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fixed CIE brightness calculation for PWM outputs

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This commit is contained in:
Damian Schneider 2024-12-23 14:57:22 +01:00
parent 9dad436f72
commit 0ad65f4748
1 changed files with 8 additions and 12 deletions
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20
wled00/bus_manager.cpp
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@ -563,19 +563,15 @@ void BusPwm::show() {
const unsigned maxBri = (1<<_depth); // possible values: 16384 (14), 8192 (13), 4096 (12), 2048 (11), 1024 (10), 512 (9) and 256 (8)
[[maybe_unused]] const unsigned bitShift = dithering * 4; // if dithering, _depth is 12 bit but LEDC channel is set to 8 bit (using 4 fractional bits)
// use CIE brightness formula (cubic) to fit (or approximate linearity of) human eye perceived brightness
// the formula is based on 12 bit resolution as there is no need for greater precision
// use CIE brightness formula (linear + cubic) to approximate human eye perceived brightness
// see: https://en.wikipedia.org/wiki/Lightness
unsigned pwmBri = (unsigned)_bri * 100; // enlarge to use integer math for linear response
if (pwmBri < 2040) {
// linear response for values [0-20]
pwmBri = ((pwmBri << 12) + 115043) / 230087; //adding '0.5' before division for correct rounding
} else {
// cubic response for values [21-255]
pwmBri += 4080;
float temp = (float)pwmBri / 29580.0f;
temp = temp * temp * temp * (float)maxBri;
pwmBri = (unsigned)temp; // pwmBri is in range [0-maxBri]
unsigned pwmBri = _bri;
if (pwmBri < 21) { // linear response for values [0-20]
pwmBri = (pwmBri * maxBri + 2300 / 2) / 2300 ; // adding '0.5' before division for correct rounding, 2300 gives a good match to CIE curve
} else { // cubic response for values [21-255]
float temp = float(pwmBri + 41) / float(255 + 41); // 41 is to match offset & slope to linear part
temp = temp * temp * temp * (float)maxBri;
pwmBri = (unsigned)temp; // pwmBri is in range [0-maxBri] C
}
[[maybe_unused]] unsigned hPoint = 0; // phase shift (0 - maxBri)