    001package com.keypoint;
    002
    003import java.awt.Image;
    004import java.awt.image.ImageObserver;
    005import java.awt.image.PixelGrabber;
    006import java.io.ByteArrayOutputStream;
    007import java.io.IOException;
    008import java.util.zip.CRC32;
    009import java.util.zip.Deflater;
    010import java.util.zip.DeflaterOutputStream;
    011
    012/**
    013 * PngEncoder takes a Java Image object and creates a byte string which can be
    014 * saved as a PNG file.  The Image is presumed to use the DirectColorModel.
    015 *
    016 * <p>Thanks to Jay Denny at KeyPoint Software
    017 *    http://www.keypoint.com/
    018 * who let me develop this code on company time.</p>
    019 *
    020 * <p>You may contact me with (probably very-much-needed) improvements,
    021 * comments, and bug fixes at:</p>
    022 *
    023 *   <p><code>david@catcode.com</code></p>
    024 *
    025 * <p>This library is free software; you can redistribute it and/or
    026 * modify it under the terms of the GNU Lesser General Public
    027 * License as published by the Free Software Foundation; either
    028 * version 2.1 of the License, or (at your option) any later version.</p>
    029 *
    030 * <p>This library is distributed in the hope that it will be useful,
    031 * but WITHOUT ANY WARRANTY; without even the implied warranty of
    032 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    033 * Lesser General Public License for more details.</p>
    034 *
    035 * <p>You should have received a copy of the GNU Lesser General Public
    036 * License along with this library; if not, write to the Free Software
    037 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
    038 * USA. A copy of the GNU LGPL may be found at
    039 * <code>http://www.gnu.org/copyleft/lesser.html</code></p>
    040 *
    041 * @author J. David Eisenberg
    042 * @version 1.5, 19 Oct 2003
    043 *
    044 * CHANGES:
    045 * --------
    046 * 19-Nov-2002 : CODING STYLE CHANGES ONLY (by David Gilbert for Object
    047 *               Refinery Limited);
    048 * 19-Sep-2003 : Fix for platforms using EBCDIC (contributed by Paulo Soares);
    049 * 19-Oct-2003 : Change private fields to protected fields so that
    050 *               PngEncoderB can inherit them (JDE)
    051 *               Fixed bug with calculation of nRows
    052 * 15-Aug-2008 : Added scrunch.end() in writeImageData() method - see
    053 *               JFreeChart bug report 2037930 (David Gilbert);
    054 */
    055
    056public class PngEncoder {
    057
    058    /** Constant specifying that alpha channel should be encoded. */
    059    public static final boolean ENCODE_ALPHA = true;
    060
    061    /** Constant specifying that alpha channel should not be encoded. */
    062    public static final boolean NO_ALPHA = false;
    063
    064    /** Constants for filter (NONE). */
    065    public static final int FILTER_NONE = 0;
    066
    067    /** Constants for filter (SUB). */
    068    public static final int FILTER_SUB = 1;
    069
    070    /** Constants for filter (UP). */
    071    public static final int FILTER_UP = 2;
    072
    073    /** Constants for filter (LAST). */
    074    public static final int FILTER_LAST = 2;
    075
    076    /** IHDR tag. */
    077    protected static final byte[] IHDR = {73, 72, 68, 82};
    078
    079    /** IDAT tag. */
    080    protected static final byte[] IDAT = {73, 68, 65, 84};
    081
    082    /** IEND tag. */
    083    protected static final byte[] IEND = {73, 69, 78, 68};
    084
    085    /** PHYS tag. */
    086    protected static final byte[] PHYS = {(byte)'p', (byte)'H', (byte)'Y',
    087        (byte)'s'};
    088
    089    /** The png bytes. */
    090    protected byte[] pngBytes;
    091
    092    /** The prior row. */
    093    protected byte[] priorRow;
    094
    095    /** The left bytes. */
    096    protected byte[] leftBytes;
    097
    098    /** The image. */
    099    protected Image image;
    100
    101    /** The width. */
    102    protected int width;
    103
    104    /** The height. */
    105    protected int height;
    106
    107    /** The byte position. */
    108    protected int bytePos;
    109
    110    /** The maximum position. */
    111    protected int maxPos;
    112
    113    /** CRC. */
    114    protected CRC32 crc = new CRC32();
    115
    116    /** The CRC value. */
    117    protected long crcValue;
    118
    119    /** Encode alpha? */
    120    protected boolean encodeAlpha;
    121
    122    /** The filter type. */
    123    protected int filter;
    124
    125    /** The bytes-per-pixel. */
    126    protected int bytesPerPixel;
    127
    128    /** The physical pixel dimension : number of pixels per inch on the X axis. */
    129    private int xDpi = 0;
    130
    131    /** The physical pixel dimension : number of pixels per inch on the Y axis. */
    132    private int yDpi = 0;
    133
    134    /** Used for conversion of DPI to Pixels per Meter. */
    135    static private float INCH_IN_METER_UNIT = 0.0254f;
    136
    137    /**
    138     * The compression level (1 = best speed, 9 = best compression,
    139     * 0 = no compression).
