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Java > Open Source Codes > org > pdfbox > pdmodel > graphics > predictor > Paeth


1 /**
2  * Copyright (c) 2005, www.pdfbox.org
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions are met:
7  *
8  * 1. Redistributions of source code must retain the above copyright notice,
9  * this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright notice,
11  * this list of conditions and the following disclaimer in the documentation
12  * and/or other materials provided with the distribution.
13  * 3. Neither the name of pdfbox; nor the names of its
14  * contributors may be used to endorse or promote products derived from this
15  * software without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20  * DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
24  * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
26  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27  *
28  * http://www.pdfbox.org
29  */
30 package org.pdfbox.pdmodel.graphics.predictor;
31
32 /**
33  * From http://www.w3.org/TR/PNG-Filters.html: The Paeth filter computes a
34  * simple linear function of the three neighboring pixels (left, above, upper
35  * left), then chooses as predictor the neighboring pixel closest to the
36  * computed value. This technique is due to Alan W. Paeth [PAETH].
37  *
38  * To compute the Paeth filter, apply the following formula to each byte of the
39  * scanline:
40  *
41  * <code>Paeth(i,j) = Raw(i,j) - PaethPredictor(Raw(i-1,j), Raw(i,j-1), Raw(i-1,j-1))</code>
42  *
43  * To decode the Paeth filter
44  *
45  * <code>Raw(i,j) = Paeth(i,j) - PaethPredictor(Raw(i-1,j), Raw(i,j-1), Raw(i-1,j-1))</code>
46  *
47  * @author xylifyx@yahoo.co.uk
48  * @version $Revision: 1.3 $
49  */
50 public class Paeth extends PredictorAlgorithm
51 {
52     /**
53      * The paeth predictor function.
54      *
55      * This function is taken almost directly from the PNG definition on
56      * http://www.w3.org/TR/PNG-Filters.html
57      *
58      * @param a
59      * left
60      * @param b
61      * above
62      * @param c
63      * upper left
64      * @return The result of the paeth predictor.
65      */
66     public int paethPredictor(int a, int b, int c)
67     {
68         int p = a + b - c; // initial estimate
69 int pa = Math.abs(p - a); // distances to a, b, c
70 int pb = Math.abs(p - b);
71         int pc = Math.abs(p - c);
72         // return nearest of a,b,c,
73 // breaking ties in order a,b,c.
74 if (pa <= pb && pa <= pc)
75         {
76             return a;
77         }
78         else if (pb <= pc)
79         {
80             return b;
81         }
82         else
83         {
84             return c;
85         }
86     }
87
88     /**
89      * {@inheritDoc}
90      */
91     public void encodeLine(byte[] src, byte[] dest, int srcDy, int srcOffset,
92             int destDy, int destOffset)
93     {
94         int bpl = getWidth() * getBpp();
95         for (int x = 0; x < bpl; x++)
96         {
97             dest[x + destOffset] = (byte) (src[x + srcOffset] - paethPredictor(
98                     leftPixel(src, srcOffset, srcDy, x), abovePixel(src,
99                             srcOffset, srcDy, x), aboveLeftPixel(src,
100                             srcOffset, srcDy, x)));
101         }
102     }
103
104     /**
105      * {@inheritDoc}
106      */
107     public void decodeLine(byte[] src, byte[] dest, int srcDy, int srcOffset,
108             int destDy, int destOffset)
109     {
110         int bpl = getWidth() * getBpp();
111         for (int x = 0; x < bpl; x++)
112         {
113             dest[x + destOffset] = (byte) (src[x + srcOffset] + paethPredictor(
114                     leftPixel(dest, destOffset, destDy, x), abovePixel(dest,
115                             destOffset, destDy, x), aboveLeftPixel(dest,
116                             destOffset, destDy, x)));
117         }
118     }
119 }
120
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