Java tutorial
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); } } }