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PngEncoder.java

package rene.util;

/**
 * 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:
 *
 *   david@catcode.com
 *
 * 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
 */

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;

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 filters */
    public static final int FILTER_NONE = 0;
    public static final int FILTER_SUB = 1;
    public static final int FILTER_UP = 2;
    public static final int FILTER_LAST = 2;

    protected byte[] pngBytes;
    protected byte[] priorRow;
    protected byte[] leftBytes;
    protected Image image;
    protected int width, height;
    protected int bytePos, maxPos;
    protected int hdrPos, dataPos, endPos;
    protected CRC32 crc = new CRC32();
    protected long crcValue;
    protected boolean encodeAlpha;
    protected int filter;
    protected int bytesPerPixel;
    protected int compressionLevel;
    protected double DPI=300;

    /**
     * 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;
    }
    
    public void setDPI (double dpi)
    { DPI=dpi;
    }

    /**
     * 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 };
        int     i;

        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();
            writePhys();
            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;
    }

    /**
     * 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.
     *
     * @param data The data to be written into pngBytes.
     * @param offset The starting point to write to.
     * @return The next place to be written to in the pngBytes array.
     */
    protected int writeBytes( byte[] data, int offset )
    {
        maxPos = Math.max( maxPos, offset + data.length );
        if (data.length + offset > pngBytes.length)
        {
            pngBytes = resizeByteArray( pngBytes, pngBytes.length +
                Math.max( 1000, data.length ) );
        }
        System.arraycopy( data, 0, pngBytes, offset, data.length );
        return offset + data.length;
    }

    /**
     * Write an array of bytes into the pngBytes array, specifying number of bytes to write.
     * 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.
     *
     * @param data The data to be written into pngBytes.
     * @param nBytes The number of bytes to be written.
     * @param offset The starting point to write to.
     * @return The next place to be written to in the pngBytes array.
     */
    protected int writeBytes( byte[] data, int nBytes, int offset )
    {
        maxPos = Math.max( maxPos, offset + nBytes );
        if (nBytes + offset > pngBytes.length)
        {
            pngBytes = resizeByteArray( pngBytes, pngBytes.length +
                Math.max( 1000, nBytes ) );
        }
        System.arraycopy( data, 0, pngBytes, offset, nBytes );
        return offset + nBytes;
    }

    /**
     * Write a two-byte integer into the pngBytes array at a given position.
     *
     * @param n The integer to be written into pngBytes.
     * @param offset The starting point to write to.
     * @return The next place to be written to in the pngBytes array.
     */
    protected int writeInt2( int n, int offset )
    {
        byte[] temp = { (byte)((n >> 8) & 0xff),
            (byte) (n & 0xff) };
        return writeBytes( temp, offset );
    }

    /**
     * Write a four-byte integer into the pngBytes array at a given position.
     *
     * @param n The integer to be written into pngBytes.
     * @param offset The starting point to write to.
     * @return The next place to be written to in the pngBytes array.
     */
    protected int writeInt4( int n, int offset )
    {
        byte[] temp = { (byte)((n >> 24) & 0xff),
            (byte) ((n >> 16) & 0xff ),
            (byte) ((n >> 8) & 0xff ),
            (byte) ( n & 0xff ) };
        return writeBytes( temp, offset );
    }

    /**
     * Write a single byte into the pngBytes array at a given position.
     *
     * @param n The integer to be written into pngBytes.
     * @param offset The starting point to write to.
     * @return The next place to be written to in the pngBytes array.
     */
    protected int writeByte( int b, int offset )
    {
        byte[] temp = { (byte) b };
        return writeBytes( temp, offset );
    }

    /**
     * Write a string into the pngBytes array at a given position.
     * This uses the getBytes method, so the encoding used will
     * be its default.
     *
     * @param n The integer to be written into pngBytes.
     * @param offset The starting point to write to.
     * @return The next place to be written to in the pngBytes array.
     * @see java.lang.String#getBytes()
     */
    protected int writeString( String s, int offset )
    {
        return writeBytes( s.getBytes(), offset );
    }

