1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.imaging.formats.png.scanlinefilters;
18
19 import java.io.IOException;
20
21 import org.apache.commons.imaging.ImagingException;
22
23 public class ScanlineFilterSub implements ScanlineFilter {
24 private final int bytesPerPixel;
25
26 public ScanlineFilterSub(final int bytesPerPixel) {
27 this.bytesPerPixel = bytesPerPixel;
28 }
29
30 @Override
31 public void unfilter(final byte[] src, final byte[] dst, final byte[] up) throws ImagingException, IOException {
32 for (int i = 0; i < src.length; i++) {
33 final int prevIndex = i - bytesPerPixel;
34 if (prevIndex >= 0) {
35 dst[i] = (byte) ((src[i] + dst[prevIndex]) % 256);
36 // dst[i] = 0xff & (src[i] + src[prevIndex]);
37 } else {
38 dst[i] = src[i];
39 }
40
41 // if (i<10)
42 // System.out.println("\t" + i + ": " + dst[i] + " (" + src[i] +
43 // ", " + prevIndex + ")");
44
45 // dst[i] = src[i];
46 }
47 }
48 }