001/**
002 *
003 * Copyright (c) 2014, the Railo Company Ltd. All rights reserved.
004 *
005 * This library is free software; you can redistribute it and/or
006 * modify it under the terms of the GNU Lesser General Public
007 * License as published by the Free Software Foundation; either 
008 * version 2.1 of the License, or (at your option) any later version.
009 * 
010 * This library is distributed in the hope that it will be useful,
011 * but WITHOUT ANY WARRANTY; without even the implied warranty of
012 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013 * Lesser General Public License for more details.
014 * 
015 * You should have received a copy of the GNU Lesser General Public 
016 * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
017 * 
018 **/
019/*
020*
021
022Licensed under the Apache License, Version 2.0 (the "License");
023you may not use this file except in compliance with the License.
024You may obtain a copy of the License at
025
026   http://www.apache.org/licenses/LICENSE-2.0
027
028Unless required by applicable law or agreed to in writing, software
029distributed under the License is distributed on an "AS IS" BASIS,
030WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
031See the License for the specific language governing permissions and
032limitations under the License.
033*/
034
035package lucee.runtime.img.filter;
036/**
037 * A class for calulating the colors of the spectrum.
038 */
039public class Spectrum {
040
041        private static int adjust(float color, float factor, float gamma) {
042                if (color == 0.0)
043                        return 0;
044                return (int)Math.round(255 * Math.pow(color * factor, gamma));
045        }
046        
047        /**
048     * Convert a wavelength to an RGB value.
049         * @param wavelength wavelength in nanometres
050     * @return the RGB value
051         */
052        public static int wavelengthToRGB(float wavelength) {
053                float gamma = 0.80f;
054                float r, g, b, factor;
055
056                int w = (int)wavelength;
057                if (w < 380) {
058                        r = 0.0f;
059                        g = 0.0f;
060                        b = 0.0f;
061                } else if (w < 440) {
062                        r = -(wavelength - 440) / (440 - 380);
063                        g = 0.0f;
064                        b = 1.0f;
065                } else if (w < 490) {
066                        r = 0.0f;
067                        g = (wavelength - 440) / (490 - 440);
068                        b = 1.0f;
069                } else if (w < 510) {
070                        r = 0.0f;
071                        g = 1.0f;
072                        b = -(wavelength - 510) / (510 - 490);
073                } else if (w < 580) {
074                        r = (wavelength - 510) / (580 - 510);
075                        g = 1.0f;
076                        b = 0.0f;
077                } else if (w < 645) {
078                        r = 1.0f;
079                        g = -(wavelength - 645) / (645 - 580);
080                        b = 0.0f;
081                } else if (w <= 780) {
082                        r = 1.0f;
083                        g = 0.0f;
084                        b = 0.0f;
085                } else {
086                        r = 0.0f;
087                        g = 0.0f;
088                        b = 0.0f;
089                }
090
091                // Let the intensity fall off near the vision limits
092                if (380 <= w && w <= 419)
093                        factor = 0.3f + 0.7f*(wavelength - 380) / (420 - 380);
094                else if (420 <= w && w <= 700)
095                        factor = 1.0f;
096                else if (701 <= w && w <= 780)
097                        factor = 0.3f + 0.7f*(780 - wavelength) / (780 - 700);
098                else
099                        factor = 0.0f;
100
101                int ir = adjust(r, factor, gamma);
102                int ig = adjust(g, factor, gamma);
103                int ib = adjust(b, factor, gamma);
104
105                return 0xff000000 | (ir << 16) | (ig << 8) | ib;
106        }
107
108}