jpegqtable.java

java1.6众多例子参考

/*
 * @(#)JPEGQTable.java	1.10 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

/**********************************************************************
 **********************************************************************
 **********************************************************************
 *** COPYRIGHT (c) 1997-1998 Eastman Kodak Company.                 ***
 *** As  an unpublished  work pursuant to Title 17 of the United    ***
 *** States Code.  All rights reserved.                             ***
 **********************************************************************
 **********************************************************************
 **********************************************************************/

package com.sun.image.codec.jpeg;



/** Class to encapsulate the JPEG quantization tables.
 * <p>
 * Note that the classes in the com.sun.image.codec.jpeg package are not
 * part of the core Java APIs.  They are a part of Sun's JDK and JRE
 * distributions.  Although other licensees may choose to distribute these
 * classes, developers cannot depend on their availability in non-Sun
 * implementations.  We expect that equivalent functionality will eventually
 * be available in a core API or standard extension.
 * <p>
 */
public class JPEGQTable {

	/** Quantization step for each coefficient in zig-zag order */
	private int quantval[];

	/** The number of coefficients in a DCT block */
	private static final byte QTABLESIZE = 64;
	
	/** 
	 * This is the sample luminance quantization table given in the
	 * JPEG spec section K.1, expressed in zigzag order. The spec says
	 * that the values given produce "good" quality, and when divided
	 * by 2, "very good" quality.
	 */
	public static final JPEGQTable StdLuminance = new JPEGQTable();
	static {
		int [] lumVals = {
			16,   11,  12,  14,  12,  10,  16,  14,
			13,   14,  18,  17,  16,  19,  24,  40,
			26,   24,  22,  22,  24,  49,  35,  37,
			29,   40,  58,  51,  61,  60,  57,  51,
			56,   55,  64,  72,  92,  78,  64,  68,
			87,   69,  55,  56,  80, 109,  81,  87,
			95,   98, 103, 104, 103,  62,  77, 113,
			121, 112, 100, 120,  92, 101, 103,  99
		};
		
		StdLuminance.quantval = lumVals;
	}

	/** 
	 * This is the sample luminance quantization table given in the
	 * JPEG spec section K.1, expressed in zigzag order. The spec says
	 * that the values given produce "good" quality, and when divided
	 * by 2, "very good" quality.
	 */
	public static final JPEGQTable StdChrominance = new JPEGQTable();
	static {
		int [] chromVals = {
			17,  18,  18,  24,  21,  24,  47,  26,
			26,  47,  99,  66,  56,  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,  99,  99,  99,  99,
			99,  99,  99,  99,  99,  99,  99,  99
		};
		StdChrominance.quantval = chromVals;
	}
		

	/** 
	 * Constructs an empty quantization table. This is used to create
	 * the Std Q-Tables.
	 */
	private JPEGQTable() {
		quantval = new int[QTABLESIZE];
	}
		
	/** 
	 * Constructs an quantization table from the array that was
	 * passed.  The coefficents must be in zig-zag order. The array
	 * must be of length 64.
	 *  @param table the quantization table (this is copied).
	 */
	public JPEGQTable( int table[] ) {
		if ( table.length != QTABLESIZE ) {
			throw new IllegalArgumentException
				("Quantization table is the wrong size.");
		} else {
			quantval = new int[QTABLESIZE];
			System.arraycopy( table, 0, quantval, 0, QTABLESIZE );
		}
	}
		

	/** 
	 * Returns the current quantization table as an array of ints in
	 * zig zag order.
	 *  @return A copy of the contained quantization table.
	 */
	public int[] getTable() { 
		int[] table = new int[QTABLESIZE];
		System.arraycopy( quantval, 0, table, 0, QTABLESIZE );
		return table;
	}

	/** 
	 * 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'). <P>

	 * Values less than one tend to improve the quality level of the
	 * table, and values greater than one degrade the quality level of
	 * the table.

	 * @param scaleFactor the multiplication factor for the table
	 * @param forceBaseline if true the values will be clamped
	 * to the range  [1 .. 255]
	 * @return A new Q-Table that is a linear multiple of this Q-Table
	 */
	public JPEGQTable getScaledInstance(float scaleFactor, 
										boolean forceBaseline ) {
		long  max    = (forceBaseline)?255L:32767L;
		int []ret    = new int[QTABLESIZE];

		for (int i=0; i<QTABLESIZE; i++ ) {
			long holder = (long)((quantval[i] * scaleFactor) + 0.5);

			// limit to valid range
			if (holder <= 0L) holder = 1L;

			// Max quantizer for 12 bits
			if (holder > max ) holder = max; 
			
			ret[i] = (int)holder;
		}
		return new JPEGQTable(ret);
	}
}