Changed gamma correction to adaptative resolution from 8 to 11 bits

sonoff/xdrv_04_light.ino

@@ -102,23 +102,70 @@ struct LCwColor {
 const uint8_t MAX_FIXED_COLD_WARM = 4;
 const LCwColor kFixedColdWarm[MAX_FIXED_COLD_WARM] PROGMEM = { 0,0, 255,0, 0,255, 128,128 };
 
-const uint8_t ledTable[] = {
+// New version of Gamma correction table, with adaptative resolution
-  0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+// from 11 bits (lower values) to 8 bits (upper values).
-  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+// We're using the fact that lower values are small and can fit within 8 bits
-  1,  2,  2,  2,  2,  2,  2,  2,  2,  3,  3,  3,  3,  3,  4,  4,
+// To save flash space, the array is only 8 bits uint
-  4,  4,  4,  5,  5,  5,  5,  6,  6,  6,  6,  7,  7,  7,  7,  8,
+const uint8_t _ledTable[] = {
-  8,  8,  9,  9,  9, 10, 10, 10, 11, 11, 12, 12, 12, 13, 13, 14,
+  // 11 bits resolution
- 14, 15, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 22,
+    0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  2,  2,  // 11 bits, 0..2047
- 22, 23, 23, 24, 25, 25, 26, 26, 27, 28, 28, 29, 30, 30, 31, 32,
+    2,  2,  2,  2,  3,  3,  3,  3,  4,  4,  4,  5,  5,  6,  6,  7,  // 11 bits, 0..2047
- 33, 33, 34, 35, 36, 36, 37, 38, 39, 40, 40, 41, 42, 43, 44, 45,
+    7,  8,  8,  9, 10, 10, 11, 12, 12, 13, 14, 15, 16, 17, 18, 19,  // 11 bits, 0..2047
- 46, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60,
+   20, 21, 22, 24, 25, 26, 28, 29, 30, 32, 33, 35, 37, 38, 40, 42,  // 11 bits, 0..2047
- 61, 62, 63, 64, 65, 67, 68, 69, 70, 71, 72, 73, 75, 76, 77, 78,
+  // 10 bits resolution
- 80, 81, 82, 83, 85, 86, 87, 89, 90, 91, 93, 94, 95, 97, 98, 99,
+   22, 23, 24, 25, 26, 27, 28, 30, 31, 32, 33, 34, 36, 37, 38, 39,  // 10 bits, 0..1023
-101,102,104,105,107,108,110,111,113,114,116,117,119,121,122,124,
+   41, 42, 44, 45, 47, 48, 50, 51, 53, 55, 56, 58, 60, 62, 64, 65,  // 10 bits, 0..1023
-125,127,129,130,132,134,135,137,139,141,142,144,146,148,150,151,
+   67, 69, 71, 73, 75, 78, 80, 82, 84, 86, 89, 91, 93, 96, 98,101,  // 10 bits, 0..1023
-153,155,157,159,161,163,165,166,168,170,172,174,176,178,180,182,
+  103,106,108,111,114,116,119,122,125,128,131,134,137,140,143,146,  // 10 bits, 0..1023
-184,186,189,191,193,195,197,199,201,204,206,208,210,212,215,217,
+  // 9 bits resolution
-219,221,224,226,228,231,233,235,238,240,243,245,248,250,253,255 };
+   75, 77, 78, 80, 82, 84, 85, 87, 89, 91, 93, 94, 96, 98,100,102,  //  9 bits, 0..511
+  104,106,108,110,112,115,117,119,121,123,125,128,130,132,135,137,  //  9 bits, 0..511
+  140,142,144,147,149,152,155,157,160,163,165,168,171,173,176,179,  //  9 bits, 0..511
+  182,185,188,191,194,197,200,203,206,209,212,215,219,222,225,229,  //  9 bits, 0..511
+  // 8 bits resolution
+  116,118,120,121,123,125,127,128,130,132,134,136,138,139,141,143,  //  8 bits, 0..255
+  145,147,149,151,153,155,157,159,161,163,165,168,170,172,174,176,  //  8 bits, 0..255
+  178,181,183,185,187,190,192,194,197,199,201,204,206,209,211,214,  //  8 bits, 0..255
+  216,219,221,224,226,229,232,234,237,240,242,245,248,250,253,255   //  8 bits, 0..255
+};
+
+// For reference, below are the computed gamma tables, via ledGamma()
+// for 8 bits output:
+//  0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+//  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+//  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,  2,  2,  2,  3,  3,  3,
+//  3,  3,  3,  3,  4,  4,  4,  4,  4,  4,  5,  5,  5,  5,  5,  6,
+//  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  9,  9,  9, 10, 10, 10,
+// 11, 11, 11, 12, 12, 12, 13, 13, 14, 14, 14, 15, 15, 16, 16, 17,
+// 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 23, 23, 24, 24, 25, 26,
+// 26, 27, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36, 37,
+// 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 47, 48, 49, 50, 51,
+// 52, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 64, 65, 66, 68, 69,
+// 70, 71, 72, 74, 75, 76, 78, 79, 80, 82, 83, 84, 86, 87, 88, 90,
+// 91, 93, 94, 96, 97, 99,100,102,103,105,106,108,110,111,113,115,
+//116,118,120,121,123,125,127,128,130,132,134,136,138,139,141,143,
+//145,147,149,151,153,155,157,159,161,163,165,168,170,172,174,176,
+//178,181,183,185,187,190,192,194,197,199,201,204,206,209,211,214,
+//216,219,221,224,226,229,232,234,237,240,242,245,248,250,253,255
+//
+// and for 10 bits output:
+//  0,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,  1,
+//  1,  1,  1,  1,  2,  2,  2,  2,  2,  2,  2,  3,  3,  3,  3,  4,
+//  4,  4,  4,  5,  5,  5,  6,  6,  6,  7,  7,  8,  8,  9,  9, 10,
+// 10, 11, 11, 12, 13, 13, 14, 15, 15, 16, 17, 18, 19, 19, 20, 21,
+// 22, 23, 24, 25, 26, 27, 28, 30, 31, 32, 33, 34, 36, 37, 38, 39,
+// 41, 42, 44, 45, 47, 48, 50, 51, 53, 55, 56, 58, 60, 62, 64, 65,
+// 67, 69, 71, 73, 75, 78, 80, 82, 84, 86, 89, 91, 93, 96, 98,101,
+//103,106,108,111,114,116,119,122,125,128,131,134,137,140,143,146,
+//151,155,157,161,165,169,171,175,179,183,187,189,193,197,201,205,
+//209,213,217,221,225,231,235,239,243,247,251,257,261,265,271,275,
+//281,285,289,295,299,305,311,315,321,327,331,337,343,347,353,359,
+//365,371,377,383,389,395,401,407,413,419,425,431,439,445,451,459,
+//467,475,483,487,495,503,511,515,523,531,539,547,555,559,567,575,
+//583,591,599,607,615,623,631,639,647,655,663,675,683,691,699,707,
+//715,727,735,743,751,763,771,779,791,799,807,819,827,839,847,859,
+//867,879,887,899,907,919,931,939,951,963,971,983,995,1003,1015,1023
+
 
