001/* JPEGQTable.java -- 002 Copyright (C) 2006 Free Software Foundation, Inc. 003 004 This file is part of GNU Classpath. 005 006 GNU Classpath is free software; you can redistribute it and/or modify 007 it under the terms of the GNU General Public License as published by 008 the Free Software Foundation; either version 2, or (at your option) 009 any later version. 010 011 GNU Classpath is distributed in the hope that it will be useful, but 012 WITHOUT ANY WARRANTY; without even the implied warranty of 013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014 General Public License for more details. 015 016 You should have received a copy of the GNU General Public License 017 along with GNU Classpath; see the file COPYING. If not, write to the 018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 019 02110-1301 USA. 020 021 Linking this library statically or dynamically with other modules is 022 making a combined work based on this library. Thus, the terms and 023 conditions of the GNU General Public License cover the whole 024 combination. 025 026 As a special exception, the copyright holders of this library give you 027 permission to link this library with independent modules to produce an 028 executable, regardless of the license terms of these independent 029 modules, and to copy and distribute the resulting executable under 030 terms of your choice, provided that you also meet, for each linked 031 independent module, the terms and conditions of the license of that 032 module. An independent module is a module which is not derived from 033 or based on this library. If you modify this library, you may extend 034 this exception to your version of the library, but you are not 035 obligated to do so. If you do not wish to do so, delete this 036 exception statement from your version. */ 037 038 039package javax.imageio.plugins.jpeg; 040 041import gnu.java.lang.CPStringBuilder; 042 043/** 044 * The JPEGQTable class represents a quantization table that can be 045 * used to encode or decode a JPEG stream. The standard JPEG 046 * luminance and chrominance quantization tables are provided as 047 * static fields. Table entries are stored in natural order, not 048 * zig-zag order. 049 */ 050public class JPEGQTable 051{ 052 /** 053 * The table entries, stored in natural order. 054 */ 055 private int[] table; 056 057 /** 058 * The standard JPEG luminance quantization table. Values are 059 * stored in natural order. 060 */ 061 public static final JPEGQTable K1Luminance = new JPEGQTable(new int[] 062 { 063 16, 11, 10, 16, 24, 40, 51, 61, 064 12, 12, 14, 19, 26, 58, 60, 55, 065 14, 13, 16, 24, 40, 57, 69, 56, 066 14, 17, 22, 29, 51, 87, 80, 62, 067 18, 22, 37, 56, 68, 109, 103, 77, 068 24, 35, 55, 64, 81, 104, 113, 92, 069 49, 64, 78, 87, 103, 121, 120, 101, 070 72, 92, 95, 98, 112, 100, 103, 99 071 }, false); 072 073 /** 074 * The standard JPEG luminance quantization table, scaled by 075 * one-half. Values are stored in natural order. 076 */ 077 public static final JPEGQTable K1Div2Luminance = 078 K1Luminance.getScaledInstance(0.5f, true); 079 080 /** 081 * The standard JPEG chrominance quantization table. Values are 082 * stored in natural order. 083 */ 084 public static final JPEGQTable K2Chrominance = new JPEGQTable(new int[] 085 { 086 17, 18, 24, 47, 99, 99, 99, 99, 087 18, 21, 26, 66, 99, 99, 99, 99, 088 24, 26, 56, 99, 99, 99, 99, 99, 089 47, 66, 99, 99, 99, 99, 99, 99, 090 99, 99, 99, 99, 99, 99, 99, 99, 091 99, 99, 99, 99, 99, 99, 99, 99, 092 99, 99, 99, 99, 99, 99, 99, 99, 093 99, 99, 99, 99, 99, 99, 99, 99 094 }, false); 095 096 /** 097 * The standard JPEG chrominance quantization table, scaled by 098 * one-half. Values are stored in natural order. 099 */ 100 public static final JPEGQTable K2Div2Chrominance = 101 K2Chrominance.getScaledInstance(0.5f, true); 102 103 /** 104 * Construct a new JPEG quantization table. A copy is created of 105 * the table argument. 106 * 107 * @param table the 64-element value table, stored in natural order 108 * 109 * @throws IllegalArgumentException if the table is null or if 110 * table's length is not equal to 64. 111 */ 112 public JPEGQTable(int[] table) 113 { 114 this(checkTable(table), true); 115 } 116 117 /** 118 * Private constructor that avoids unnecessary copying and argument 119 * checking. 120 * 121 * @param table the 64-element value table, stored in natural order 122 * @param copy true if a copy should be created of the given table 123 */ 124 private JPEGQTable(int[] table, boolean copy) 125 { 126 this.table = copy ? (int[]) table.clone() : table; 127 } 128 129 private static int[] checkTable(int[] table) 130 { 131 if (table == null || table.length != 64) 132 throw new IllegalArgumentException("invalid JPEG quantization table"); 133 134 return table; 135 } 136 137 /** 138 * Retrieve a copy of the quantization values for this table. 139 * 140 * @return a copy of the quantization value array 141 */ 142 public int[] getTable() 143 { 144 return (int[]) table.clone(); 145 } 146 147 /** 148 * Retrieve a copy of this JPEG quantization table with every value 149 * scaled by the given scale factor, and clamped from 1 to 255 150 * baseline or from 1 to 32767 otherwise. 151 * 152 * @param scaleFactor the factor by which to scale this table 153 * @param forceBaseline clamp scaled values to a maximum of 255 if 154 * true, 32767 if false 155 * 156 * @return a new scaled JPEG quantization table 157 */ 158 public JPEGQTable getScaledInstance(float scaleFactor, 159 boolean forceBaseline) 160 { 161 int[] scaledTable = getTable(); 162 int max = forceBaseline ? 255 : 32767; 163 164 for (int i = 0; i < scaledTable.length; i++) 165 { 166 scaledTable[i] = Math.round (scaleFactor * (float) scaledTable[i]); 167 if (scaledTable[i] < 1) 168 scaledTable[i] = 1; 169 else if (scaledTable[i] > max) 170 scaledTable[i] = max; 171 } 172 173 // Do not copy scaledTable. It is already a copy because we used 174 // getTable to retrieve it. 175 return new JPEGQTable(scaledTable, false); 176 } 177 178 /** 179 * Create a string representing this JPEG quantization table. 180 */ 181 public String toString() 182 { 183 CPStringBuilder buffer = new CPStringBuilder(); 184 185 buffer.append("JPEGQTable:\n"); 186 for (int i = 0; i < 8; i++) 187 { 188 buffer.append(" "); 189 for (int j = 0; j < 8; j++) 190 { 191 buffer.append(table[i * 8 + j] + " "); 192 } 193 buffer.append("\n"); 194 } 195 196 return buffer.toString(); 197 } 198}