    140     */
    141    protected int compressionLevel;
    142
    143    /**
    144     * Class constructor.
    145     */
    146    public PngEncoder() {
    147        this(null, false, FILTER_NONE, 0);
    148    }
    149
    150    /**
    151     * Class constructor specifying Image to encode, with no alpha channel
    152     * encoding.
    153     *
    154     * @param image A Java Image object which uses the DirectColorModel
    155     * @see java.awt.Image
    156     */
    157    public PngEncoder(Image image) {
    158        this(image, false, FILTER_NONE, 0);
    159    }
    160
    161    /**
    162     * Class constructor specifying Image to encode, and whether to encode
    163     * alpha.
    164     *
    165     * @param image A Java Image object which uses the DirectColorModel
    166     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
    167     * @see java.awt.Image
    168     */
    169    public PngEncoder(Image image, boolean encodeAlpha) {
    170        this(image, encodeAlpha, FILTER_NONE, 0);
    171    }
    172
    173    /**
    174     * Class constructor specifying Image to encode, whether to encode alpha,
    175     * and filter to use.
    176     *
    177     * @param image A Java Image object which uses the DirectColorModel
    178     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
    179     * @param whichFilter 0=none, 1=sub, 2=up
    180     * @see java.awt.Image
    181     */
    182    public PngEncoder(Image image, boolean encodeAlpha, int whichFilter) {
    183        this(image, encodeAlpha, whichFilter, 0);
    184    }
    185
    186
    187    /**
    188     * Class constructor specifying Image source to encode, whether to encode
    189     * alpha, filter to use, and compression level.
    190     *
    191     * @param image A Java Image object
    192     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
    193     * @param whichFilter 0=none, 1=sub, 2=up
    194     * @param compLevel 0..9 (1 = best speed, 9 = best compression, 0 = no
    195     *        compression)
    196     * @see java.awt.Image
    197     */
    198    public PngEncoder(Image image, boolean encodeAlpha, int whichFilter,
    199            int compLevel) {
    200        this.image = image;
    201        this.encodeAlpha = encodeAlpha;
    202        setFilter(whichFilter);
    203        if (compLevel >= 0 && compLevel <= 9) {
    204            this.compressionLevel = compLevel;
    205        }
    206    }
    207
    208    /**
    209     * Set the image to be encoded.
    210     *
    211     * @param image A Java Image object which uses the DirectColorModel
    212     * @see java.awt.Image
    213     * @see java.awt.image.DirectColorModel
    214     */
    215    public void setImage(Image image) {
    216        this.image = image;
    217        this.pngBytes = null;
    218    }
    219
    220    /**
    221     * Returns the image to be encoded.
    222     *
    223     * @return The image.
    224     */
    225    public Image getImage() {
    226      return this.image;
    227    }
    228
    229  /**
    230     * Creates an array of bytes that is the PNG equivalent of the current
    231     * image, specifying whether to encode alpha or not.
    232     *
    233     * @param encodeAlpha boolean false=no alpha, true=encode alpha
    234     * @return an array of bytes, or null if there was a problem
    235     */
    236    public byte[] pngEncode(boolean encodeAlpha) {
    237        byte[]  pngIdBytes = {-119, 80, 78, 71, 13, 10, 26, 10};
    238
    239        if (this.image == null) {
    240            return null;
    241        }
    242        this.width = this.image.getWidth(null);
    243        this.height = this.image.getHeight(null);
    244
    245        /*
    246         * start with an array that is big enough to hold all the pixels
    247         * (plus filter bytes), and an extra 200 bytes for header info
    248         */
    249        this.pngBytes = new byte[((this.width + 1) * this.height * 3) + 200];
    250
    251        /*
    252         * keep track of largest byte written to the array
    253         */
    254        this.maxPos = 0;
    255
    256        this.bytePos = writeBytes(pngIdBytes, 0);
    257        //hdrPos = bytePos;
    258        writeHeader();
    259        writeResolution();
    260        //dataPos = bytePos;
    261        if (writeImageData()) {
    262            writeEnd();
    263            this.pngBytes = resizeByteArray(this.pngBytes, this.maxPos);
    264        }
    265        else {
    266            this.pngBytes = null;
    267        }
    268        return this.pngBytes;
    269    }
    270
    271    /**
    272     * Creates an array of bytes that is the PNG equivalent of the current
    273     * image.  Alpha encoding is determined by its setting in the constructor.
