// set up texture states 
if (grayscale) 
{ 
 ? ?device.TextureState[0].ColorOperation = TextureOperation.DotProduct3; 
 ? ?device.TextureState[0].ColorArgument1 = TextureArgument.TextureColor; 
 ? ?device.TextureState[0].ColorArgument2 = TextureArgument.TFactor; 
 ? ?// this will make out DotProduct3 operation output the luminance as the final color, see discussion for details
 ? ?device.RenderState.TextureFactor = ( 0xFF << 24 ) | ( (255-76) << 16) | ( (255-150) << 8) |(255- 29); 
} 
// render as normal