    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}