use a logarithmic brightness adjustment instead of a linear divider

peterzuger · Mar 23, 2021 · a4fdc4d · a4fdc4d
1 parent 6a908a9
commit a4fdc4d
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Showing 3 changed files with 42 additions and 3 deletions.
diff --git a/tlc5947/color.c b/tlc5947/color.c
@@ -120,6 +120,45 @@ rgb12 rgb8torgb12(rgb8 c){
     return _c;
 }
 
+static const uint16_t logLUT[2][12] = { {
+        0,  353, 1109, 1990, 2614, 3495, 4120, 5000, 5775, 6990, 8495, 10000},
+      { 0, 1500, 4000, 6000, 7000, 8000, 8500, 9000, 9300, 9600, 9800, 10000 }
+};
+
+static float log_brightness(float f_linval){
+    uint8_t i;
+    uint16_t ipf;
+    uint16_t linval = (uint16_t)(f_linval * ((float)10000));
+
+    if(linval >= logLUT[1][11]){
+        ipf = logLUT[0][11];
+    }else{
+        for(i = 0; i < 11; i++){
+            if(linval < logLUT[1][i]){
+                break;
+            }
+        }
+
+        ipf = (linval - logLUT[1][i - 1]) * 10 / (logLUT[1][i] - logLUT[1][i - 1]);
+        ipf = logLUT[0][i - 1] + (logLUT[0][i] - logLUT[0][i - 1]) * ipf / 10;
+    }
+
+    return (float)(((float)ipf) / ((float)10000));
+}
+
+
+rgb12 rgb12_brightness(rgb12 c, float brightness){
+    rgb12 _c;
+
+    float b = log_brightness(brightness);
+
+    _c.r = (uint16_t)((float)c.r * b);
+    _c.g = (uint16_t)((float)c.g * b);
+    _c.b = (uint16_t)((float)c.b * b);
+
+    return _c;
+}
+
 void default_white_balance(white_balance_matrix m){
     for(uint8_t i = 0; i < 3; i++)
         m[i] = 1.0;

diff --git a/tlc5947/color.h b/tlc5947/color.h
@@ -77,6 +77,8 @@ rgb8 rgb12torgb8(rgb12 c)__attribute__ ((const));
 
 rgb12 rgb8torgb12(rgb8 c)__attribute__ ((const));
 
+rgb12 rgb12_brightness(rgb12 c, float brightness);
+
 void default_white_balance(white_balance_matrix m);
 rgb12 rgb12_white_balance(rgb12 c, white_balance_matrix m);
 

diff --git a/tlc5947/tlc5947.c b/tlc5947/tlc5947.c
@@ -346,9 +346,7 @@ static bool pattern_do_tick(tlc5947_tlc5947_obj_t* self, pattern_base_t* pattern
 
             pattern->brightness = clamp(pattern->brightness + p->brighness.brightness, 0.0F, 1.0F);
 
-            pattern->color.r = (uint16_t)((float)pattern->base_color.r * pattern->brightness);
-            pattern->color.g = (uint16_t)((float)pattern->base_color.g * pattern->brightness);
-            pattern->color.b = (uint16_t)((float)pattern->base_color.b * pattern->brightness);
+            pattern->color = rgb12_brightness(pattern->base_color, pattern->brightness);
 
             pattern->current++;
             if(pattern->current == pattern->len)