I think you will get a better quality bloom if you just calculate the luminance instead of making dark parts black. You can calculate luminance like this: float lum = dot(color, float3(0.299f, 0.587f, 0.114f); return (float3)lum;
Then just blur it and blend with the original render like you already do.
If I try to replace the lines I got the error:
Quote: mtlBlackout(15): error X3017: cannot implicitly convert from 'float3' to 'float4' > return (float3)lum; <