将Javaimage对象转换成PNG格式字节数组

核心提示：/*** 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.** Than

　　/**
* 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.*;
import java.awt.image.*;
import java.util.*;
import java.util.zip.*;
import java.io.*;

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;

/**
* 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 };
int i;

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

/*
* 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;
}

/**
* 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 );
}

/**
* 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
{
while (rowsLeft > 0)
{
nRows = Math.min( 32767 / (width*(bytesPerPixel+1)), rowsLeft );
// nRows = rowsLeft;

int[] pixels = new int[width * nRows];

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 {
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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