    274     *
    275     * @return an array of bytes, or null if there was a problem
    276     */
    277    public byte[] pngEncode() {
    278        return pngEncode(this.encodeAlpha);
    279    }
    280
    281    /**
    282     * Set the alpha encoding on or off.
    283     *
    284     * @param encodeAlpha  false=no, true=yes
    285     */
    286    public void setEncodeAlpha(boolean encodeAlpha) {
    287        this.encodeAlpha = encodeAlpha;
    288    }
    289
    290    /**
    291     * Retrieve alpha encoding status.
    292     *
    293     * @return boolean false=no, true=yes
    294     */
    295    public boolean getEncodeAlpha() {
    296        return this.encodeAlpha;
    297    }
    298
    299    /**
    300     * Set the filter to use.
    301     *
    302     * @param whichFilter from constant list
    303     */
    304    public void setFilter(int whichFilter) {
    305        this.filter = FILTER_NONE;
    306        if (whichFilter <= FILTER_LAST) {
    307            this.filter = whichFilter;
    308        }
    309    }
    310
    311    /**
    312     * Retrieve filtering scheme.
    313     *
    314     * @return int (see constant list)
    315     */
    316    public int getFilter() {
    317        return this.filter;
    318    }
    319
    320    /**
    321     * Set the compression level to use.
    322     *
    323     * @param level the compression level (1 = best speed, 9 = best compression,
    324     *        0 = no compression)
    325     */
    326    public void setCompressionLevel(int level) {
    327        if (level >= 0 && level <= 9) {
    328            this.compressionLevel = level;
    329        }
    330    }
    331
    332    /**
    333     * Retrieve compression level.
    334     *
    335     * @return int (1 = best speed, 9 = best compression, 0 = no compression)
    336     */
    337    public int getCompressionLevel() {
    338        return this.compressionLevel;
    339    }
    340
    341    /**
    342     * Increase or decrease the length of a byte array.
    343     *
    344     * @param array The original array.
    345     * @param newLength The length you wish the new array to have.
    346     * @return Array of newly desired length. If shorter than the
    347     *         original, the trailing elements are truncated.
    348     */
    349    protected byte[] resizeByteArray(byte[] array, int newLength) {
    350        byte[]  newArray = new byte[newLength];
    351        int     oldLength = array.length;
    352
    353        System.arraycopy(array, 0, newArray, 0, Math.min(oldLength, newLength));
    354        return newArray;
    355    }
    356
    357    /**
    358     * Write an array of bytes into the pngBytes array.
    359     * Note: This routine has the side effect of updating
    360     * maxPos, the largest element written in the array.
    361     * The array is resized by 1000 bytes or the length
    362     * of the data to be written, whichever is larger.
    363     *
    364     * @param data The data to be written into pngBytes.
    365     * @param offset The starting point to write to.
    366     * @return The next place to be written to in the pngBytes array.
    367     */
    368    protected int writeBytes(byte[] data, int offset) {
    369        this.maxPos = Math.max(this.maxPos, offset + data.length);
    370        if (data.length + offset > this.pngBytes.length) {
    371            this.pngBytes = resizeByteArray(this.pngBytes, this.pngBytes.length
    372                    + Math.max(1000, data.length));
    373        }
    374        System.arraycopy(data, 0, this.pngBytes, offset, data.length);
    375        return offset + data.length;
    376    }
    377
    378    /**
    379     * Write an array of bytes into the pngBytes array, specifying number of
    380     * bytes to write. Note: This routine has the side effect of updating
    381     * maxPos, the largest element written in the array.
    382     * The array is resized by 1000 bytes or the length
    383     * of the data to be written, whichever is larger.
    384     *
    385     * @param data The data to be written into pngBytes.
    386     * @param nBytes The number of bytes to be written.
