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/**
* crt-calibrator – Calibration utility for CRT monitors
* Copyright © 2014 Mattias Andrée (maandree@member.fsf.org)
*
* 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 3 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, see <http://www.gnu.org/licenses/>.
*/
#include "gamma.h"
#include <math.h>
/**
* Analyse a gamma ramp
*
* @param stops The number of stops in the gamma ramp
* @param ramp The gamma ramp
* @param gamma Output parameter for the gamma
* @param contrast Output parameter for the contrast
* @param brightness Output parameter for the brightness
*/
void gamma_analyse(size_t stops, const uint16_t* restrict ramp, double* restrict gamma,
double* restrict contrast, double* restrict brightness)
{
double min, middle, max;
*brightness = min = (double)(ramp[0]) / (double)0xFFFF;
*contrast = max = (double)(ramp[stops - 1]) / (double)0xFFFF;
middle = (double)(ramp[stops / 2]) / (double)0xFFFF;
middle = (middle - min) / (max - min);
*gamma = log(2.0) / log(middle);
}
/**
* Generate a gamma ramp
*
* @param stops The number of stops in the gamma ramp
* @param ramp Memory area to where to write the gamma ramp
* @param gamma The gamma
* @param contrast The contrast
* @param brightness The brightness
*/
void gamma_generate(size_t stops, uint16_t* restrict ramp, double gamma,
double contrast, double brightness)
{
double diff = contrast - brightness;
double gamma_ = 1.0 / gamma;
size_t i;
int32_t y;
double y_;
for (i = 0; i < stops; i++)
{
y_ = (double)i / (double)stops;
y_ = pow(y_, gamma_) * diff + brightness;
y = (int32_t)(y * 0xFFFF);
if (y < 0x0000) y = 0x0000;
if (y > 0xFFFF) y = 0xFFFF;
ramp[i] = y;
}
}
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