awt/javax/imageio/plugins/jpeg/JPEGQTable.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
/**
 * @author Rustem V. Rafikov
 * @version $Revision: 1.3 $
 */
package javax.imageio.plugins.jpeg;

/**
 * The JPEGQTable class represents a single JPEG quantization table 
 * and provides for the standard tables taken from the JPEG specification.
 */
public class JPEGQTable {

    /** The Constant SIZE. */
    private final static int SIZE = 64;
    
    /** The Constant BASELINE_MAX. */
    private final static int BASELINE_MAX = 255;
    
    /** The Constant MAX. */
    private final static int MAX = 32767;


    /** The table. */
    private int[] theTable;

    /*
     * K1 & K2 tables can be found in the JPEG format specification 
     * at http://www.w3.org/Graphics/JPEG/itu-t81.pdf
     */

    /** The Constant K1LumTable. */
    private static final int[] K1LumTable = new int[] {
        16,  11,  10,  16,  24,  40,  51,  61,
        12,  12,  14,  19,  26,  58,  60,  55,
        14,  13,  16,  24,  40,  57,  69,  56,
        14,  17,  22,  29,  51,  87,  80,  62,
        18,  22,  37,  56,  68,  109, 103, 77,
        24,  35,  55,  64,  81,  104, 113, 92,
        49,  64,  78,  87,  103, 121, 120, 101,
        72,  92,  95,  98,  112, 100, 103, 99
    };

    /** The Constant K2ChrTable. */
    private static final int[] K2ChrTable = new int[] {
        17,  18,  24,  47,  99,  99,  99,  99,
        18,  21,  26,  66,  99,  99,  99,  99,
        24,  26,  56,  99,  99,  99,  99,  99,
        47,  66,  99,  99,  99,  99,  99,  99,
        99,  99,  99,  99,  99,  99,  99,  99,
        99,  99,  99,  99,  99,  99,  99,  99,
        99,  99,  99,  99,  99,  99,  99,  99,
        99,  99,  99,  99,  99,  99,  99,  99
    };

    /** 
     * The K1Luminance indicates standart table K.1 from JPEG
     * specification and produces "good" quality output. 
     */
    public static final JPEGQTable K1Luminance = new JPEGQTable(K1LumTable);
    
    /** 
     * The K1Div2Luminance indicates K.1 table from JPEG
     * specification with all elements divided by 2 and produces
     * "very good" quality output. 
     */
    public static final JPEGQTable K1Div2Luminance = K1Luminance.getScaledInstance(0.5f, true);
    
    /** 
     * The K2Chrominance indicates K.2 table from JPEG
     * specification and produces "good" quality output. 
     */
    public static final JPEGQTable K2Chrominance = new JPEGQTable(K2ChrTable);
    
    /** 
     * The Constant K2Div2Chrominance indicates K.2 table from JPEG
     * specification with all elements divided by 2 and produces
     * "very good" quality output. 
     */
    public static final JPEGQTable K2Div2Chrominance = K2Chrominance.getScaledInstance(0.5f, true);;


    /**
     * Instantiates a new JPEGQTable from the array, which 
     * should contain 64 elements in natural order.
     * 
     * @param table the quantization table.
     */
    public JPEGQTable(int[] table) {
        if (table == null) {
            throw new IllegalArgumentException("table should not be NULL");
        }
        if (table.length != SIZE) {
            throw new IllegalArgumentException("illegal table size: " + table.length);
        }
        theTable = table.clone();
    }

    /**
     * Gets the current quantization table as an array of int values.
     * 
     * @return the current quantization table as an array of int values.
     */
    public int[] getTable() {
        return theTable.clone();
    }

    /**
     * Gets the scaled instance as quantization table where 
     * the values are multiplied by the scaleFactor and then clamped 
     * if forceBaseline is true.
     * 
     * @param scaleFactor the scale factor of table.
     * @param forceBaseline the force baseline flag, the values 
     * should be clamped if true.
     * 
     * @return the new quantization table.
     */
    public JPEGQTable getScaledInstance(float scaleFactor, boolean forceBaseline) {
        int table[] = new int[SIZE];

        int maxValue = forceBaseline ? BASELINE_MAX : MAX;

        for (int i = 0; i < theTable.length; i++) {
            int rounded = Math.round(theTable[i] * scaleFactor);
            if (rounded < 1) {
                rounded = 1;
            }
            if (rounded > maxValue) {
                rounded = maxValue;
            }
            table[i] = rounded;
        }
        return new JPEGQTable(table);
    }

    /**
     * Returns the string representation of this JPEGQTable object.
     * 
     * @return the string representation of this JPEGQTable object.
     */
    @Override
    public String toString() {
        //-- TODO more informative info
        return "JPEGQTable";
    }
}