    387     * @param offset The starting point to write to.
    388     * @return The next place to be written to in the pngBytes array.
    389     */
    390    protected int writeBytes(byte[] data, int nBytes, int offset) {
    391        this.maxPos = Math.max(this.maxPos, offset + nBytes);
    392        if (nBytes + offset > this.pngBytes.length) {
    393            this.pngBytes = resizeByteArray(this.pngBytes, this.pngBytes.length
    394                    + Math.max(1000, nBytes));
    395        }
    396        System.arraycopy(data, 0, this.pngBytes, offset, nBytes);
    397        return offset + nBytes;
    398    }
    399
    400    /**
    401     * Write a two-byte integer into the pngBytes array at a given position.
    402     *
    403     * @param n The integer to be written into pngBytes.
    404     * @param offset The starting point to write to.
    405     * @return The next place to be written to in the pngBytes array.
    406     */
    407    protected int writeInt2(int n, int offset) {
    408        byte[] temp = {(byte) ((n >> 8) & 0xff), (byte) (n & 0xff)};
    409        return writeBytes(temp, offset);
    410    }
    411
    412    /**
    413     * Write a four-byte integer into the pngBytes array at a given position.
    414     *
    415     * @param n The integer to be written into pngBytes.
    416     * @param offset The starting point to write to.
    417     * @return The next place to be written to in the pngBytes array.
    418     */
    419    protected int writeInt4(int n, int offset) {
    420        byte[] temp = {(byte) ((n >> 24) & 0xff),
    421                       (byte) ((n >> 16) & 0xff),
    422                       (byte) ((n >> 8) & 0xff),
    423                       (byte) (n & 0xff)};
    424        return writeBytes(temp, offset);
    425    }
    426
    427    /**
    428     * Write a single byte into the pngBytes array at a given position.
    429     *
    430     * @param b The integer to be written into pngBytes.
    431     * @param offset The starting point to write to.
    432     * @return The next place to be written to in the pngBytes array.
    433     */
    434    protected int writeByte(int b, int offset) {
    435        byte[] temp = {(byte) b};
    436        return writeBytes(temp, offset);
    437    }
    438
    439    /**
    440     * Write a PNG "IHDR" chunk into the pngBytes array.
    441     */
    442    protected void writeHeader() {
    443
    444        int startPos = this.bytePos = writeInt4(13, this.bytePos);
    445        this.bytePos = writeBytes(IHDR, this.bytePos);
    446        this.width = this.image.getWidth(null);
    447        this.height = this.image.getHeight(null);
    448        this.bytePos = writeInt4(this.width, this.bytePos);
    449        this.bytePos = writeInt4(this.height, this.bytePos);
    450        this.bytePos = writeByte(8, this.bytePos); // bit depth
    451        this.bytePos = writeByte((this.encodeAlpha) ? 6 : 2, this.bytePos);
    452            // direct model
    453        this.bytePos = writeByte(0, this.bytePos); // compression method
    454        this.bytePos = writeByte(0, this.bytePos); // filter method
    455        this.bytePos = writeByte(0, this.bytePos); // no interlace
    456        this.crc.reset();
    457        this.crc.update(this.pngBytes, startPos, this.bytePos - startPos);
    458        this.crcValue = this.crc.getValue();
    459        this.bytePos = writeInt4((int) this.crcValue, this.bytePos);
    460    }
    461
    462    /**
    463     * Perform "sub" filtering on the given row.
    464     * Uses temporary array leftBytes to store the original values
    465     * of the previous pixels.  The array is 16 bytes long, which
    466     * will easily hold two-byte samples plus two-byte alpha.
    467     *
    468     * @param pixels The array holding the scan lines being built
    469     * @param startPos Starting position within pixels of bytes to be filtered.
    470     * @param width Width of a scanline in pixels.
    471     */
    472    protected void filterSub(byte[] pixels, int startPos, int width) {
    473        int offset = this.bytesPerPixel;
    474        int actualStart = startPos + offset;
    475        int nBytes = width * this.bytesPerPixel;
    476        int leftInsert = offset;
    477        int leftExtract = 0;
    478
    479        for (int i = actualStart; i < startPos + nBytes; i++) {
    480            this.leftBytes[leftInsert] =  pixels[i];
    481            pixels[i] = (byte) ((pixels[i] - this.leftBytes[leftExtract])
    482                     % 256);
    483            leftInsert = (leftInsert + 1) % 0x0f;
    484            leftExtract = (leftExtract + 1) % 0x0f;
    485        }
    486    }
    487
    488    /**
    489     * Perform "up" filtering on the given row.
