org.apache.pdfbox.pdmodel.graphics.predictor: public class: Paeth

org.apache.pdfbox.pdmodel.graphics.predictor
public class: Paeth [javadoc | source]

java.lang.Object
   org.apache.pdfbox.pdmodel.graphics.predictor.PredictorAlgorithm
      org.apache.pdfbox.pdmodel.graphics.predictor.Paeth

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))

author: xylifyx - @yahoo.co.uk

version: $ - Revision: 1.3 $

Method from org.apache.pdfbox.pdmodel.graphics.predictor.Paeth Summary:
decodeLine, encodeLine, paethPredictor

Methods from org.apache.pdfbox.pdmodel.graphics.predictor.PredictorAlgorithm:
aboveLeftPixel, abovePixel, checkBufsiz, decode, decodeLine, encode, encodeLine, getBpp, getFilter, getHeight, getWidth, leftPixel, main, setBpp, setHeight, setWidth

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from org.apache.pdfbox.pdmodel.graphics.predictor.Paeth Detail:
public void decodeLine(byte[] src, byte[] dest, int srcDy, int srcOffset, int destDy, int destOffset) { int bpl = getWidth() * getBpp(); for (int x = 0; x < bpl; x++) { dest[x + destOffset] = (byte) (src[x + srcOffset] + paethPredictor( leftPixel(dest, destOffset, destDy, x), abovePixel(dest, destOffset, destDy, x), aboveLeftPixel(dest, destOffset, destDy, x))); } } {@inheritDoc}
public void encodeLine(byte[] src, byte[] dest, int srcDy, int srcOffset, int destDy, int destOffset) { int bpl = getWidth() * getBpp(); for (int x = 0; x < bpl; x++) { dest[x + destOffset] = (byte) (src[x + srcOffset] - paethPredictor( leftPixel(src, srcOffset, srcDy, x), abovePixel(src, srcOffset, srcDy, x), aboveLeftPixel(src, srcOffset, srcDy, x))); } } {@inheritDoc}
public int paethPredictor(int a, int b, int c) { int p = a + b - c; // initial estimate int pa = Math.abs(p - a); // distances to a, b, c int pb = Math.abs(p - b); int pc = Math.abs(p - c); // return nearest of a,b,c, // breaking ties in order a,b,c. if (pa < = pb && pa < = pc) { return a; } else if (pb < = pc) { return b; } else { return c; } } The paeth predictor function. This function is taken almost directly from the PNG definition on http://www.w3.org/TR/PNG-Filters.html

Method from org.apache.pdfbox.pdmodel.graphics.predictor.Paeth Detail:

 public  void decodeLine(byte[] src,
    byte[] dest,
    int srcDy,
    int srcOffset,
    int destDy,
    int destOffset) {
        int bpl = getWidth() * getBpp();
        for (int x = 0; x <  bpl; x++)
        {
            dest[x + destOffset] = (byte) (src[x + srcOffset] + paethPredictor(
                    leftPixel(dest, destOffset, destDy, x), abovePixel(dest,
                            destOffset, destDy, x), aboveLeftPixel(dest,
                            destOffset, destDy, x)));
        }
}

{@inheritDoc}

 public  void encodeLine(byte[] src,
    byte[] dest,
    int srcDy,
    int srcOffset,
    int destDy,
    int destOffset) {
        int bpl = getWidth() * getBpp();
        for (int x = 0; x <  bpl; x++)
        {
            dest[x + destOffset] = (byte) (src[x + srcOffset] - paethPredictor(
                    leftPixel(src, srcOffset, srcDy, x), abovePixel(src,
                            srcOffset, srcDy, x), aboveLeftPixel(src,
                            srcOffset, srcDy, x)));
        }
}

{@inheritDoc}

 public int paethPredictor(int a,
    int b,
    int c) {
        int p = a + b - c; // initial estimate
        int pa = Math.abs(p - a); // distances to a, b, c
        int pb = Math.abs(p - b);
        int pc = Math.abs(p - c);
        // return nearest of a,b,c,
        // breaking ties in order a,b,c.
        if (pa < = pb && pa < = pc)
        {
            return a;
        }
        else if (pb < = pc)
        {
            return b;
        }
        else
        {
            return c;
        }
}

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