    /**
     * Write a PNG "IHDR" chunk into the pngBytes array.
     */
    protected void writeHeader()
    {
        int startPos;

        startPos = bytePos = writeInt4( 13, bytePos );
        bytePos = writeString( "IHDR", bytePos );
        width = image.getWidth( null );
        height = image.getHeight( null );
        bytePos = writeInt4( width, bytePos );
        bytePos = writeInt4( height, bytePos );
        bytePos = writeByte( 8, bytePos ); // bit depth
        bytePos = writeByte( (encodeAlpha) ? 6 : 2, bytePos ); // direct model
        bytePos = writeByte( 0, bytePos ); // compression method
        bytePos = writeByte( 0, bytePos ); // filter method
        bytePos = writeByte( 0, bytePos ); // no interlace
        crc.reset();
        crc.update( pngBytes, startPos, bytePos-startPos );
        crcValue = crc.getValue();
        bytePos = writeInt4( (int) crcValue, bytePos );
    }

      /**
       * Write a PNG "pHYs" chunk into the pngBytes array.
       */
      protected void writePhys()
      {
            int startPos;

            startPos = bytePos = writeInt4( 9, bytePos );
            bytePos = writeString( "pHYs", bytePos );
            int dots=(int)(DPI*39.37);
            bytePos = writeInt4( dots, bytePos );
            bytePos = writeInt4( dots, bytePos );
            bytePos = writeByte( 1, bytePos ); // bit depth
            crc.reset();
            crc.update( pngBytes, startPos, bytePos-startPos );
            crcValue = crc.getValue();
            bytePos = writeInt4( (int) crcValue, bytePos );
      }

    /**
     * Perform "sub" filtering on the given row.
     * Uses temporary array leftBytes to store the original values
     * of the previous pixels.  The array is 16 bytes long, which
     * will easily hold two-byte samples plus two-byte alpha.
     *
     * @param pixels The array holding the scan lines being built
     * @param startPos Starting position within pixels of bytes to be filtered.
     * @param width Width of a scanline in pixels.
     */
    protected void filterSub( byte[] pixels, int startPos, int width )
    {
        int i;
        int offset = bytesPerPixel;
        int actualStart = startPos + offset;
        int nBytes = width * bytesPerPixel;
        int leftInsert = offset;
        int leftExtract = 0;
        byte current_byte;

        for (i=actualStart; i < startPos + nBytes; i++)
        {
            leftBytes[leftInsert] =  pixels[i];
            pixels[i] = (byte) ((pixels[i] - leftBytes[leftExtract]) % 256);
            leftInsert = (leftInsert+1) % 0x0f;
            leftExtract = (leftExtract + 1) % 0x0f;
        }
    }

    /**
     * Perform "up" filtering on the given row.
     * Side effect: refills the prior row with current row
     *
     * @param pixels The array holding the scan lines being built
     * @param startPos Starting position within pixels of bytes to be filtered.
     * @param width Width of a scanline in pixels.
     */
    protected void filterUp( byte[] pixels, int startPos, int width )
    {
        int     i, nBytes;
        byte    current_byte;

        nBytes = width * bytesPerPixel;

        for (i=0; i < nBytes; i++)
        {
            current_byte = pixels[startPos + i];
            pixels[startPos + i] = (byte) ((pixels[startPos  + i] - priorRow[i]) % 256);
            priorRow[i] = current_byte;
        }
    }

    /**
     * Write the image data into the pngBytes array.
     * This will write one or more PNG "IDAT" chunks. In order
     * to conserve memory, this method grabs as many rows as will
     * fit into 32K bytes, or the whole image; whichever is less.
     *
     *
     * @return true if no errors; false if error grabbing pixels
     */
    protected boolean writeImageData()
    {
        int rowsLeft = height;  // number of rows remaining to write
        int startRow = 0;       // starting row to process this time through
        int nRows;              // how many rows to grab at a time

        byte[] scanLines;       // the scan lines to be compressed
        int scanPos;            // where we are in the scan lines
        int startPos;           // where this line's actual pixels start (used for filtering)

        byte[] compressedLines; // the resultant compressed lines
        int nCompressed;        // how big is the compressed area?

