1 /* SrgbConverter.java -- sRGB conversion class 2 Copyright (C) 2004 Free Software Foundation 3 4 This file is part of GNU Classpath. 5 6 GNU Classpath is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 2, or (at your option) 9 any later version. 10 11 GNU Classpath is distributed in the hope that it will be useful, but 12 WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GNU Classpath; see the file COPYING. If not, write to the 18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19 02110-1301 USA. 20 21 Linking this library statically or dynamically with other modules is 22 making a combined work based on this library. Thus, the terms and 23 conditions of the GNU General Public License cover the whole 24 combination. 25 26 As a special exception, the copyright holders of this library give you 27 permission to link this library with independent modules to produce an 28 executable, regardless of the license terms of these independent 29 modules, and to copy and distribute the resulting executable under 30 terms of your choice, provided that you also meet, for each linked 31 independent module, the terms and conditions of the license of that 32 module. An independent module is a module which is not derived from 33 or based on this library. If you modify this library, you may extend 34 this exception to your version of the library, but you are not 35 obligated to do so. If you do not wish to do so, delete this 36 exception statement from your version. */ 37 38 package gnu.java.awt.color; 39 40 41 /** 42 * SrgbConverter - conversion routines for the sRGB colorspace 43 * sRGB is a standard for RGB colorspaces, adopted by the w3c. 44 * 45 * The specification is available at: 46 * http://www.w3.org/Graphics/Color/sRGB.html 47 * 48 * @author Sven de Marothy 49 */ 50 /** 51 * 52 * Note the matrix numbers used here are NOT identical to those in the 53 * w3 spec, as those numbers are CIE XYZ relative a D65 white point. 54 * The CIE XYZ we use is relative a D50 white point, so therefore a 55 * linear Bradford transform matrix for D65->D50 mapping has been applied. 56 * (The ICC documents describe this transform) 57 * 58 * Linearized Bradford transform: 59 * 0.8951 0.2664 -0.1614 60 * -0.7502 1.7135 0.0367 61 * 0.0389 -0.0685 1.0296 62 * 63 * Inverse: 64 * 0.9870 -0.1471 0.1600 65 * 0.4323 0.5184 0.0493 66 * -0.00853 0.0400 0.9685 67 */ 68 public class SrgbConverter implements ColorSpaceConverter 69 { fromCIEXYZ(float[] in)70 public float[] fromCIEXYZ(float[] in) 71 { 72 return XYZtoRGB(in); 73 } 74 toCIEXYZ(float[] in)75 public float[] toCIEXYZ(float[] in) 76 { 77 return RGBtoXYZ(in); 78 } 79 toRGB(float[] in)80 public float[] toRGB(float[] in) 81 { 82 float[] out = new float[3]; 83 System.arraycopy(in, 0, out, 0, 3); 84 return out; 85 } 86 fromRGB(float[] in)87 public float[] fromRGB(float[] in) 88 { 89 float[] out = new float[3]; 90 System.arraycopy(in, 0, out, 0, 3); 91 return out; 92 } 93 94 /** 95 * CIE XYZ (D50 relative) --> sRGB 96 * 97 * Static as it's used by other ColorSpaceConverters to 98 * convert to sRGB if the color space is defined in XYZ. 99 */ XYZtoRGB(float[] in)100 public static float[] XYZtoRGB(float[] in) 101 { 102 float[] temp = new float[3]; 103 temp[0] = 3.1338f * in[0] - 1.6171f * in[1] - 0.4907f * in[2]; 104 temp[1] = -0.9785f * in[0] + 1.9160f * in[1] + 0.0334f * in[2]; 105 temp[2] = 0.0720f * in[0] - 0.2290f * in[1] + 1.4056f * in[2]; 106 107 float[] out = new float[3]; 108 for (int i = 0; i < 3; i++) 109 { 110 if (temp[i] < 0) 111 temp[i] = 0.0f; 112 if (temp[i] > 1) 113 temp[i] = 1.0f; 114 if (temp[i] <= 0.00304f) 115 out[i] = temp[i] * 12.92f; 116 else 117 out[i] = 1.055f * ((float) Math.exp((1 / 2.4) * Math.log(temp[i]))) 118 - 0.055f; 119 } 120 return out; 121 } 122 123 /** 124 * sRGB --> CIE XYZ (D50 relative) 125 * 126 * Static as it's used by other ColorSpaceConverters to 127 * convert to XYZ if the color space is defined in RGB. 128 */ RGBtoXYZ(float[] in)129 public static float[] RGBtoXYZ(float[] in) 130 { 131 float[] temp = new float[3]; 132 float[] out = new float[3]; 133 for (int i = 0; i < 3; i++) 134 if (in[i] <= 0.03928f) 135 temp[i] = in[i] / 12.92f; 136 else 137 temp[i] = (float) Math.exp(2.4 * Math.log((in[i] + 0.055) / 1.055)); 138 139 /* 140 * Note: The numbers which were used to calculate this only had four 141 * digits of accuracy. So don't be fooled by the number of digits here. 142 * If someone has more accurate source, feel free to update this. 143 */ 144 out[0] = (float) (0.436063750222 * temp[0] + 0.385149601465 * temp[1] 145 + 0.143086418888 * temp[2]); 146 out[1] = (float) (0.222450894035 * temp[0] + 0.71692584775 * temp[1] 147 + 0.060624511256 * temp[2]); 148 out[2] = (float) (0.0138985186 * temp[0] + 0.097079690112 * temp[1] 149 + 0.713996045725 * temp[2]); 150 return out; 151 } 152 } 153