the normal gets passed into the pixel shader as rgb color values (0..1) and then the _bx2 modifier brings the values into the -1..1 range. there is no way to handle the blue channel separately with _bx2.
http://www.shaderx.com/direct3d.net/tut ... ader3.htmlSigned scaling with the _bx2 modifier is a combination of bias and scale so it subtracts 0.5 from each channel and scales the result by 2. It remaps input data from unsigned to signed values. As with bias, using data outside of the range 0 to 1 may produce undefined results. This modifier is typically used in dp3 instructions. An example for this is presented with the description of the dp3 instruction above. Signed scaling is mutually exclusive with the invert modifier.