001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.imaging.formats.png.scanlinefilters;
018
019import java.io.IOException;
020
021import org.apache.commons.imaging.ImagingException;
022
023public class ScanlineFilterSub implements ScanlineFilter {
024    private final int bytesPerPixel;
025
026    public ScanlineFilterSub(final int bytesPerPixel) {
027        this.bytesPerPixel = bytesPerPixel;
028    }
029
030    @Override
031    public void unfilter(final byte[] src, final byte[] dst, final byte[] up) throws ImagingException, IOException {
032        for (int i = 0; i < src.length; i++) {
033            final int prevIndex = i - bytesPerPixel;
034            if (prevIndex >= 0) {
035                dst[i] = (byte) ((src[i] + dst[prevIndex]) % 256);
036                // dst[i] = 0xff & (src[i] + src[prevIndex]);
037            } else {
038                dst[i] = src[i];
039            }
040
041            // if (i<10)
042            // System.out.println("\t" + i + ": " + dst[i] + " (" + src[i] +
043            // ", " + prevIndex + ")");
044
045            // dst[i] = src[i];
046        }
047    }
048}