pngencoder.java

该源代码为一些通用的程序

package com.keypoint;

import java.awt.Image;
import java.awt.image.ImageObserver;
import java.awt.image.PixelGrabber;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.zip.CRC32;
import java.util.zip.Deflater;
import java.util.zip.DeflaterOutputStream;

/**
 * PngEncoder takes a Java Image object and creates a byte string which can be 
 * saved as a PNG file.  The Image is presumed to use the DirectColorModel.
 *
 * <p>Thanks to Jay Denny at KeyPoint Software
 *    http://www.keypoint.com/
 * who let me develop this code on company time.</p>
 *
 * <p>You may contact me with (probably very-much-needed) improvements,
 * comments, and bug fixes at:</p>
 *
 *   <p><code>[e-mail]</code></p>
 *
 * <p>This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.</p>
 *
 * <p>This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.</p>
 *
 * <p>You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA. A copy of the GNU LGPL may be found at
 * <code>http://www.gnu.org/copyleft/lesser.html</code></p>
 *
 * @author J. David Eisenberg
 * @version 1.5, 19 Oct 2003
 *
 * CHANGES:
 * --------
 * 19-Nov-2002 : CODING STYLE CHANGES ONLY (by David Gilbert for Object 
 *               Refinery Limited);
 * 19-Sep-2003 : Fix for platforms using EBCDIC (contributed by Paulo Soares);
 * 19-Oct-2003 : Change private fields to protected fields so that
 *               PngEncoderB can inherit them (JDE)
 *               Fixed bug with calculation of nRows
 */

public class PngEncoder {

    /** Constant specifying that alpha channel should be encoded. */
    public static final boolean ENCODE_ALPHA = true;

    /** Constant specifying that alpha channel should not be encoded. */
    public static final boolean NO_ALPHA = false;

    /** Constants for filter (NONE). */
    public static final int FILTER_NONE = 0;

    /** Constants for filter (SUB). */
    public static final int FILTER_SUB = 1;

    /** Constants for filter (UP). */
    public static final int FILTER_UP = 2;

    /** Constants for filter (LAST). */
    public static final int FILTER_LAST = 2;
    
    /** IHDR tag. */
    protected static final byte[] IHDR = {73, 72, 68, 82};
    
    /** IDAT tag. */
    protected static final byte[] IDAT = {73, 68, 65, 84};
    
    /** IEND tag. */
    protected static final byte[] IEND = {73, 69, 78, 68};

    protected static final byte[] PHYS = {(byte)'p', (byte)'H', (byte)'Y', (byte)'s'};

    /** The png bytes. */
    protected byte[] pngBytes;

    /** The prior row. */
    protected byte[] priorRow;

    /** The left bytes. */
    protected byte[] leftBytes;

    /** The image. */
    protected Image image;

    /** The width. */
    protected int width;

    /** The height. */
    protected int height;

    /** The byte position. */
    protected int bytePos;

    /** The maximum position. */
    protected int maxPos;

    /** CRC. */
    protected CRC32 crc = new CRC32();

    /** The CRC value. */
    protected long crcValue;

    /** Encode alpha? */
    protected boolean encodeAlpha;

    /** The filter type. */
    protected int filter;

    /** The bytes-per-pixel. */
    protected int bytesPerPixel;

    /** The physical pixel dimension : number of pixels per inch on the X axis. */
    private int xDpi = 0;

    /** The physical pixel dimension : number of pixels per inch on the Y axis. */
    private int yDpi = 0;

    /** Used for conversion of DPI to Pixels per Meter. */
    static private float INCH_IN_METER_UNIT = 0.0254f;

    /** 
     * The compression level (1 = best speed, 9 = best compression, 
     * 0 = no compression). 
     */
    protected int compressionLevel;

    /**
     * Class constructor.
     */
    public PngEncoder() {
        this(null, false, FILTER_NONE, 0);
    }

    /**
     * Class constructor specifying Image to encode, with no alpha channel 
     * encoding.
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @see java.awt.Image
     */
    public PngEncoder(Image image) {
        this(image, false, FILTER_NONE, 0);
    }

    /**
     * Class constructor specifying Image to encode, and whether to encode 
     * alpha.
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
     * @see java.awt.Image
     */
    public PngEncoder(Image image, boolean encodeAlpha) {
        this(image, encodeAlpha, FILTER_NONE, 0);
    }

    /**
     * Class constructor specifying Image to encode, whether to encode alpha, 
     * and filter to use.
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
     * @param whichFilter 0=none, 1=sub, 2=up
     * @see java.awt.Image
     */
    public PngEncoder(Image image, boolean encodeAlpha, int whichFilter) {
        this(image, encodeAlpha, whichFilter, 0);
    }


