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package javax.imageio.plugins.jpeg;

import java.util.Arrays;


A class encapsulating a single JPEG quantization table.
The elements appear in natural order (as opposed to zig-zag order).
Static variables are provided for the "standard" tables taken from
 Annex K of the JPEG specification, as well as the default tables
conventionally used for visually lossless encoding.


For more information about the operation of the standard JPEG plug-in,
see the JPEG
metadata format specification and usage notes

/**
 * A class encapsulating a single JPEG quantization table.
 * The elements appear in natural order (as opposed to zig-zag order).
 * Static variables are provided for the "standard" tables taken from
 *  Annex K of the JPEG specification, as well as the default tables
 * conventionally used for visually lossless encoding.
 * <p>
 * For more information about the operation of the standard JPEG plug-in,
 * see the <A HREF="../../metadata/doc-files/jpeg_metadata.html">JPEG
 * metadata format specification and usage notes</A>
 */

public class JPEGQTable {

    private static final int[] k1 = {
        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,
    };

    private static final int[] k1div2 = {
        8,   6,   5,   8,   12,  20,  26,  31,
        6,   6,   7,   10,  13,  29,  30,  28,
        7,   7,   8,   12,  20,  29,  35,  28,
        7,   9,   11,  15,  26,  44,  40,  31,
        9,   11,  19,  28,  34,  55,  52,  39,
        12,  18,  28,  32,  41,  52,  57,  46,
        25,  32,  39,  44,  52,  61,  60,  51,
        36,  46,  48,  49,  56,  50,  52,  50,
    };

    private static final int[] k2 = {
        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,
    };

    private static final int[] k2div2 = {
        9,   9,   12,  24,  50,  50,  50,  50,
        9,   11,  13,  33,  50,  50,  50,  50,
        12,  13,  28,  50,  50,  50,  50,  50,
        24,  33,  50,  50,  50,  50,  50,  50,
        50,  50,  50,  50,  50,  50,  50,  50,
        50,  50,  50,  50,  50,  50,  50,  50,
        50,  50,  50,  50,  50,  50,  50,  50,
        50,  50,  50,  50,  50,  50,  50,  50,
    };

    
The sample luminance quantization table given in the JPEG
specification, table K.1. According to the specification,
these values produce "good" quality output.

See Also:
  • K1Div2Luminance
/**
     * The sample luminance quantization table given in the JPEG
     * specification, table K.1. According to the specification,
     * these values produce "good" quality output.
     * @see #K1Div2Luminance
     */
    public static final JPEGQTable
        K1Luminance = new JPEGQTable(k1, false);

    
The sample luminance quantization table given in the JPEG
specification, table K.1, with all elements divided by 2.
According to the specification, these values produce "very good"
quality output. This is the table usually used for "visually lossless"
encoding, and is the default luminance table used if the default
tables and quality settings are used.

See Also:
  • K1Luminance
/**
     * The sample luminance quantization table given in the JPEG
     * specification, table K.1, with all elements divided by 2.
     * According to the specification, these values produce "very good"
     * quality output. This is the table usually used for "visually lossless"
     * encoding, and is the default luminance table used if the default
     * tables and quality settings are used.
     * @see #K1Luminance
     */
    public static final JPEGQTable
        K1Div2Luminance = new JPEGQTable(k1div2, false);

    
The sample chrominance quantization table given in the JPEG
specification, table K.2. According to the specification,
these values produce "good" quality output.

See Also:
  • K2Div2Chrominance
/**
     * The sample chrominance quantization table given in the JPEG
     * specification, table K.2. According to the specification,
     * these values produce "good" quality output.
     * @see #K2Div2Chrominance
     */
    public static final JPEGQTable K2Chrominance =
        new JPEGQTable(k2, false);

    
The sample chrominance quantization table given in the JPEG
specification, table K.1, with all elements divided by 2.
According to the specification, these values produce "very good"
quality output. This is the table usually used for "visually lossless"
encoding, and is the default chrominance table used if the default
tables and quality settings are used.