        int depth;              // color depth ( handle only 8 or 32 )

        PixelGrabber pg;

        bytesPerPixel = (encodeAlpha) ? 4 : 3;

        Deflater scrunch = new Deflater( compressionLevel );
        ByteArrayOutputStream outBytes = 
            new ByteArrayOutputStream(1024);
            
        DeflaterOutputStream compBytes =
            new DeflaterOutputStream( outBytes, scrunch );
        try
        {
            nRows = (64*32768-1) / (width*(bytesPerPixel+1));
            
            int[] pixels = new int[width * nRows];

            while (rowsLeft > 0)
            {
                  if (nRows>=rowsLeft) nRows=rowsLeft;
                  
                 pg = new PixelGrabber(image, 0, startRow,
                    width, nRows, pixels, 0, width);
                try {
                    pg.grabPixels();
                }
                catch (Exception e) {
                    System.err.println("interrupted waiting for pixels!");
                    return false;
                }
                if ((pg.getStatus() & ImageObserver.ABORT) != 0) {
                    System.err.println("image fetch aborted or errored");
                    return false;
                }

                /*
                 * Create a data chunk. scanLines adds "nRows" for
                 * the filter bytes. 
                 */
                scanLines = new byte[width * nRows * bytesPerPixel +  nRows];

                if (filter == FILTER_SUB)
                {
                    leftBytes = new byte[16];
                }
                if (filter == FILTER_UP)
                {
                    priorRow = new byte[width*bytesPerPixel];
                }

                scanPos = 0;
                startPos = 1;
                for (int i=0; i<width*nRows; i++)
                {
                    if (i % width == 0)
                    {
                        scanLines[scanPos++] = (byte) filter; 
                        startPos = scanPos;
                    }
                    scanLines[scanPos++] = (byte) ((pixels[i] >> 16) & 0xff);
                    scanLines[scanPos++] = (byte) ((pixels[i] >>  8) & 0xff);
                    scanLines[scanPos++] = (byte) ((pixels[i]      ) & 0xff);
                    if (encodeAlpha)
                    {
                        scanLines[scanPos++] = (byte) ((pixels[i] >> 24) & 0xff );
                    }
                    if ((i % width == width-1) && (filter != FILTER_NONE))
                    {
                        if (filter == FILTER_SUB)
                        {
                            filterSub( scanLines, startPos, width );
                        }
                        if (filter == FILTER_UP)
                        {
                            filterUp( scanLines, startPos, width );
                        }
                    }
                }

                /*
                 * Write these lines to the output area
                 */
                compBytes.write( scanLines, 0, scanPos );


                startRow += nRows;
                rowsLeft -= nRows;
            }
            compBytes.close();

            /*
             * Write the compressed bytes
             */
            compressedLines = outBytes.toByteArray();
            nCompressed = compressedLines.length;

            crc.reset();
            bytePos = writeInt4( nCompressed, bytePos );
            bytePos = writeString("IDAT", bytePos );
            crc.update("IDAT".getBytes());
            bytePos = writeBytes( compressedLines, nCompressed, bytePos );
            crc.update( compressedLines, 0, nCompressed );

            crcValue = crc.getValue();
            bytePos = writeInt4( (int) crcValue, bytePos );
            scrunch.finish();
            return true;
        }
        catch (IOException e)
        {
            System.err.println( e.toString());
            return false;
        }
    }

    /**
     * Write a PNG "IEND" chunk into the pngBytes array.
     */
    protected void writeEnd()
    {
        bytePos = writeInt4( 0, bytePos );
        bytePos = writeString( "IEND", bytePos );
        crc.reset();
        crc.update("IEND".getBytes());
        crcValue = crc.getValue();
        bytePos = writeInt4( (int) crcValue, bytePos );
    }
}


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