Color equalizer simplifications

Don't interpolate/mix where simpler maths will do it.

Author: jenshannoschwalm

data/kernels/colorequal.cl

@@ -37,7 +37,7 @@ typedef enum dt_iop_colorequal_channel_t
 
 static inline float _get_satweight(const float sat, global float *weights)
 {
-  const float isat = SATSIZE * (1.0f + clamp(sat, -1.0f, 1.0f - (1.0f / SATSIZE)));
+  const float isat = (float)SATSIZE * (1.0f + clamp(sat, -1.0f, 1.0f - (1.0f / SATSIZE)));
   const float base = floor(isat);
   const int i = (int)base;
   return weights[i] + (isat - base) * (weights[i+1] - weights[i]);
@@ -247,9 +247,9 @@ __kernel void apply_guided(global float2 *uv,
   const float2 CV = { a[k].x * uv[k].x + a[k].y * uv[k].y + b[k].x,
                       a[k].z * uv[k].x + a[k].w * uv[k].y + b[k].y };
 
-  corrections[k].y = mix(1.0f, CV.x, _get_satweight(saturation[k] - sat_shift, weights));
+  corrections[k].y = 1.0f + (CV.x - 1.0f) * _get_satweight(saturation[k] - sat_shift, weights);
   const float gradient_weight = 1.0f - clipf(scharr[k]);
-  b_corrections[k] = mix(0.0f, CV.y, gradient_weight * _get_satweight(saturation[k] - bright_shift, weights));
+  b_corrections[k] = CV.y * gradient_weight * _get_satweight(saturation[k] - bright_shift, weights);
 }
 
 __kernel void sample_input(__read_only image2d_t dev_in,

src/iop/colorequal.c

@@ -896,9 +896,9 @@ static void _guide_with_chromaticity(float *const restrict UV,
     const float uv[2] = { UV[2 * k + 0], UV[2 * k + 1] };
     const float cv[2] = { a[4 * k + 0] * uv[0] + a[4 * k + 1] * uv[1] + b[2 * k + 0],
                           a[4 * k + 2] * uv[0] + a[4 * k + 3] * uv[1] + b[2 * k + 1] };
-    corrections[2 * k + 1] = interpolatef(_get_satweight(saturation[k] - sat_shift), cv[0], 1.0f);
+    corrections[2 * k + 1] = 1.0f + (cv[0] - 1.0f) * _get_satweight(saturation[k] - sat_shift);
     const float gradient_weight = 1.0f - CLIP(gradients[k]);
-    b_corrections[k] = interpolatef(gradient_weight * _get_satweight(saturation[k] - bright_shift), cv[1], 0.0f);
+    b_corrections[k] = cv[1] * gradient_weight * _get_satweight(saturation[k] - bright_shift);
   }
   dt_free_align(a);
   dt_free_align(b);