See Also:
  • K2Chrominance
/**
     * The sample chrominance quantization table given in the JPEG
     * specification, table K.1, with all elements divided by 2.
     * According to the specification, these values produce "very good"
     * quality output. This is the table usually used for "visually lossless"
     * encoding, and is the default chrominance table used if the default
     * tables and quality settings are used.
     * @see #K2Chrominance
     */
    public static final JPEGQTable K2Div2Chrominance =
        new JPEGQTable(k2div2, false);

    private int[] qTable;

    private JPEGQTable(int[] table, boolean copy) {
        qTable = (copy) ? Arrays.copyOf(table, table.length) : table;
    }

    
Constructs a quantization table from the argument, which must
contain 64 elements in natural order (not zig-zag order).
A copy is made of the input array.

Params:
  • table – the quantization table, as an int array.
Throws:
/**
     * Constructs a quantization table from the argument, which must
     * contain 64 elements in natural order (not zig-zag order).
     * A copy is made of the input array.
     * @param table the quantization table, as an {@code int} array.
     * @throws IllegalArgumentException if {@code table} is
     * {@code null} or {@code table.length} is not equal to 64.
     */
    public JPEGQTable(int[] table) {
        if (table == null) {
            throw new IllegalArgumentException("table must not be null.");
        }
        if (table.length != 64) {
            throw new IllegalArgumentException("table.length != 64");
        }
        qTable = Arrays.copyOf(table, table.length);
    }

    
Returns a copy of the current quantization table as an array of ints in natural (not zig-zag) order. 
Returns:A copy of the current quantization table.
/**
     * Returns a copy of the current quantization table as an array
     * of {@code int}s in natural (not zig-zag) order.
     * @return A copy of the current quantization table.
     */
    public int[] getTable() {
        return Arrays.copyOf(qTable, qTable.length);
    }

    
Returns a new quantization table where the values are multiplied by scaleFactor and then clamped to the range 1..32767 (or to 1..255 if forceBaseline is true). 
 Values of scaleFactor less than 1 tend to improve the quality level of the table, and values greater than 1.0 degrade the quality level of the table. 
Params:
  • scaleFactor – multiplication factor for the table.
  • forceBaseline – if true, the values will be clamped to the range 1..255
Returns:a new quantization table that is a linear multiple
of the current table.
/**
     * Returns a new quantization table where the values are multiplied
     * by {@code scaleFactor} and then clamped to the range 1..32767
     * (or to 1..255 if {@code forceBaseline} is true).
     * <p>
     * Values of {@code scaleFactor} less than 1 tend to improve
     * the quality level of the table, and values greater than 1.0
     * degrade the quality level of the table.
     * @param scaleFactor multiplication factor for the table.
     * @param forceBaseline if {@code true},
     * the values will be clamped to the range 1..255
     * @return a new quantization table that is a linear multiple
     * of the current table.
     */
    public JPEGQTable getScaledInstance(float scaleFactor,
                                        boolean forceBaseline) {
        int max = (forceBaseline) ? 255 : 32767;
        int[] scaledTable = new int[qTable.length];
        for (int i=0; i<qTable.length; i++) {
            int sv = (int)((qTable[i] * scaleFactor)+0.5f);
            if (sv < 1) {
                sv = 1;
            }
            if (sv > max) {
                sv = max;
            }
            scaledTable[i] = sv;
        }
        return new JPEGQTable(scaledTable);
    }

    
Returns a String representing this quantization table. 
Returns:a String representing this quantization table.
/**
     * Returns a {@code String} representing this quantization table.
     * @return a {@code String} representing this quantization table.
     */
    public String toString() {
        String ls = System.getProperty("line.separator", "\n");
        StringBuilder sb = new StringBuilder("JPEGQTable:"+ls);
        for (int i=0; i < qTable.length; i++) {
            if (i % 8 == 0) {
                sb.append('\t');
            }
            sb.append(qTable[i]);
            sb.append(((i % 8) == 7) ? ls : ' ');
        }
        return sb.toString();
    }
}