Class PngEncoder

java.lang.Object
com.keypoint.PngEncoder
public class PngEncoder extends Object
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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. A copy of the GNU LGPL may be found at http://www.gnu.org/copyleft/lesser.html

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);
Author:
J. David Eisenberg

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    protected int
    bytePos
    The byte position.
    protected int
    bytesPerPixel
    The bytes-per-pixel.
    protected int
    compressionLevel
    The compression level (1 = best speed, 9 = best compression, 0 = no compression).
    protected CRC32
    crc
    CRC.
    protected long
    crcValue
    The CRC value.
    static final boolean
    ENCODE_ALPHA
    Constant specifying that alpha channel should be encoded.
    protected boolean
    encodeAlpha
    Encode alpha?
    protected int
    filter
    The filter type.
    static final int
    FILTER_LAST
    Constants for filter (LAST).
    static final int
    FILTER_NONE
    Constants for filter (NONE).
    static final int
    FILTER_SUB
    Constants for filter (SUB).
    static final int
    FILTER_UP
    Constants for filter (UP).
    protected int
    height
    The height.
    protected static final byte[]
    IDAT
    IDAT tag.
    protected static final byte[]
    IEND
    IEND tag.
    protected static final byte[]
    IHDR
    IHDR tag.
    protected Image
    image
    The image.
    protected byte[]
    leftBytes
    The left bytes.
    protected int
    maxPos
    The maximum position.
    static final boolean
    NO_ALPHA
    Constant specifying that alpha channel should not be encoded.
    protected static final byte[]
    PHYS
    PHYS tag.
    protected byte[]
    pngBytes
    The png bytes.
    protected byte[]
    priorRow
    The prior row.
    protected int
    width
    The width.

  • Constructor Summary

    Constructors
    Constructor
    Description
    PngEncoder()
    Class constructor.
    PngEncoder(Image image)
    Class constructor specifying Image to encode, with no alpha channel encoding.
    PngEncoder(Image image, boolean encodeAlpha)
    Class constructor specifying Image to encode, and whether to encode alpha.
    PngEncoder(Image image, boolean encodeAlpha, int whichFilter)
    Class constructor specifying Image to encode, whether to encode alpha, and filter to use.
    PngEncoder(Image image, boolean encodeAlpha, int whichFilter, int compLevel)
    Class constructor specifying Image source to encode, whether to encode alpha, filter to use, and compression level.

  • Method Summary

    Modifier and Type
    Method
    Description
    protected void
    filterSub(byte[] pixels, int startPos, int width)
    Perform "sub" filtering on the given row.
    protected void
    filterUp(byte[] pixels, int startPos, int width)
    Perform "up" filtering on the given row.
    int
    getCompressionLevel()
    Retrieve compression level.
    boolean
    getEncodeAlpha()
    Retrieve alpha encoding status.
    int
    getFilter()
    Retrieve filtering scheme.
    Image
    getImage()
    Returns the image to be encoded.
    int
    getXDpi()
    Get the DPI for the X axis.
    int
    getYDpi()
    Get the DPI for the Y axis.
    byte[]
    pngEncode()
    Creates an array of bytes that is the PNG equivalent of the current image.
    byte[]
    pngEncode(boolean encodeAlpha)
    Creates an array of bytes that is the PNG equivalent of the current image, specifying whether to encode alpha or not.
    protected byte[]
    resizeByteArray(byte[] array, int newLength)
    Increase or decrease the length of a byte array.
    void
    setCompressionLevel(int level)
    Set the compression level to use.
    void
    setDpi(int xDpi, int yDpi)
    Set the DPI resolution.
    void
    setEncodeAlpha(boolean encodeAlpha)
    Set the alpha encoding on or off.
    void
    setFilter(int whichFilter)
    Set the filter to use.
    void
    setImage(Image image)
    Set the image to be encoded.
    void
    setXDpi(int xDpi)
    Set the DPI for the X axis.
    void
    setYDpi(int yDpi)
    Set the DPI for the Y axis.
    protected int
    writeByte(int b, int offset)
    Write a single byte into the pngBytes array at a given position.
    protected int
    writeBytes(byte[] data, int offset)
    Write an array of bytes into the pngBytes array.
    protected int
    writeBytes(byte[] data, int nBytes, int offset)
    Write an array of bytes into the pngBytes array, specifying number of bytes to write.
    protected void
    writeEnd()
    Write a PNG "IEND" chunk into the pngBytes array.
    protected void
    writeHeader()
    Write a PNG "IHDR" chunk into the pngBytes array.
    protected boolean
    writeImageData()
    Write the image data into the pngBytes array.
    protected int
    writeInt2(int n, int offset)
    Write a two-byte integer into the pngBytes array at a given position.
    protected int
    writeInt4(int n, int offset)
    Write a four-byte integer into the pngBytes array at a given position.
    protected void
    writeResolution()
    Write a PNG "pHYs" chunk into the pngBytes array.

