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 ScanlineFilterAverage implements ScanlineFilter {
024    private final int bytesPerPixel;
025
026    public ScanlineFilterAverage(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            int raw = 0;
034            final int prevIndex = i - bytesPerPixel;
035            if (prevIndex >= 0) {
036                raw = dst[prevIndex];
037            }
038
039            int prior = 0;
040            if (up != null) {
041                prior = up[i];
042            }
043
044            final int average = ((0xff & raw) + (0xff & prior)) / 2;
045
046            dst[i] = (byte) ((src[i] + average) % 256);
047            // dst[i] = src[i];
048            // dst[i] = (byte) 255;
049        }
050    }
051}