pngencoder.java

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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.
 *
 * Thanks to Jay Denny at KeyPoint Software
 *    http://www.keypoint.com/
 * who let me develop this code on company time.
 *
 * You may contact me with (probably very-much-needed) improvements,
 * comments, and bug fixes at:
 *
 *   [e-mail]
 *
 * 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.
 *
 * 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.
 *
 * 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * A copy of the GNU LGPL may be found at
 * http://www.gnu.org/copyleft/lesser.html,
 *
 * @author J. David Eisenberg
 * @version 1.4, 31 March 2000
 *
 * MODIFIED BY DAVID GILBERT ON 19-NOV-2002 (CODING STYLE CHANGES ONLY).
 *
 */
public class PngEncoder extends Object {

    /** 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;

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

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

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

    /** The image. */
    private Image image;

    /** The width. */
    private int width, height;

    /** The byte position. */
    private int bytePos, maxPos;

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

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

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

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

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

    /** The compression level. */
    private 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
     * @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;
        pngBytes = null;
    }

    /**
     * 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 (image == null) {
            return null;
        }
        width = image.getWidth(null);
        height = 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
         */
        pngBytes = new byte[((width + 1) * height * 3) + 200];

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

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

    /**
     * Set the compression level to use
     *
     * @param level 0 through 9
     */
    public void setCompressionLevel(int level) {
        if (level >= 0 && level <= 9) {
            this.compressionLevel = level;
        }
    }

    /**
     * Retrieve compression level
     *
     * @return int in range 0-9
     */
    public int getCompressionLevel() {
        return 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;
    }

    /**