    /**
     * Class constructor specifying Image source to encode, whether to encode 
     * alpha, filter to use, and compression level.
     *
     * @param image A Java Image object
     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
     * @param whichFilter 0=none, 1=sub, 2=up
     * @param compLevel 0..9 (1 = best speed, 9 = best compression, 0 = no 
     *        compression)
     * @see java.awt.Image
     */
    public PngEncoder(Image image, boolean encodeAlpha, int whichFilter, 
            int compLevel) {
        this.image = image;
        this.encodeAlpha = encodeAlpha;
        setFilter(whichFilter);
        if (compLevel >= 0 && compLevel <= 9) {
            this.compressionLevel = compLevel;
        }
    }

    /**
     * Set the image to be encoded.
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @see java.awt.Image
     * @see java.awt.image.DirectColorModel
     */
    public void setImage(Image image) {
        this.image = image;
        this.pngBytes = null;
    }

    /**
     * Returns the image to be encoded.
     */
    public Image getImage() {
      return image;
    }

  /**
     * Creates an array of bytes that is the PNG equivalent of the current 
     * image, specifying whether to encode alpha or not.
     *
     * @param encodeAlpha boolean false=no alpha, true=encode alpha
     * @return an array of bytes, or null if there was a problem
     */
    public byte[] pngEncode(boolean encodeAlpha) {
        byte[]  pngIdBytes = {-119, 80, 78, 71, 13, 10, 26, 10};

        if (this.image == null) {
            return null;
        }
        this.width = this.image.getWidth(null);
        this.height = this.image.getHeight(null);

        /*
         * start with an array that is big enough to hold all the pixels
         * (plus filter bytes), and an extra 200 bytes for header info
         */
        this.pngBytes = new byte[((this.width + 1) * this.height * 3) + 200];

        /*
         * keep track of largest byte written to the array
         */
        this.maxPos = 0;

        this.bytePos = writeBytes(pngIdBytes, 0);
        //hdrPos = bytePos;
        writeHeader();
        writeResolution();
        //dataPos = bytePos;
        if (writeImageData()) {
            writeEnd();
            this.pngBytes = resizeByteArray(this.pngBytes, this.maxPos);
        }
        else {
            this.pngBytes = null;
        }
        return this.pngBytes;
    }

    /**
     * Creates an array of bytes that is the PNG equivalent of the current 
     * image.  Alpha encoding is determined by its setting in the constructor.
     *
     * @return an array of bytes, or null if there was a problem
     */
    public byte[] pngEncode() {
        return pngEncode(this.encodeAlpha);
    }

    /**
     * Set the alpha encoding on or off.
     *
     * @param encodeAlpha  false=no, true=yes
     */
    public void setEncodeAlpha(boolean encodeAlpha) {
        this.encodeAlpha = encodeAlpha;
    }

    /**
     * Retrieve alpha encoding status.
     *
     * @return boolean false=no, true=yes
     */
    public boolean getEncodeAlpha() {
        return this.encodeAlpha;
    }

    /**
     * Set the filter to use.
     *
     * @param whichFilter from constant list
     */
    public void setFilter(int whichFilter) {
        this.filter = FILTER_NONE;
        if (whichFilter <= FILTER_LAST) {
            this.filter = whichFilter;
        }
    }

    /**
     * Retrieve filtering scheme.
     *
     * @return int (see constant list)
     */
    public int getFilter() {
        return this.filter;
    }

    /**
     * Set the compression level to use.
     *
     * @param level the compression level (1 = best speed, 9 = best compression,
     *        0 = no compression)
     */
    public void setCompressionLevel(int level) {
        if (level >= 0 && level <= 9) {
            this.compressionLevel = level;
        }
    }

    /**
     * Retrieve compression level.
     *
     * @return int (1 = best speed, 9 = best compression, 0 = no compression)
     */
    public int getCompressionLevel() {
        return this.compressionLevel;
    }

    /**
     * Increase or decrease the length of a byte array.
     *
     * @param array The original array.
     * @param newLength The length you wish the new array to have.
     * @return Array of newly desired length. If shorter than the
     *         original, the trailing elements are truncated.
     */
    protected byte[] resizeByteArray(byte[] array, int newLength) {
        byte[]  newArray = new byte[newLength];
        int     oldLength = array.length;

        System.arraycopy(array, 0, newArray, 0, Math.min(oldLength, newLength));
        return newArray;
    }

    /**
     * Write an array of bytes into the pngBytes array.
     * Note: This routine has the side effect of updating
     * maxPos, the largest element written in the array.
     * The array is resized by 1000 bytes or the length
     * of the data to be written, whichever is larger.