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16 Bit Gamma improvements (#645)
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* Gamma for 16bit Table Method
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@Makuna
Makuna authored Feb 10, 2023
1 parent fff81b9 commit d6ccd6d
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Showing 4 changed files with 89 additions and 24 deletions.
4 changes: 2 additions & 2 deletions examples/NeoPixelBusLg/NeoPixelBusLg.ino
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Expand Up @@ -22,11 +22,11 @@ RgbColor white(255, 255, 255);
// for your NeoPixels
NeoPixelBusLg<NeoRgbFeature, NeoWs2812xMethod> strip(PixelCount, PixelPin);

// If speed is an issue and memory is not, then you can use the gama table variant
// If speed is an issue and memory is not, then you can use the gamma table variant
// which is much faster but uses 256 bytes of RAM
// NeoPixelBusLg<NeoRgbFeature, NeoWs2812xMethod, NeoGammaTableMethod> strip(PixelCount, PixelPin);

// If you want to turn gama correction off, then you can use the null gama method
// If you want to turn gamma correction off, then you can use the null gamma method
// NeoPixelBusLg<NeoRgbFeature, NeoWs2812xMethod, NeoGammaNullMethod> strip(PixelCount, PixelPin);

void setup()
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2 changes: 1 addition & 1 deletion src/NeoPixelBusLg.h
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Expand Up @@ -74,7 +74,7 @@ template<typename T_COLOR_FEATURE, typename T_METHOD, typename T_GAMMA = NeoGamm
{
// does NOT affect current pixel data as there is no safe way
// to reconstruct the original color values after being
// modified with both luminance and gama without storing them
// modified with both luminance and gamma without storing them
_luminance = luminance;
}

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32 changes: 16 additions & 16 deletions src/internal/NeoGamma.cpp
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Expand Up @@ -28,20 +28,20 @@ License along with NeoPixel. If not, see
#include "NeoPixelBus.h"

const uint8_t NeoGammaTableMethod::_table[] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2,
3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6,
6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 11, 11, 11,
12, 12, 13, 13, 14, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19,
19, 20, 20, 21, 22, 22, 23, 23, 24, 25, 25, 26, 26, 27, 28, 28,
29, 30, 30, 31, 32, 33, 33, 34, 35, 35, 36, 37, 38, 39, 39, 40,
41, 42, 43, 43, 44, 45, 46, 47, 48, 49, 50, 50, 51, 52, 53, 54,
55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 71,
72, 73, 74, 75, 76, 77, 78, 80, 81, 82, 83, 84, 86, 87, 88, 89,
91, 92, 93, 94, 96, 97, 98, 100, 101, 102, 104, 105, 106, 108, 109, 110,
112, 113, 115, 116, 118, 119, 121, 122, 123, 125, 126, 128, 130, 131, 133, 134,
136, 137, 139, 140, 142, 144, 145, 147, 149, 150, 152, 154, 155, 157, 159, 160,
162, 164, 166, 167, 169, 171, 173, 175, 176, 178, 180, 182, 184, 186, 187, 189,
191, 193, 195, 197, 199, 201, 203, 205, 207, 209, 211, 213, 215, 217, 219, 221,
223, 225, 227, 229, 231, 233, 235, 238, 240, 242, 244, 246, 248, 251, 253, 255
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 16
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, // 32
3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, // 48
6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 11, 11, 11, // 64
12, 12, 13, 13, 14, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, // 80
19, 20, 20, 21, 22, 22, 23, 23, 24, 25, 25, 26, 26, 27, 28, 28, // 96
29, 30, 30, 31, 32, 33, 33, 34, 35, 35, 36, 37, 38, 39, 39, 40, // 112
41, 42, 43, 43, 44, 45, 46, 47, 48, 49, 50, 50, 51, 52, 53, 54, // 128
55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, // 144
71, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 84, 85, 87, 88, 89, // 160
90, 91, 93, 94, 95, 97, 98, 99, 101, 102, 103, 105, 106, 107, 109, 110, // 176
111, 113, 114, 116, 117, 119, 120, 122, 123, 125, 126, 128, 129, 131, 132, 134, // 192
135, 137, 138, 140, 142, 143, 145, 146, 148, 150, 151, 153, 155, 156, 158, 160, // 208
162, 163, 165, 167, 168, 170, 172, 174, 176, 177, 179, 181, 183, 185, 187, 189, // 224
190, 192, 194, 196, 198, 200, 202, 203, 206, 207, 210, 212, 214, 216, 218, 220, // 240
222, 224, 226, 228, 230, 232, 234, 237, 239, 241, 243, 245, 247, 250, 251, 255 // 256
};
75 changes: 70 additions & 5 deletions src/internal/NeoGamma.h
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Expand Up @@ -40,6 +40,12 @@ class NeoGammaEquationMethod
}
};

