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/*
Copyright (C) 2012-2014 Carl Hetherington <cth@carlh.net>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include "modified_gamma_transfer_function.h"
#include <cmath>
using std::pow;
using boost::shared_ptr;
using boost::dynamic_pointer_cast;
using namespace dcp;
ModifiedGammaTransferFunction::ModifiedGammaTransferFunction (double power, double threshold, double A, double B)
: _power (power)
, _threshold (threshold)
, _A (A)
, _B (B)
{
}
double *
ModifiedGammaTransferFunction::make_lut (int bit_depth, bool inverse) const
{
int const bit_length = int(std::pow(2.0f, bit_depth));
double* lut = new double[bit_length];
if (inverse) {
double const threshold = _threshold / _B;
for (int i = 0; i < bit_length; ++i) {
double const p = static_cast<double> (i) / (bit_length - 1);
if (p > threshold) {
lut[i] = (1 + _A) * pow (p, 1 / _power) - _A;
} else {
lut[i] = p * _B;
}
}
} else {
for (int i = 0; i < bit_length; ++i) {
double const p = static_cast<double> (i) / (bit_length - 1);
if (p > _threshold) {
lut[i] = pow ((p + _A) / (1 + _A), _power);
} else {
lut[i] = p / _B;
}
}
}
return lut;
}
bool
ModifiedGammaTransferFunction::about_equal (shared_ptr<const TransferFunction> other, double epsilon) const
{
shared_ptr<const ModifiedGammaTransferFunction> o = dynamic_pointer_cast<const ModifiedGammaTransferFunction> (other);
if (!o) {
return false;
}
return (
fabs (_power - o->_power) < epsilon &&
fabs (_threshold - o->_threshold) < epsilon &&
fabs (_A - o->_A) < epsilon &&
fabs (_B - o->_B) < epsilon
);
}
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