    490     * Side effect: refills the prior row with current row
    491     *
    492     * @param pixels The array holding the scan lines being built
    493     * @param startPos Starting position within pixels of bytes to be filtered.
    494     * @param width Width of a scanline in pixels.
    495     */
    496    protected void filterUp(byte[] pixels, int startPos, int width) {
    497
    498        final int nBytes = width * this.bytesPerPixel;
    499
    500        for (int i = 0; i < nBytes; i++) {
    501            final byte currentByte = pixels[startPos + i];
    502            pixels[startPos + i] = (byte) ((pixels[startPos  + i]
    503                    - this.priorRow[i]) % 256);
    504            this.priorRow[i] = currentByte;
    505        }
    506    }
    507
    508    /**
    509     * Write the image data into the pngBytes array.
    510     * This will write one or more PNG "IDAT" chunks. In order
    511     * to conserve memory, this method grabs as many rows as will
    512     * fit into 32K bytes, or the whole image; whichever is less.
    513     *
    514     *
    515     * @return true if no errors; false if error grabbing pixels
    516     */
    517    protected boolean writeImageData() {
    518        int rowsLeft = this.height;  // number of rows remaining to write
    519        int startRow = 0;       // starting row to process this time through
    520        int nRows;              // how many rows to grab at a time
    521
    522        byte[] scanLines;       // the scan lines to be compressed
    523        int scanPos;            // where we are in the scan lines
    524        int startPos;           // where this line's actual pixels start (used
    525                                // for filtering)
    526
    527        byte[] compressedLines; // the resultant compressed lines
    528        int nCompressed;        // how big is the compressed area?
    529
    530        //int depth;              // color depth ( handle only 8 or 32 )
    531
    532        PixelGrabber pg;
    533
    534        this.bytesPerPixel = (this.encodeAlpha) ? 4 : 3;
    535
    536        Deflater scrunch = new Deflater(this.compressionLevel);
    537        ByteArrayOutputStream outBytes = new ByteArrayOutputStream(1024);
    538
    539        DeflaterOutputStream compBytes = new DeflaterOutputStream(outBytes,
    540                scrunch);
    541        try {
    542            while (rowsLeft > 0) {
    543                nRows = Math.min(32767 / (this.width
    544                        * (this.bytesPerPixel + 1)), rowsLeft);
    545                nRows = Math.max(nRows, 1);
    546
    547                int[] pixels = new int[this.width * nRows];
    548
    549                pg = new PixelGrabber(this.image, 0, startRow,
    550                        this.width, nRows, pixels, 0, this.width);
    551                try {
    552                    pg.grabPixels();
    553                }
    554                catch (Exception e) {
    555                    System.err.println("interrupted waiting for pixels!");
    556                    return false;
    557                }
    558                if ((pg.getStatus() & ImageObserver.ABORT) != 0) {
    559                    System.err.println("image fetch aborted or errored");
    560                    return false;
    561                }
    562
    563                /*
    564                 * Create a data chunk. scanLines adds "nRows" for
    565                 * the filter bytes.
