     Cm = Rs - T121s ;
     for (int m = 1; m <= 2; ++m){
         Cm *= r123s;
-        Sm  = 2.0 * evalSensitivity(float(m) * D, float(m) * (phi23s + phi21s));
+        Sm  = 2.0 * evalSensitivity(float(m) * OPD, float(m) * (phi23s + phi21s));
         I  += Cm * Sm;
     }
 
     // Ensure that the BRDF is non negative and convert it to RGB
-    I = max(XYZ_TO_REC709 * I, vec3(0.0, 0.0, 0.0));
+    I = max(I, vec3(0.0, 0.0, 0.0));
 
     return 0.5 * I;
 }

    }

    // Optical Path Difference
    vec3 D = 2.0 * eta_2 * Dinc * cosTheta2;

    // Variables
    vec3 phi21p = vec3(0.0);


    vec3 xyz = val * sqrt(2.0 * PI * var) * cos(pos * phase + shift) * exp(-sq(phase) * var);
    xyz.x += 9.7470e-14 * sqrt(2.0 * PI * 4.5282e+09) * cos(2.2399e+06 * phase[0] + shift[0]) * exp(-4.5282e+09 * sq(phase[0]));
    xyz /= 1.0685e-7;

    vec3 srgb = XYZ_TO_REC709 * xyz;
    return srgb;
}

/* Polarized Fresnel Term