    Methods inherited from class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • ENCODE_ALPHA

      public static final boolean ENCODE_ALPHA
      Constant specifying that alpha channel should be encoded.
      See Also:

    • NO_ALPHA

      public static final boolean NO_ALPHA
      Constant specifying that alpha channel should not be encoded.
      See Also:

    • FILTER_NONE

      public static final int FILTER_NONE
      Constants for filter (NONE).
      See Also:

    • FILTER_SUB

      public static final int FILTER_SUB
      Constants for filter (SUB).
      See Also:

    • FILTER_UP

      public static final int FILTER_UP
      Constants for filter (UP).
      See Also:

    • FILTER_LAST

      public static final int FILTER_LAST
      Constants for filter (LAST).
      See Also:

    • IHDR

      protected static final byte[] IHDR
      IHDR tag.

    • IDAT

      protected static final byte[] IDAT
      IDAT tag.

    • IEND

      protected static final byte[] IEND
      IEND tag.

    • PHYS

      protected static final byte[] PHYS
      PHYS tag.

    • pngBytes

      protected byte[] pngBytes
      The png bytes.

    • priorRow

      protected byte[] priorRow
      The prior row.

    • leftBytes

      protected byte[] leftBytes
      The left bytes.

    • image

      protected Image image
      The image.

    • width

      protected int width
      The width.

    • height

      protected int height
      The height.

    • bytePos

      protected int bytePos
      The byte position.

    • maxPos

      protected int maxPos
      The maximum position.

    • crc

      protected CRC32 crc
      CRC.

    • crcValue

      protected long crcValue
      The CRC value.

    • encodeAlpha

      protected boolean encodeAlpha
      Encode alpha?

    • filter

      protected int filter
      The filter type.

    • bytesPerPixel

      protected int bytesPerPixel
      The bytes-per-pixel.

    • compressionLevel

      protected int compressionLevel
      The compression level (1 = best speed, 9 = best compression, 0 = no compression).

  • Constructor Details

    • PngEncoder

      public PngEncoder()
      Class constructor.

    • PngEncoder

      public PngEncoder(Image image)
      Class constructor specifying Image to encode, with no alpha channel encoding.
      Parameters:
      image - A Java Image object which uses the DirectColorModel
      See Also:

    • PngEncoder

      public PngEncoder(Image image, boolean encodeAlpha)
      Class constructor specifying Image to encode, and whether to encode alpha.
      Parameters:
      image - A Java Image object which uses the DirectColorModel
      encodeAlpha - Encode the alpha channel? false=no; true=yes
      See Also:

    • PngEncoder

      public PngEncoder(Image image, boolean encodeAlpha, int whichFilter)
      Class constructor specifying Image to encode, whether to encode alpha, and filter to use.
      Parameters:
      image - A Java Image object which uses the DirectColorModel
      encodeAlpha - Encode the alpha channel? false=no; true=yes
      whichFilter - 0=none, 1=sub, 2=up
      See Also:

    • PngEncoder

      public PngEncoder(Image image, boolean encodeAlpha, int whichFilter, int compLevel)
      Class constructor specifying Image source to encode, whether to encode alpha, filter to use, and compression level.
      Parameters:
      image - A Java Image object
      encodeAlpha - Encode the alpha channel? false=no; true=yes
      whichFilter - 0=none, 1=sub, 2=up
      compLevel - 0..9 (1 = best speed, 9 = best compression, 0 = no compression)
      See Also:

  • Method Details

    • setImage

      public void setImage(Image image)
      Set the image to be encoded.
      Parameters:
      image - A Java Image object which uses the DirectColorModel
      See Also:

    • getImage

      public Image getImage()
      Returns the image to be encoded.
      Returns:
      The image.

