Extract, test and slightly adjust the piecewise LUT for inverse gamma.

1 files changed, 76 insertions, 0 deletions

diff --git a/src/piecewise_lut.h b/src/piecewise_lut.h
new file mode 100644
index 00000000..ba8f5c13
--- /dev/null
+++ b/src/piecewise_lut.h
@@ -0,0 +1,76 @@
+/*
+    Copyright (C) 2013-2021 Carl Hetherington <cth@carlh.net>
+
+    This file is part of libdcp.
+
+    libdcp 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.
+
+    libdcp 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 libdcp.  If not, see <http://www.gnu.org/licenses/>.
+
+    In addition, as a special exception, the copyright holders give
+    permission to link the code of portions of this program with the
+    OpenSSL library under certain conditions as described in each
+    individual source file, and distribute linked combinations
+    including the two.
+
+    You must obey the GNU General Public License in all respects
+    for all of the code used other than OpenSSL.  If you modify
+    file(s) with this exception, you may extend this exception to your
+    version of the file(s), but you are not obligated to do so.  If you
+    do not wish to do so, delete this exception statement from your
+    version.  If you delete this exception statement from all source
+    files in the program, then also delete it here.
+*/
+
+
+#ifndef LIBDCP_PIECEWISE_LUT_H
+#define LIBDCP_PIECEWISE_LUT_H
+
+
+#include "transfer_function.h"
+#include <memory>
+#include <vector>
+
+
+namespace dcp {
+
+
+class PiecewiseLUT2
+{
+public:
+	PiecewiseLUT2(std::shared_ptr<const TransferFunction> fn, double boundary, int low_bits, int high_bits, bool inverse)
+		: _boundary(boundary)
+		, _low(fn->lut(0, boundary, low_bits, inverse))
+		, _high(fn->lut(boundary, 1, high_bits, inverse))
+		, _low_scale(static_cast<int>(std::pow(2.0f, low_bits)) - 1)
+		, _high_scale(static_cast<int>(std::pow(2.0f, high_bits)) - 1)
+	{
+
+	}
+
+	inline double lookup(double x) const {
+		return x < _boundary ?  _low[lrint((x / _boundary) * _low_scale)] : _high[lrint(((x - _boundary) / (1 - _boundary)) * _high_scale)];
+	}
+
+private:
+	double _boundary;
+	std::vector<double> _low;
+	std::vector<double> _high;
+	int _low_scale;
+	int _high_scale;
+};
+
+
+}
+
+#endif
+