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
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

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 java.lang.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:
  
  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
- 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:
  
  Image
- 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:
  
  Image
- 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:
  
  Image
- 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:
  
  Image
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:
  
  Image
  
  DirectColorModel
- getImage
  
  public Image getImage()
  
  Returns the image to be encoded.
- 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 Details

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 Details

PngEncoder

PngEncoder

PngEncoder

PngEncoder

PngEncoder

Method Details

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