    566                 */
    567                scanLines = new byte[this.width * nRows * this.bytesPerPixel
    568                                     + nRows];
    569
    570                if (this.filter == FILTER_SUB) {
    571                    this.leftBytes = new byte[16];
    572                }
    573                if (this.filter == FILTER_UP) {
    574                    this.priorRow = new byte[this.width * this.bytesPerPixel];
    575                }
    576
    577                scanPos = 0;
    578                startPos = 1;
    579                for (int i = 0; i < this.width * nRows; i++) {
    580                    if (i % this.width == 0) {
    581                        scanLines[scanPos++] = (byte) this.filter;
    582                        startPos = scanPos;
    583                    }
    584                    scanLines[scanPos++] = (byte) ((pixels[i] >> 16) & 0xff);
    585                    scanLines[scanPos++] = (byte) ((pixels[i] >>  8) & 0xff);
    586                    scanLines[scanPos++] = (byte) ((pixels[i]) & 0xff);
    587                    if (this.encodeAlpha) {
    588                        scanLines[scanPos++] = (byte) ((pixels[i] >> 24)
    589                                & 0xff);
    590                    }
    591                    if ((i % this.width == this.width - 1)
    592                            && (this.filter != FILTER_NONE)) {
    593                        if (this.filter == FILTER_SUB) {
    594                            filterSub(scanLines, startPos, this.width);
    595                        }
    596                        if (this.filter == FILTER_UP) {
    597                            filterUp(scanLines, startPos, this.width);
    598                        }
    599                    }
    600                }
    601
    602                /*
    603                 * Write these lines to the output area
    604                 */
    605                compBytes.write(scanLines, 0, scanPos);
    606
    607                startRow += nRows;
    608                rowsLeft -= nRows;
    609            }
    610            compBytes.close();
    611
    612            /*
    613             * Write the compressed bytes
    614             */
    615            compressedLines = outBytes.toByteArray();
    616            nCompressed = compressedLines.length;
    617
    618            this.crc.reset();
    619            this.bytePos = writeInt4(nCompressed, this.bytePos);
    620            this.bytePos = writeBytes(IDAT, this.bytePos);
    621            this.crc.update(IDAT);
    622            this.bytePos = writeBytes(compressedLines, nCompressed,
    623                    this.bytePos);
    624            this.crc.update(compressedLines, 0, nCompressed);
    625
    626            this.crcValue = this.crc.getValue();
    627            this.bytePos = writeInt4((int) this.crcValue, this.bytePos);
    628            scrunch.finish();
    629            scrunch.end();
    630            return true;
    631        }
    632        catch (IOException e) {
    633            System.err.println(e.toString());
    634            return false;
    635        }
    636    }
    637
    638    /**
    639     * Write a PNG "IEND" chunk into the pngBytes array.
    640     */
    641    protected void writeEnd() {
    642        this.bytePos = writeInt4(0, this.bytePos);
    643        this.bytePos = writeBytes(IEND, this.bytePos);
    644        this.crc.reset();
    645        this.crc.update(IEND);
    646        this.crcValue = this.crc.getValue();
    647        this.bytePos = writeInt4((int) this.crcValue, this.bytePos);
    648    }
    649
    650
    651    /**
    652     * Set the DPI for the X axis.
    653     *
    654     * @param xDpi  The number of dots per inch
    655     */
    656    public void setXDpi(int xDpi) {
    657        this.xDpi = Math.round(xDpi / INCH_IN_METER_UNIT);
    658
    659    }
    660
    661    /**
    662     * Get the DPI for the X axis.
    663     *
    664     * @return The number of dots per inch
    665     */
    666    public int getXDpi() {
    667        return Math.round(this.xDpi * INCH_IN_METER_UNIT);
    668    }
    669
    670    /**
    671     * Set the DPI for the Y axis.
    672     *
    673     * @param yDpi  The number of dots per inch
    674     */
    675    public void setYDpi(int yDpi) {
    676        this.yDpi = Math.round(yDpi / INCH_IN_METER_UNIT);
    677    }
    678
    679    /**
    680     * Get the DPI for the Y axis.
    681     *
    682     * @return The number of dots per inch
    683     */
    684    public int getYDpi() {
    685        return Math.round(this.yDpi * INCH_IN_METER_UNIT);
    686    }
    687
    688    /**
    689     * Set the DPI resolution.
    690     *
    691     * @param xDpi  The number of dots per inch for the X axis.
    692     * @param yDpi  The number of dots per inch for the Y axis.
    693     */
    694    public void setDpi(int xDpi, int yDpi) {
    695        this.xDpi = Math.round(xDpi / INCH_IN_METER_UNIT);
    696        this.yDpi = Math.round(yDpi / INCH_IN_METER_UNIT);
    697    }
    698
    699    /**
    700     * Write a PNG "pHYs" chunk into the pngBytes array.
    701     */
    702    protected void writeResolution() {
    703        if (this.xDpi > 0 && this.yDpi > 0) {
    704
    705            final int startPos = this.bytePos = writeInt4(9, this.bytePos);
    706            this.bytePos = writeBytes(PHYS, this.bytePos);
    707            this.bytePos = writeInt4(this.xDpi, this.bytePos);
    708            this.bytePos = writeInt4(this.yDpi, this.bytePos);
    709            this.bytePos = writeByte(1, this.bytePos); // unit is the meter.
    710
    711            this.crc.reset();
    712            this.crc.update(this.pngBytes, startPos, this.bytePos - startPos);
    713            this.crcValue = this.crc.getValue();
    714            this.bytePos = writeInt4((int) this.crcValue, this.bytePos);
    715        }
    716    }
    717}