Package org.apache.pdfbox.pdmodel.graphics.predictor

Class Paeth

java.lang.Object

org.apache.pdfbox.pdmodel.graphics.predictor.PredictorAlgorithm

org.apache.pdfbox.pdmodel.graphics.predictor.Paeth

public class Paeth
extends PredictorAlgorithm

From http://www.w3.org/TR/PNG-Filters.html: The Paeth filter computes a simple linear function of the three neighboring pixels (left, above, upper left), then chooses as predictor the neighboring pixel closest to the computed value. This technique is due to Alan W. Paeth [PAETH]. To compute the Paeth filter, apply the following formula to each byte of the scanline: Paeth(i,j) = Raw(i,j) - PaethPredictor(Raw(i-1,j), Raw(i,j-1), Raw(i-1,j-1)) To decode the Paeth filter Raw(i,j) = Paeth(i,j) - PaethPredictor(Raw(i-1,j), Raw(i,j-1), Raw(i-1,j-1))

Version:

$Revision: 1.3 $

Author:

xylifyx@yahoo.co.uk

Constructor Summary

Constructors

Constructor	Description
Paeth()

Method Summary

Modifier and Type	Method	Description
void	decodeLine(byte[] src, byte[] dest, int srcDy, int srcOffset, int destDy, int destOffset)	decode line of pixel data in src from src_offset and width*bpp bytes forward, put the decoded bytes into dest.
void	encodeLine(byte[] src, byte[] dest, int srcDy, int srcOffset, int destDy, int destOffset)	encode line of pixel data in src from srcOffset and width*bpp bytes forward, put the decoded bytes into dest.
int	paethPredictor(int a, int b, int c)	The paeth predictor function.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from class org.apache.pdfbox.pdmodel.graphics.predictor.PredictorAlgorithm

aboveLeftPixel, abovePixel, checkBufsiz, decode, encode, getBpp, getFilter, getHeight, getWidth, leftPixel, main, setBpp, setHeight, setWidth

Constructor Detail

Paeth

public Paeth()

Method Detail

paethPredictor

public int paethPredictor(int a,
                          int b,
                          int c)

The paeth predictor function. This function is taken almost directly from the PNG definition on http://www.w3.org/TR/PNG-Filters.html

Parameters:

a - left

b - above

c - upper left

Returns:

The result of the paeth predictor.

encodeLine

public void encodeLine(byte[] src,
                       byte[] dest,
                       int srcDy,
                       int srcOffset,
                       int destDy,
                       int destOffset)

encode line of pixel data in src from srcOffset and width*bpp bytes forward, put the decoded bytes into dest.

Specified by:

encodeLine in class PredictorAlgorithm

Parameters:

src - raw image data

dest - encoded data

srcDy - byte offset between lines

srcOffset - beginning of line data

destDy - byte offset between lines

destOffset - beginning of line data

decodeLine

public void decodeLine(byte[] src,
                       byte[] dest,
                       int srcDy,
                       int srcOffset,
                       int destDy,
                       int destOffset)

decode line of pixel data in src from src_offset and width*bpp bytes forward, put the decoded bytes into dest.

Specified by:

decodeLine in class PredictorAlgorithm

Parameters:

src - encoded image data

dest - raw data

srcDy - byte offset between lines

srcOffset - beginning of line data

destDy - byte offset between lines

destOffset - beginning of line data