 by rich_is_bored

[nbohr1more]

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.

[Cambridge Spy]

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;"

[Cambridge Spy]

I've been trying to figure it out on PhotoShop. What does "Pixel.RGB" mean?