Class PngEncoder
- java.lang.Object
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- com.keypoint.PngEncoder
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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
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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 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 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.
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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.
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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.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.
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Field Detail
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ENCODE_ALPHA
public static final boolean ENCODE_ALPHA
Constant specifying that alpha channel should be encoded.- See Also:
- Constant Field Values
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NO_ALPHA
public static final boolean NO_ALPHA
Constant specifying that alpha channel should not be encoded.- See Also:
- Constant Field Values
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FILTER_NONE
public static final int FILTER_NONE
Constants for filter (NONE).- See Also:
- Constant Field Values
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FILTER_SUB
public static final int FILTER_SUB
Constants for filter (SUB).- See Also:
- Constant Field Values
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FILTER_UP
public static final int FILTER_UP
Constants for filter (UP).- See Also:
- Constant Field Values
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FILTER_LAST
public static final int FILTER_LAST
Constants for filter (LAST).- See Also:
- Constant Field Values
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IHDR
protected static final byte[] IHDR
IHDR tag.
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IDAT
protected static final byte[] IDAT
IDAT tag.
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IEND
protected static final byte[] IEND
IEND tag.
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PHYS
protected static final byte[] PHYS
PHYS tag.
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pngBytes
protected byte[] pngBytes
The png bytes.
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priorRow
protected byte[] priorRow
The prior row.
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leftBytes
protected byte[] leftBytes
The left bytes.
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image
protected Image image
The image.
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width
protected int width
The width.
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height
protected int height
The height.
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bytePos
protected int bytePos
The byte position.
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maxPos
protected int maxPos
The maximum position.
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crc
protected CRC32 crc
CRC.
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crcValue
protected long crcValue
The CRC value.
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encodeAlpha
protected boolean encodeAlpha
Encode alpha?
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filter
protected int filter
The filter type.
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bytesPerPixel
protected int bytesPerPixel
The bytes-per-pixel.
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compressionLevel
protected int compressionLevel
The compression level (1 = best speed, 9 = best compression, 0 = no compression).
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Constructor Detail
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PngEncoder
public PngEncoder()
Class constructor.
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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:
Image
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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 DirectColorModelencodeAlpha
- Encode the alpha channel? false=no; true=yes- See Also:
Image
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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 DirectColorModelencodeAlpha
- Encode the alpha channel? false=no; true=yeswhichFilter
- 0=none, 1=sub, 2=up- See Also:
Image
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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 objectencodeAlpha
- Encode the alpha channel? false=no; true=yeswhichFilter
- 0=none, 1=sub, 2=upcompLevel
- 0..9 (1 = best speed, 9 = best compression, 0 = no compression)- See Also:
Image
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Method Detail
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setImage
public void setImage(Image image)
Set the image to be encoded.- Parameters:
image
- A Java Image object which uses the DirectColorModel- See Also:
Image
,DirectColorModel
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getImage
public Image getImage()
Returns the image to be encoded.- Returns:
- The image.
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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
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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
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setEncodeAlpha
public void setEncodeAlpha(boolean encodeAlpha)
Set the alpha encoding on or off.- Parameters:
encodeAlpha
- false=no, true=yes
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getEncodeAlpha
public boolean getEncodeAlpha()
Retrieve alpha encoding status.- Returns:
- boolean false=no, true=yes
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setFilter
public void setFilter(int whichFilter)
Set the filter to use.- Parameters:
whichFilter
- from constant list
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getFilter
public int getFilter()
Retrieve filtering scheme.- Returns:
- int (see constant list)
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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)
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getCompressionLevel
public int getCompressionLevel()
Retrieve compression level.- Returns:
- int (1 = best speed, 9 = best compression, 0 = no compression)
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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.
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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.
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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.
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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.
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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.
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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.
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writeHeader
protected void writeHeader()
Write a PNG "IHDR" chunk into the pngBytes array.
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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 builtstartPos
- Starting position within pixels of bytes to be filtered.width
- Width of a scanline in pixels.
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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 builtstartPos
- Starting position within pixels of bytes to be filtered.width
- Width of a scanline in pixels.
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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
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writeEnd
protected void writeEnd()
Write a PNG "IEND" chunk into the pngBytes array.
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setXDpi
public void setXDpi(int xDpi)
Set the DPI for the X axis.- Parameters:
xDpi
- The number of dots per inch
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getXDpi
public int getXDpi()
Get the DPI for the X axis.- Returns:
- The number of dots per inch
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setYDpi
public void setYDpi(int yDpi)
Set the DPI for the Y axis.- Parameters:
yDpi
- The number of dots per inch
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getYDpi
public int getYDpi()
Get the DPI for the Y axis.- Returns:
- The number of dots per inch
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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.
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writeResolution
protected void writeResolution()
Write a PNG "pHYs" chunk into the pngBytes array.
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