PngEncoder takes a Java Image object and creates a byte string which can be saved as a PNG file
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>david@catcode.com</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
* 15-Aug-2008 : Added scrunch.end() in writeImageData() method - see
* JFreeChart bug report 2037930 (David Gilbert);
*/
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};
/** PHYS tag. */
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.
*
* @return The image.
*/
public Image getImage() {
return this.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.
*
* @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) {
this.maxPos = Math.max(this.maxPos, offset + data.length);
if (data.length + offset > this.pngBytes.length) {
this.pngBytes = resizeByteArray(this.pngBytes, this.pngBytes.length
+ Math.max(1000, data.length));
}
System.arraycopy(data, 0, this.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) {
this.maxPos = Math.max(this.maxPos, offset + nBytes);
if (nBytes + offset > this.pngBytes.length) {
this.pngBytes = resizeByteArray(this.pngBytes, this.pngBytes.length
+ Math.max(1000, nBytes));
}
System.arraycopy(data, 0, this.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 b 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 PNG "IHDR" chunk into the pngBytes array.
*/
protected void writeHeader() {
int startPos = this.bytePos = writeInt4(13, this.bytePos);
this.bytePos = writeBytes(IHDR, this.bytePos);
this.width = this.image.getWidth(null);
this.height = this.image.getHeight(null);
this.bytePos = writeInt4(this.width, this.bytePos);
this.bytePos = writeInt4(this.height, this.bytePos);
this.bytePos = writeByte(8, this.bytePos); // bit depth
this.bytePos = writeByte((this.encodeAlpha) ? 6 : 2, this.bytePos);
// direct model
this.bytePos = writeByte(0, this.bytePos); // compression method
this.bytePos = writeByte(0, this.bytePos); // filter method
this.bytePos = writeByte(0, this.bytePos); // no interlace
this.crc.reset();
this.crc.update(this.pngBytes, startPos, this.bytePos - startPos);
this.crcValue = this.crc.getValue();
this.bytePos = writeInt4((int) this.crcValue, this.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 offset = this.bytesPerPixel;
int actualStart = startPos + offset;
int nBytes = width * this.bytesPerPixel;
int leftInsert = offset;
int leftExtract = 0;
for (int i = actualStart; i < startPos + nBytes; i++) {
this.leftBytes[leftInsert] = pixels[i];
pixels[i] = (byte) ((pixels[i] - this.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) {
final int nBytes = width * this.bytesPerPixel;
for (int i = 0; i < nBytes; i++) {
final byte currentByte = pixels[startPos + i];
pixels[startPos + i] = (byte) ((pixels[startPos + i]
- this.priorRow[i]) % 256);
this.priorRow[i] = currentByte;
}
}
/**
* 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 = this.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;
this.bytesPerPixel = (this.encodeAlpha) ? 4 : 3;
Deflater scrunch = new Deflater(this.compressionLevel);
ByteArrayOutputStream outBytes = new ByteArrayOutputStream(1024);
DeflaterOutputStream compBytes = new DeflaterOutputStream(outBytes,
scrunch);
try {
while (rowsLeft > 0) {
nRows = Math.min(32767 / (this.width
* (this.bytesPerPixel + 1)), rowsLeft);
nRows = Math.max(nRows, 1);
int[] pixels = new int[this.width * nRows];
pg = new PixelGrabber(this.image, 0, startRow,
this.width, nRows, pixels, 0, this.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[this.width * nRows * this.bytesPerPixel
+ nRows];
if (this.filter == FILTER_SUB) {
this.leftBytes = new byte[16];
}
if (this.filter == FILTER_UP) {
this.priorRow = new byte[this.width * this.bytesPerPixel];
}
scanPos = 0;
startPos = 1;
for (int i = 0; i < this.width * nRows; i++) {
if (i % this.width == 0) {
scanLines[scanPos++] = (byte) this.filter;
startPos = scanPos;
}
scanLines[scanPos++] = (byte) ((pixels[i] >> 16) & 0xff);
scanLines[scanPos++] = (byte) ((pixels[i] >> 8) & 0xff);
scanLines[scanPos++] = (byte) ((pixels[i]) & 0xff);
if (this.encodeAlpha) {
scanLines[scanPos++] = (byte) ((pixels[i] >> 24)
& 0xff);
}
if ((i % this.width == this.width - 1)
&& (this.filter != FILTER_NONE)) {
if (this.filter == FILTER_SUB) {
filterSub(scanLines, startPos, this.width);
}
if (this.filter == FILTER_UP) {
filterUp(scanLines, startPos, this.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;
this.crc.reset();
this.bytePos = writeInt4(nCompressed, this.bytePos);
this.bytePos = writeBytes(IDAT, this.bytePos);
this.crc.update(IDAT);
this.bytePos = writeBytes(compressedLines, nCompressed,
this.bytePos);
this.crc.update(compressedLines, 0, nCompressed);
this.crcValue = this.crc.getValue();
this.bytePos = writeInt4((int) this.crcValue, this.bytePos);
scrunch.finish();
scrunch.end();
return true;
}
catch (IOException e) {
System.err.println(e.toString());
return false;
}
}
/**
* Write a PNG "IEND" chunk into the pngBytes array.
*/
protected void writeEnd() {
this.bytePos = writeInt4(0, this.bytePos);
this.bytePos = writeBytes(IEND, this.bytePos);
this.crc.reset();
this.crc.update(IEND);
this.crcValue = this.crc.getValue();
this.bytePos = writeInt4((int) this.crcValue, this.bytePos);
}
/**
* Set the DPI for the X axis.
*
* @param xDpi The number of dots per inch
*/
public void setXDpi(int xDpi) {
this.xDpi = Math.round(xDpi / INCH_IN_METER_UNIT);
}
/**
* Get the DPI for the X axis.
*
* @return The number of dots per inch
*/
public int getXDpi() {
return Math.round(this.xDpi * INCH_IN_METER_UNIT);
}
/**
* Set the DPI for the Y axis.
*
* @param yDpi The number of dots per inch
*/
public void setYDpi(int yDpi) {
this.yDpi = Math.round(yDpi / INCH_IN_METER_UNIT);
}
/**
* Get the DPI for the Y axis.
*
* @return The number of dots per inch
*/
public int getYDpi() {
return Math.round(this.yDpi * INCH_IN_METER_UNIT);
}
/**
* Set the DPI resolution.
*
* @param xDpi The number of dots per inch for the X axis.
* @param yDpi The number of dots per inch for the Y axis.
*/
public void setDpi(int xDpi, int yDpi) {
this.xDpi = Math.round(xDpi / INCH_IN_METER_UNIT);
this.yDpi = Math.round(yDpi / INCH_IN_METER_UNIT);
}
/**
* Write a PNG "pHYs" chunk into the pngBytes array.
*/
protected void writeResolution() {
if (this.xDpi > 0 && this.yDpi > 0) {
final int startPos = this.bytePos = writeInt4(9, this.bytePos);
this.bytePos = writeBytes(PHYS, this.bytePos);
this.bytePos = writeInt4(this.xDpi, this.bytePos);
this.bytePos = writeInt4(this.yDpi, this.bytePos);
this.bytePos = writeByte(1, this.bytePos); // unit is the meter.
this.crc.reset();
this.crc.update(this.pngBytes, startPos, this.bytePos - startPos);
this.crcValue = this.crc.getValue();
this.bytePos = writeInt4((int) this.crcValue, this.bytePos);
}
}
}
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