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## com.keypoint
Class PngEncoder

    java.lang.Object
      com.keypoint.PngEncoder

    public class PngEncoder

extends java.lang.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
`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 java.util.zip.CRC32` | `crc` CRC.
`protected long` | `crcValue` The CRC value.
`static boolean` | `ENCODE_ALPHA` Constant specifying that alpha channel should be encoded.
`protected boolean` | `encodeAlpha` Encode alpha?
`protected int` | `filter` The filter type.
`static int` | `FILTER_LAST` Constants for filter (LAST).
`static int` | `FILTER_NONE` Constants for filter (NONE).
`static int` | `FILTER_SUB` Constants for filter (SUB).
`static int` | `FILTER_UP` Constants for filter (UP).
`protected int` | `height` The height.
`protected static byte[]` | `IDAT` IDAT tag.
`protected static byte[]` | `IEND` IEND tag.
`protected static byte[]` | `IHDR` IHDR tag.
`protected java.awt.Image` | `image` The image.
`protected byte[]` | `leftBytes` The left bytes.
`protected int` | `maxPos` The maximum position.
`static boolean` | `NO_ALPHA` Constant specifying that alpha channel should not be encoded.
`protected static byte[]` | `PHYS` PHYS tag.
`protected byte[]` | `pngBytes` The png bytes.
`protected byte[]` | `priorRow` The prior row.
`protected int` | `width` The width.

Constructor Summary
`PngEncoder()` Class constructor.
`PngEncoder(java.awt.Image image)` Class constructor specifying Image to encode, with no alpha channel encoding.
`PngEncoder(java.awt.Image image, boolean encodeAlpha)` Class constructor specifying Image to encode, and whether to encode alpha.
`PngEncoder(java.awt.Image image, boolean encodeAlpha, int whichFilter)` Class constructor specifying Image to encode, whether to encode alpha, and filter to use.
`PngEncoder(java.awt.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
`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.
`java.awt.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(java.awt.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 java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### ENCODE_ALPHA

    public static final boolean ENCODE_ALPHA

  Constant specifying that alpha channel should be encoded.

  See Also:
    Constant Field Values

### NO_ALPHA

    public static final boolean NO_ALPHA

  Constant specifying that alpha channel should not be encoded.

  See Also:
    Constant Field Values

### FILTER_NONE

    public static final int FILTER_NONE

  Constants for filter (NONE).

  See Also:
    Constant Field Values

### FILTER_SUB

    public static final int FILTER_SUB

  Constants for filter (SUB).

  See Also:
    Constant Field Values

### FILTER_UP

    public static final int FILTER_UP

  Constants for filter (UP).

  See Also:
    Constant Field Values

### FILTER_LAST

    public static final int FILTER_LAST

  Constants for filter (LAST).

  See Also:
    Constant Field Values

### 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 java.awt.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 java.util.zip.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 Detail

### PngEncoder

    public PngEncoder()

  Class constructor.

### PngEncoder

    public PngEncoder(java.awt.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:
    `Image`

### PngEncoder

    public PngEncoder(java.awt.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:
    `Image`

### PngEncoder

    public PngEncoder(java.awt.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:
    `Image`

### PngEncoder

    public PngEncoder(java.awt.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:
    `Image`

Method Detail

### setImage

    public void setImage(java.awt.Image image)

  Set the image to be encoded.

  Parameters:
    `image` - A Java Image object which uses the DirectColorModel
  See Also:
    `Image`, `DirectColorModel`

### getImage

    public java.awt.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.

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