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jlechner |
/* LinearRGBConverter.java -- conversion to a linear RGB color space
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Copyright (C) 2004 Free Software Foundation
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.java.awt.color;
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/**
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* LinearRGBConverter - conversion routines for a linear sRGB colorspace
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* sRGB is a standard for RGB colorspaces, adopted by the w3c.
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*
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* The specification is available at:
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* http://www.w3.org/Graphics/Color/sRGB.html
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*
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* @author Sven de Marothy
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*/
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public class LinearRGBConverter implements ColorSpaceConverter
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{
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/**
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* linear RGB --> sRGB
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* Use the inverse gamma curve
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*/
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public float[] toRGB(float[] in)
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{
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float[] out = new float[3];
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for (int i = 0; i < 3; i++)
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{
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float n = in[i];
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if (n < 0)
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n = 0f;
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if (n > 1)
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n = 1f;
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if (n <= 0.00304f)
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out[i] = in[0] * 12.92f;
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else
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out[i] = 1.055f * ((float) Math.exp((1 / 2.4) * Math.log(n)))
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- 0.055f;
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}
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return out;
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}
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/**
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* sRGB --> linear RGB
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* Use the gamma curve (gamma=2.4 in sRGB)
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*/
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public float[] fromRGB(float[] in)
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{
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float[] out = new float[3];
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// Convert non-linear RGB coordinates to linear ones,
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// numbers from the w3 spec.
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for (int i = 0; i < 3; i++)
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{
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float n = in[i];
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if (n < 0)
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n = 0f;
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if (n > 1)
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n = 1f;
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if (n <= 0.03928f)
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out[i] = (float) (n / 12.92);
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else
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out[i] = (float) (Math.exp(2.4 * Math.log((n + 0.055) / 1.055)));
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}
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return out;
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}
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/**
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* Linear RGB --> CIE XYZ (D50 relative)
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* This is a simple matrix transform, the matrix (relative D65)
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* is given in the sRGB spec. This has been combined with a
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* linear Bradford transform for the D65-->D50 mapping, resulting
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* in a single matrix which does the whole thing.
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*
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*/
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public float[] fromCIEXYZ(float[] in)
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{
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/*
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* Note: The numbers which were used to calculate this only had four
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* digits of accuracy. So don't be fooled by the number of digits here.
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* If someone has more accurate source, feel free to update this.
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*/
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float[] out = new float[3];
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out[0] = (float) (3.13383065124221 * in[0] - 1.61711949411313 * in[1]
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- 0.49071914111101 * in[2]);
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out[1] = (float) (-0.97847026691142 * in[0] + 1.91597856031996 * in[1]
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+ 0.03340430640699 * in[2]);
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out[2] = (float) (0.07203679486279 * in[0] - 0.22903073553113 * in[1]
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+ 1.40557835776234 * in[2]);
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if (out[0] < 0)
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out[0] = 0f;
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if (out[1] < 0)
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out[1] = 0f;
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if (out[2] < 0)
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out[2] = 0f;
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if (out[0] > 1.0f)
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out[0] = 1.0f;
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if (out[1] > 1.0f)
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out[1] = 1.0f;
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if (out[2] > 1.0f)
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out[2] = 1.0f;
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return out;
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}
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/**
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* Linear RGB --> CIE XYZ (D50 relative)
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* Uses the inverse of the above matrix.
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*/
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public float[] toCIEXYZ(float[] in)
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{
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float[] out = new float[3];
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out[0] = (float) (0.43606375022190 * in[0] + 0.38514960146481 * in[1]
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+ 0.14308641888799 * in[2]);
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out[1] = (float) (0.22245089403542 * in[0] + 0.71692584775182 * in[1]
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+ 0.06062451125578 * in[2]);
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out[2] = (float) (0.01389851860679 * in[0] + 0.09707969011198 * in[1]
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+ 0.71399604572506 * in[2]);
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return out;
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}
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}
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