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/**
*
* This file is part of Tulip (www.tulip-software.org)
*
* Authors: David Auber and the Tulip development Team
* from LaBRI, University of Bordeaux
*
* Tulip is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License
* as published by the Free Software Foundation, either version 3
* of the License, or (at your option) any later version.
*
* Tulip 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.
*
*/
// This implementation of HSI Color Space is from the following paper : "Issues in Visualizing Large Databases"
// D. A. Keim, H.-P. Kriegel
#include "HSIColorSpace.h"
#include <cmath>
using namespace std;
namespace pocore {
/***************************** Constructor **********************************/
HSI::HSI(double h, double s, double i): hue( h<6 ? h : h-6 ), saturation(s), intensity(i) {}
/************************** Conversion from RGB to HSI ***********************/
HSI::HSI(const RGBA& c) {
double red = c[0], green = c[1], blue = c[2];
double mid = (red + green + blue) / 3.0;
double mr = red - mid;
double mg = green - mid;
double mb = blue - mid;
double cos_hue = (2.0 * mr - mg - mb) / sqrt((mr*mr + mg*mg + mb*mb) * 6.0);
intensity = mid + sqrt (2.0 * (mr*mr + mg*mg + mb*mb) / 3.0);
saturation = 2.0 * (intensity - mid) / intensity;
hue = acos( cos_hue ) * 3.0 / M_PI;
if (blue > green)
hue = 6.0 - hue;
}
/************************** Conversion from HSI to RGB ***********************/
RGBA HSI::getRGBA() const {
RGBA ret;
if (saturation == 0.0) {
ret[0] = (unsigned char) (intensity * 255);
ret[1] = (unsigned char) (intensity * 255);
ret[2] = (unsigned char) (intensity * 255);
ret[3] = 255;
}
else {
ret[0] = (unsigned char) (value(hue + 0.0) * 255); // 0 Grad = 0 pi
ret[1] = (unsigned char) (value(hue + 4.0) * 255); // 240 Grad = 4/3 pi
ret[2] = (unsigned char) (value(hue + 2.0) * 255); // 120 Grad = 2/3 pi
ret[3] = 255;
}
return ret;
}
double HSI::value(double hue_phase) const {
double pure = 0.5 * (1 + cos(hue_phase * M_PI / 3.0));
return (intensity * (1.0 - saturation * (1.0 - pure)));
}
/************************* Generation of HSIColorScales ************************/
HSIColorScale :: HSIColorScale( const HSI& from, const HSI& to )
: foot(from)
, hue_range(to.hue - from.hue)
, sat_range(to.saturation - from.saturation)
, int_range(to.intensity - from.intensity) {
if( hue_range < 0.0 )
hue_range += 6.0;
}
HSI HSIColorScale::operator[](double f) const {
return HSI(hue_range * f + foot.hue,
sat_range * f + foot.saturation,
int_range * f + foot.intensity);
}
}
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