    • pngEncode

      public byte[] pngEncode(boolean encodeAlpha)
      Creates an array of bytes that is the PNG equivalent of the current image, specifying whether to encode alpha or not.
      Parameters:
      encodeAlpha - boolean false=no alpha, true=encode alpha
      Returns:
      an array of bytes, or null if there was a problem

    • pngEncode

      public byte[] pngEncode()
      Creates an array of bytes that is the PNG equivalent of the current image. Alpha encoding is determined by its setting in the constructor.
      Returns:
      an array of bytes, or null if there was a problem

    • setEncodeAlpha

      public void setEncodeAlpha(boolean encodeAlpha)
      Set the alpha encoding on or off.
      Parameters:
      encodeAlpha - false=no, true=yes

    • getEncodeAlpha

      public boolean getEncodeAlpha()
      Retrieve alpha encoding status.
      Returns:
      boolean false=no, true=yes

    • setFilter

      public void setFilter(int whichFilter)
      Set the filter to use.
      Parameters:
      whichFilter - from constant list

    • getFilter

      public int getFilter()
      Retrieve filtering scheme.
      Returns:
      int (see constant list)

    • setCompressionLevel

      public void setCompressionLevel(int level)
      Set the compression level to use.
      Parameters:
      level - the compression level (1 = best speed, 9 = best compression, 0 = no compression)

    • getCompressionLevel

      public int getCompressionLevel()
      Retrieve compression level.
      Returns:
      int (1 = best speed, 9 = best compression, 0 = no compression)

    • resizeByteArray

      protected byte[] resizeByteArray(byte[] array, int newLength)
      Increase or decrease the length of a byte array.
      Parameters:
      array - The original array.
      newLength - The length you wish the new array to have.
      Returns:
      Array of newly desired length. If shorter than the original, the trailing elements are truncated.

    • writeBytes

      protected int writeBytes(byte[] data, int offset)
      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.
      Parameters:
      data - The data to be written into pngBytes.
      offset - The starting point to write to.
      Returns:
      The next place to be written to in the pngBytes array.

    • writeBytes

      protected int writeBytes(byte[] data, int nBytes, int offset)
      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.
      Parameters:
      data - The data to be written into pngBytes.
      nBytes - The number of bytes to be written.
      offset - The starting point to write to.
      Returns:
      The next place to be written to in the pngBytes array.

    • writeInt2

      protected int writeInt2(int n, int offset)
      Write a two-byte integer into the pngBytes array at a given position.
      Parameters:
      n - The integer to be written into pngBytes.
      offset - The starting point to write to.
      Returns:
      The next place to be written to in the pngBytes array.

    • writeInt4

      protected int writeInt4(int n, int offset)
      Write a four-byte integer into the pngBytes array at a given position.
      Parameters:
      n - The integer to be written into pngBytes.
      offset - The starting point to write to.
      Returns:
      The next place to be written to in the pngBytes array.

    • writeByte

      protected int writeByte(int b, int offset)
      Write a single byte into the pngBytes array at a given position.
      Parameters:
      b - The integer to be written into pngBytes.
      offset - The starting point to write to.
      Returns:
      The next place to be written to in the pngBytes array.

    • writeHeader

      protected void writeHeader()
      Write a PNG "IHDR" chunk into the pngBytes array.

    • filterSub

      protected void filterSub(byte[] pixels, int startPos, int width)
      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.
      Parameters:
      pixels - The array holding the scan lines being built
      startPos - Starting position within pixels of bytes to be filtered.
      width - Width of a scanline in pixels.

    • filterUp

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

    • writeImageData

      protected boolean writeImageData()
      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.
      Returns:
      true if no errors; false if error grabbing pixels

    • writeEnd

      protected void writeEnd()
      Write a PNG "IEND" chunk into the pngBytes array.

    • setXDpi

      public void setXDpi(int xDpi)
      Set the DPI for the X axis.
      Parameters:
      xDpi - The number of dots per inch

    • getXDpi

      public int getXDpi()
      Get the DPI for the X axis.
      Returns:
      The number of dots per inch

    • setYDpi

      public void setYDpi(int yDpi)
      Set the DPI for the Y axis.
      Parameters:
      yDpi - The number of dots per inch

    • getYDpi

      public int getYDpi()
      Get the DPI for the Y axis.
      Returns:
      The number of dots per inch

    • setDpi

      public void setDpi(int xDpi, int yDpi)
      Set the DPI resolution.
      Parameters:
      xDpi - The number of dots per inch for the X axis.
      yDpi - The number of dots per inch for the Y axis.

    • writeResolution

      protected void writeResolution()
      Write a PNG "pHYs" chunk into the pngBytes array.