Hub75: Replace and document gamma correction table.

pimoroni · Feb 6, 2025 · 1c36b05 · 1c36b05
1 parent 768251f
commit 1c36b05
Showing 1 changed file with 31 additions and 18 deletions.
diff --git a/drivers/hub75/hub75.hpp b/drivers/hub75/hub75.hpp
@@ -17,25 +17,38 @@ const uint ROWSEL_BASE_PIN = 6;
 const uint ROWSEL_N_PINS = 5;
 const uint BIT_DEPTH = 10;
 
-// This gamma table is used to correct our 8-bit (0-255) colours up to 11-bit,
-// allowing us to gamma correct without losing dynamic range.
+/*
+10-bit gamma table, allowing us to gamma correct our 8-bit colour values up
+to 10-bit without losing dynamic range.
+
+Calculated with the following Python code:
+
+gamma_lut = [int(round(1024 * (x / (256 - 1)) ** 2.2)) for x in range(256)]
+
+Post-processed to enforce a minimum difference of 1 between adjacent values,
+and no leading zeros:
+
+for i in range(1, len(gamma_lut)):
+	if gamma_lut[i] <= gamma_lut[i - 1]:
+		gamma_lut[i] = gamma_lut[i - 1] + 1
+*/
 constexpr uint16_t GAMMA_10BIT[256] = {
-    0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8,
-    8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16,
-    16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 24, 25,
-    26, 27, 29, 30, 31, 33, 34, 35, 37, 38, 40, 41, 43, 44, 46, 47,
-    49, 51, 53, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78,
-    80, 82, 85, 87, 89, 92, 94, 96, 99, 101, 104, 106, 109, 112, 114, 117,
-    120, 122, 125, 128, 131, 134, 137, 140, 143, 146, 149, 152, 155, 158, 161, 164,
-    168, 171, 174, 178, 181, 185, 188, 192, 195, 199, 202, 206, 210, 214, 217, 221,
-    225, 229, 233, 237, 241, 245, 249, 253, 257, 261, 265, 270, 274, 278, 283, 287,
-    291, 296, 300, 305, 309, 314, 319, 323, 328, 333, 338, 343, 347, 352, 357, 362,
-    367, 372, 378, 383, 388, 393, 398, 404, 409, 414, 420, 425, 431, 436, 442, 447,
-    453, 459, 464, 470, 476, 482, 488, 494, 499, 505, 511, 518, 524, 530, 536, 542,
-    548, 555, 561, 568, 574, 580, 587, 593, 600, 607, 613, 620, 627, 633, 640, 647,
-    654, 661, 668, 675, 682, 689, 696, 703, 711, 718, 725, 733, 740, 747, 755, 762,
-    770, 777, 785, 793, 800, 808, 816, 824, 832, 839, 847, 855, 863, 872, 880, 888,
-    896, 904, 912, 921, 929, 938, 946, 954, 963, 972, 980, 989, 997, 1006, 1015, 1023
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+    16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
+    32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
+    48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
+    64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
+    80, 82, 84, 87, 89, 91, 94, 96, 98, 101, 103, 106, 109, 111, 114, 117,
+    119, 122, 125, 128, 130, 133, 136, 139, 142, 145, 148, 151, 155, 158, 161, 164,
+    167, 171, 174, 177, 181, 184, 188, 191, 195, 198, 202, 206, 209, 213, 217, 221,
+    225, 228, 232, 236, 240, 244, 248, 252, 257, 261, 265, 269, 274, 278, 282, 287,
+    291, 295, 300, 304, 309, 314, 318, 323, 328, 333, 337, 342, 347, 352, 357, 362,
+    367, 372, 377, 382, 387, 393, 398, 403, 408, 414, 419, 425, 430, 436, 441, 447,
+    452, 458, 464, 470, 475, 481, 487, 493, 499, 505, 511, 517, 523, 529, 535, 542,
+    548, 554, 561, 567, 573, 580, 586, 593, 599, 606, 613, 619, 626, 633, 640, 647,
+    653, 660, 667, 674, 681, 689, 696, 703, 710, 717, 725, 732, 739, 747, 754, 762,
+    769, 777, 784, 792, 800, 807, 815, 823, 831, 839, 847, 855, 863, 871, 879, 887,
+    895, 903, 912, 920, 928, 937, 945, 954, 962, 971, 979, 988, 997, 1005, 1014, 1023
 };