/*
* Copyright (c) 2000, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.sun.imageio.plugins.png;
/**
*/
public class RowFilter {
private static final int abs(int x) {
return (x < 0) ? -x : x;
}
// Returns the sum of absolute differences
protected static int subFilter(byte[] currRow,
byte[] subFilteredRow,
int bytesPerPixel,
int bytesPerRow) {
int badness = 0;
for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
int curr = currRow[i] & 0xff;
int left = currRow[i - bytesPerPixel] & 0xff;
int difference = curr - left;
subFilteredRow[i] = (byte)difference;
badness += abs(difference);
}
return badness;
}
// Returns the sum of absolute differences
protected static int upFilter(byte[] currRow,
byte[] prevRow,
byte[] upFilteredRow,
int bytesPerPixel,
int bytesPerRow) {
int badness = 0;
for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
int curr = currRow[i] & 0xff;
int up = prevRow[i] & 0xff;
int difference = curr - up;
upFilteredRow[i] = (byte)difference;
badness += abs(difference);
}
return badness;
}
protected final int paethPredictor(int a, int b, int c) {
int p = a + b - c;
int pa = abs(p - a);
int pb = abs(p - b);
int pc = abs(p - c);
if ((pa <= pb) && (pa <= pc)) {
return a;
} else if (pb <= pc) {
return b;
} else {
return c;
}
}
public int filterRow(int colorType,
byte[] currRow,
byte[] prevRow,
byte[][] scratchRows,
int bytesPerRow,
int bytesPerPixel) {
// Use type 0 for palette images
if (colorType != PNGImageReader.PNG_COLOR_PALETTE) {
System.arraycopy(currRow, bytesPerPixel,
scratchRows[0], bytesPerPixel,
bytesPerRow);
return 0;
}
int[] filterBadness = new int[5];
for (int i = 0; i < 5; i++) {
filterBadness[i] = Integer.MAX_VALUE;
}
{
int badness = 0;
for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
int curr = currRow[i] & 0xff;
badness += curr;
}
filterBadness[0] = badness;
}
{
byte[] subFilteredRow = scratchRows[1];
int badness = subFilter(currRow,
subFilteredRow,
bytesPerPixel,
bytesPerRow);
filterBadness[1] = badness;
}
{
byte[] upFilteredRow = scratchRows[2];
int badness = upFilter(currRow,
prevRow,
upFilteredRow,
bytesPerPixel,
bytesPerRow);
filterBadness[2] = badness;
}
{
byte[] averageFilteredRow = scratchRows[3];
int badness = 0;
for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
int curr = currRow[i] & 0xff;
int left = currRow[i - bytesPerPixel] & 0xff;
int up = prevRow[i] & 0xff;
int difference = curr - (left + up)/2;;
averageFilteredRow[i] = (byte)difference;
badness += abs(difference);
}
filterBadness[3] = badness;
}
{
byte[] paethFilteredRow = scratchRows[4];
int badness = 0;
for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
int curr = currRow[i] & 0xff;
int left = currRow[i - bytesPerPixel] & 0xff;
int up = prevRow[i] & 0xff;
int upleft = prevRow[i - bytesPerPixel] & 0xff;
int predictor = paethPredictor(left, up, upleft);
int difference = curr - predictor;
paethFilteredRow[i] = (byte)difference;
badness += abs(difference);
}
filterBadness[4] = badness;
}
int minBadness = filterBadness[0];
int filterType = 0;
for (int i = 1; i < 5; i++) {
if (filterBadness[i] < minBadness) {
minBadness = filterBadness[i];
filterType = i;
}
}
if (filterType == 0) {
System.arraycopy(currRow, bytesPerPixel,
scratchRows[0], bytesPerPixel,
bytesPerRow);
}
return filterType;
}
}