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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA A copy of the GNU LGPL may be found at http://www.gnu.org/copyleft/lesser.html,

Version:

1.4, 31 March 2000 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);

Author:

J. David Eisenberg

Field Summary

Fields

Modifier and Type	Field and Description
static boolean	ENCODE_ALPHA Constant specifying that alpha channel should be encoded.
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)
static boolean	NO_ALPHA Constant specifying that alpha channel should not be encoded.

Constructor Summary

Constructors

Constructor and 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

Methods

Modifier and Type	Method and 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
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	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
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.

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

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

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.