 uint8_t light_entry_color[5];
 uint8_t light_current_color[5];
@@ -747,6 +794,38 @@ public:
 LightStateClass light_state = LightStateClass();
 LightControllerClass light_controller = LightControllerClass(light_state);
 
+/*********************************************************************************************\
+ * Gamma correction
+\*********************************************************************************************/
+// uint16_t ledGamma(uint8_t v, uint16_t max_range = 255) {
+//   uint16_t slot = 3 - (v / 64);  // 0..3
+//   uint16_t uncorrected_value = _ledTable[v];
+//   uint16_t range = (0x100 << slot) - 1;
+//   return changeUIntScale(uncorrected_value, 0, range, 0, max_range);
+// }
+// bits can be 8,9,10,11
+uint16_t ledGamma(uint8_t v, uint16_t bits_out = 8) {
+  uint16_t result;
+  // bits_resolution: the resolution of _ledTable[v], between 8 and 11
+  uint32_t bits_resolution = 11 - (v / 64);                     // 8..11
+  int32_t  bits_correction = bits_out - bits_resolution;      // -3..3
+  uint32_t uncorrected_value = _ledTable[v];        // 0..255
+  if (0 == bits_correction) {
+    // we already match the required resolution, no change
+    result = uncorrected_value;
+  } else if (bits_correction > 0) {
+    // the output resolution is higher than our value, we need to extrapolate
+    // we shift by bits_correction, and force last bits to 1
+    uint32_t bits_mask = (1 << bits_correction) - 1;  // 1, 3, 7
+    result = (uncorrected_value << bits_correction) | bits_mask;
+  } else {  // bits_correction < 0
+    // our resolution is too high, we need to remove bits
+    // we add 1, 3 or 7 to force rouding to the nearest high value
+    uint32_t bits_mask = (1 << -bits_correction) - 1;  // 1, 3, 7
+    result = ((uncorrected_value + bits_mask) >> -bits_correction);
+  }
+  return result;
+}
 
 #ifdef USE_ARILUX_RF
 /*********************************************************************************************\
@@ -1531,7 +1610,7 @@ void LightAnimate(void)
       for (uint8_t i = 0; i < light_subtype; i++) {
         light_last_color[i] = light_new_color[i];
         cur_col[i] = light_last_color[i]*Settings.rgbwwTable[i]/255;
-        cur_col[i] = (Settings.light_correction) ? ledTable[cur_col[i]] : cur_col[i];
+        cur_col[i] = (Settings.light_correction) ? ledGamma(cur_col[i]) : cur_col[i];
       }
 
       // color remapping

sonoff/xplg_ws2812.ino

@@ -99,11 +99,11 @@ void Ws2812StripShow(void)
   if (Settings.light_correction) {
     for (uint16_t i = 0; i < Settings.light_pixels; i++) {
       c = strip->GetPixelColor(i);
-      c.R = ledTable[c.R];
+      c.R = ledGamma(c.R);
-      c.G = ledTable[c.G];
+      c.G = ledGamma(c.G);
-      c.B = ledTable[c.B];
+      c.B = ledGamma(c.B);
 #if (USE_WS2812_CTYPE > NEO_3LED)
-      c.W = ledTable[c.W];
+      c.W = ledGamma(c.W);
 #endif
       strip->SetPixelColor(i, c);
     }