dolphin/Data/User/Shaders/grayscale2.txt

uniform samplerRECT samp0 : register(s0);

void main(out float4 ocol0 : COLOR0, in float2 uv0 : TEXCOORD0)
{
  float4 c0 = texRECT(samp0, uv0).rgba;
  // Info: http://www.oreillynet.com/cs/user/view/cs_msg/8691
  float avg = (0.222 * c0.r) + (0.707 * c0.g) + (0.071 * c0.b);
  ocol0 = float4(avg, avg, avg, c0.a);
}