Module java.desktop
Package javax.imageio.plugins.jpeg

Class JPEGQTable

  • public class JPEGQTable
extends Object
    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

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static JPEGQTable K1Div2Luminance
      The sample luminance quantization table given in the JPEG specification, table K.1, with all elements divided by 2.
      static JPEGQTable K1Luminance
      The sample luminance quantization table given in the JPEG specification, table K.1.
      static JPEGQTable K2Chrominance
      The sample chrominance quantization table given in the JPEG specification, table K.2.
      static JPEGQTable K2Div2Chrominance
      The sample chrominance quantization table given in the JPEG specification, table K.1, with all elements divided by 2.

    • Constructor Summary

      Constructors 
      Constructor Description
      JPEGQTable​(int[] table)
      Constructs a quantization table from the argument, which must contain 64 elements in natural order (not zig-zag order).

    • Method Summary

      Modifier and Type Method Description
      JPEGQTable getScaledInstance​(float scaleFactor, boolean forceBaseline)
      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).
      int[] getTable()
      Returns a copy of the current quantization table as an array of ints in natural (not zig-zag) order.
      String toString()
      Returns a String representing this quantization table.

    • Field Detail

      • K1Luminance

        public static final JPEGQTable K1Luminance
        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

      • K1Div2Luminance

        public static final JPEGQTable K1Div2Luminance
        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

      • K2Chrominance

        public static final JPEGQTable K2Chrominance
        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

      • K2Div2Chrominance

        public static final JPEGQTable K2Div2Chrominance
        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

    • Constructor Detail

      • JPEGQTable

        public JPEGQTable​(int[] 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.
        Parameters:
        table - the quantization table, as an int array.
        Throws:
        IllegalArgumentException - if table is null or table.length is not equal to 64.

    • Method Detail

      • getTable

        public int[] getTable()
        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.

      • getScaledInstance

        public JPEGQTable getScaledInstance​(float scaleFactor,
                                    boolean forceBaseline)
        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.

        Parameters:
        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.

      • toString

        public String toString()
        Returns a String representing this quantization table.
        Overrides:
        toString in class Object
        Returns:
        a String representing this quantization table.