org.apache.commons.imaging.formats.png.scanlinefilters.ScanlineFilterPaeth Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.imaging.formats.png.scanlinefilters;
import java.io.IOException;
import org.apache.commons.imaging.ImageReadException;
public class ScanlineFilterPaeth implements ScanlineFilter {
private final int bytesPerPixel;
public ScanlineFilterPaeth(final int bytesPerPixel) {
this.bytesPerPixel = bytesPerPixel;
}
private int paethPredictor(final int a, final int b, final int c) {
// ; a = left, b = above, c = upper left
final int p = a + b - c; // ; initial estimate
final int pa = Math.abs(p - a); // ; distances to a, b, c
final int pb = Math.abs(p - b);
final int pc = Math.abs(p - c);
// ; return nearest of a,b,c,
// ; breaking ties in order a,b,c.
if ((pa <= pb) && (pa <= pc)) {
return a;
} else if (pb <= pc) {
return b;
} else {
return c;
}
}
@Override
public void unfilter(final byte[] src, final byte[] dst, final byte[] up)
throws ImageReadException, IOException {
for (int i = 0; i < src.length; i++) {
int left = 0;
final int prevIndex = i - bytesPerPixel;
if (prevIndex >= 0) {
left = dst[prevIndex];
}
int above = 0;
if (up != null) {
above = up[i];
}
// above = 255;
int upperleft = 0;
if ((prevIndex >= 0) && (up != null)) {
upperleft = up[prevIndex];
}
// upperleft = 255;
final int paethPredictor = paethPredictor(0xff & left, 0xff & above, 0xff & upperleft);
dst[i] = (byte) ((src[i] + paethPredictor) % 256);
// dst[i] = (byte) ((src[i] + paethPredictor) );
// dst[i] = src[i];
// dst[i] = (byte) 0;
}
}
}