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

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 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

Constructors
Constructor	Description
`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

All Methods Instance Methods Concrete Methods
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.
`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.

Class PngEncoder

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

ENCODE_ALPHA

NO_ALPHA

FILTER_NONE

FILTER_SUB

FILTER_UP

FILTER_LAST

IHDR

IDAT

IEND

PHYS

pngBytes

priorRow

leftBytes

image

width

height

bytePos

maxPos

crc

crcValue

encodeAlpha

filter

bytesPerPixel

compressionLevel

Constructor Detail

PngEncoder

PngEncoder

PngEncoder

PngEncoder

PngEncoder

Method Detail

setImage

getImage

pngEncode

pngEncode

setEncodeAlpha

getEncodeAlpha

setFilter

getFilter

setCompressionLevel

getCompressionLevel

resizeByteArray

writeBytes

writeBytes

writeInt2

writeInt4

writeByte

writeHeader

filterSub

filterUp

writeImageData

writeEnd

setXDpi

getXDpi

setYDpi

getYDpi

setDpi

writeResolution