struct NeoGamma16LowHint
{
uint8_t pos;
uint8_t count;
};

// NeoGammaTableMethod uses 256 bytes of memory, but is significantly faster
class NeoGammaTableMethod
{
Expand All @@ -48,16 +54,75 @@ class NeoGammaTableMethod
{
return _table[value];
}
/*

static uint16_t Correct(uint16_t value)
{
// NOTE: 16 bit color elements not supported with NeoGammaTableMethod, use NeoGammaEquationMethod
return 0;
{
// since a single monolithic table would be an unreasonable memory usage
// this will use a hybrid of two tables, the base 255 table for the hibyte
// and a smaller table with hints on how to use the table for certain values
// and the left over values some simple calculations to approximate the final
// 16 bit value as compared to the equation
static const NeoGamma16LowHint _hints[] = {
{0,16}, {1,16}, {2,16}, {3,16}, {4,16}, {5,16}, {6,16}, {7,16}, {8,16}, {9,16}, {10,16}, {11,16}, {12,16}, {13,16}, {14,16}, {15,16},
{0,10}, {1,10}, {2,10}, {3,10}, {4,10}, {5,10}, {6,10}, {7,10}, {8,10}, {9,10}, {0,6}, {1,6}, {2,6}, {3,6}, {4,6}, {5,6},
{0,6}, {1,6}, {2,6}, {3,6}, {4,6}, {5,6}, {0,4}, {1,4}, {2,4}, {3,4}, {0,4}, {1,4}, {2,4}, {3,4}, {0,3}, {1,3},
{2,3}, {0,4}, {1,4}, {2,4}, {3,4}, {0,3}, {1,3}, {2,3}, {0,3}, {1,3}, {2,3}, {0,2}, {1,2}, {0,3}, {1,3}, {2,3},
{0,2}, {1,2}, {0,2}, {1,2}, {0,3}, {1,3}, {2,3}, {0,2}, {1,2}
};

uint8_t hi = (value >> 8);
uint16_t lo = (value & 0x00ff);
uint8_t hiResult = _table[hi];
uint16_t lowResult = 0;

if (hi < countof(_hints))
{
// use _hints table to calculate a reasonable lowbyte
lowResult = (lo + _hints[hi].pos * 256) / _hints[hi].count;
}
else if (hi == 255)
{
// last entry is always linear
lowResult = lo;
}
else
{
// check the _table for duplicate or jumps to adjust the range of lowbyte
if (hiResult == _table[hi - 1])
{
// this result is an upper duplicate
lowResult = (lo >> 1) | 0x80; // lo / 2 + 128
}
else
{
uint8_t delta = _table[hi + 1] - hiResult;

if (delta == 0)
{
// this result is a lower duplicate
lowResult = (lo >> 1); // lo / 2
}
else if (delta == 1)
{
// this result is incremental and thus linear
lowResult = lo;
}
else
{
// this result jumps by more than one, so need to spread across
lowResult = delta * lo;
}
}

}

return (static_cast<uint16_t>(hiResult) << 8) + lowResult;
}
*/


private:
static const uint8_t _table[256];

};

// no gamma correction at all
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