/*
* Copyright 2008 ZXing authors
*
* Licensed 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 com.google.zxing.datamatrix.detector;
import com.google.zxing.NotFoundException;
import com.google.zxing.ResultPoint;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.common.Collections;
import com.google.zxing.common.Comparator;
import com.google.zxing.common.DetectorResult;
import com.google.zxing.common.GridSampler;
import com.google.zxing.common.detector.WhiteRectangleDetector;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Vector;
/**
* <p>Encapsulates logic that can detect a Data Matrix Code in an image, even if the Data Matrix Code
* is rotated or skewed, or partially obscured.</p>
*
* @author Sean Owen
*/
public final class Detector {
// Trick to avoid creating new Integer objects below -- a sort of crude copy of
// the Integer.valueOf(int) optimization added in Java 5, not in J2ME
private static final Integer[] INTEGERS =
{ new Integer(0), new Integer(1), new Integer(2), new Integer(3), new Integer(4) };
// No, can't use valueOf()
private final BitMatrix image;
private final WhiteRectangleDetector rectangleDetector;
public Detector(BitMatrix image) {
this.image = image;
rectangleDetector = new WhiteRectangleDetector(image);
}
/**
* <p>Detects a Data Matrix Code in an image.</p>
*
* @return {@link DetectorResult} encapsulating results of detecting a Data Matrix Code
* @throws NotFoundException if no Data Matrix Code can be found
*/
public DetectorResult detect() throws NotFoundException {
ResultPoint[] cornerPoints = rectangleDetector.detect();
ResultPoint pointA = cornerPoints[0];
ResultPoint pointB = cornerPoints[1];
ResultPoint pointC = cornerPoints[2];
ResultPoint pointD = cornerPoints[3];
// Point A and D are across the diagonal from one another,
// as are B and C. Figure out which are the solid black lines
// by counting transitions
Vector transitions = new Vector(4);
transitions.addElement(transitionsBetween(pointA, pointB));
transitions.addElement(transitionsBetween(pointA, pointC));
transitions.addElement(transitionsBetween(pointB, pointD));
transitions.addElement(transitionsBetween(pointC, pointD));
Collections.insertionSort(transitions, new ResultPointsAndTransitionsComparator());
// Sort by number of transitions. First two will be the two solid sides; last two
// will be the two alternating black/white sides
ResultPointsAndTransitions lSideOne = (ResultPointsAndTransitions) transitions.elementAt(0);
ResultPointsAndTransitions lSideTwo = (ResultPointsAndTransitions) transitions.elementAt(1);
// Figure out which point is their intersection by tallying up the number of times we see the
// endpoints in the four endpoints. One will show up twice.
Hashtable pointCount = new Hashtable();
increment(pointCount, lSideOne.getFrom());
increment(pointCount, lSideOne.getTo());
increment(pointCount, lSideTwo.getFrom());
increment(pointCount, lSideTwo.getTo());
ResultPoint maybeTopLeft = null;
ResultPoint bottomLeft = null;
ResultPoint maybeBottomRight = null;
Enumeration points = pointCount.keys();
while (points.hasMoreElements()) {
ResultPoint point = (ResultPoint) points.nextElement();
Integer value = (Integer) pointCount.get(point);
if (value.intValue() == 2) {
bottomLeft = point; // this is definitely the bottom left, then -- end of two L sides
} else {
// Otherwise it's either top left or bottom right -- just assign the two arbitrarily now
if (maybeTopLeft == null) {
maybeTopLeft = point;
} else {
maybeBottomRight = point;
}
}
}
if (maybeTopLeft == null || bottomLeft == null || maybeBottomRight == null) {
throw NotFoundException.getNotFoundInstance();
}
// Bottom left is correct but top left and bottom right might be switched
ResultPoint[] corners = { maybeTopLeft, bottomLeft, maybeBottomRight };
// Use the dot product trick to sort them out
ResultPoint.orderBestPatterns(corners);
// Now we know which is which:
ResultPoint bottomRight = corners[0];
bottomLeft = corners[1];
ResultPoint topLeft = corners[2];
// Which point didn't we find in relation to the "L" sides? that's the top right corner
ResultPoint topRight;
if (!pointCount.containsKey(pointA)) {
topRight = pointA;
} else if (!pointCount.containsKey(pointB)) {
topRight = pointB;
} else if (!pointCount.containsKey(pointC)) {
topRight = pointC;
} else {
topRight = pointD;
}
// Next determine the dimension by tracing along the top or right side and counting black/white
// transitions. Since we start inside a black module, we should see a number of transitions
// equal to 1 less than the code dimension. Well, actually 2 less, because we are going to
// end on a black module:
// The top right point is actually the corner of a module, which is one of the two black modules
// adjacent to the white module at the top right. Tracing to that corner from either the top left
// or bottom right should work here.
int dimension = Math.min(transitionsBetween(topLeft, topRight).getTransitions(),
transitionsBetween(bottomRight, topRight).getTransitions());
if ((dimension & 0x01) == 1) {
// it can't be odd, so, round... up?
dimension++;
}
dimension += 2;
//correct top right point to match the white module
ResultPoint correctedTopRight = correctTopRight(bottomLeft, bottomRight, topLeft, topRight, dimension);
if (correctedTopRight == null){
correctedTopRight = topRight;
}
//We redetermine the dimension using the corrected top right point
int dimension2 = Math.max(transitionsBetween(topLeft, correctedTopRight).getTransitions(),
transitionsBetween(bottomRight, correctedTopRight).getTransitions());
dimension2++;
if ((dimension2 & 0x01) == 1) {
dimension2++;
}
BitMatrix bits = sampleGrid(image, topLeft, bottomLeft, bottomRight, correctedTopRight, dimension2);
return new DetectorResult(bits, new ResultPoint[]{topLeft, bottomLeft, bottomRight, correctedTopRight});
}
/**
* Calculates the position of the white top right module using the output of the rectangle detector
*/
private ResultPoint correctTopRight(ResultPoint bottomLeft,
ResultPoint bottomRight,
ResultPoint topLeft,
ResultPoint topRight,
int dimension) {
float corr = distance(bottomLeft, bottomRight) / (float)dimension;
int norm = distance(topLeft, topRight);
float cos = (topRight.getX() - topLeft.getX()) / norm;
float sin = (topRight.getY() - topLeft.getY()) / norm;
ResultPoint c1 = new ResultPoint(topRight.getX()+corr*cos, topRight.getY()+corr*sin);
corr = distance(bottomLeft, bottomRight) / (float)dimension;
norm = distance(bottomRight, topRight);
cos = (topRight.getX() - bottomRight.getX()) / norm;
sin = (topRight.getY() - bottomRight.getY()) / norm;
ResultPoint c2 = new ResultPoint(topRight.getX()+corr*cos, topRight.getY()+corr*sin);
if (!isValid(c1)){
if (isValid(c2)){
return c2;
}
return null;
} else if (!isValid(c2)){
return c1;
}
int l1 = Math.abs(transitionsBetween(topLeft, c1).getTransitions() - transitionsBetween(bottomRight, c1).getTransitions());
int l2 = Math.abs(transitionsBetween(topLeft, c2).getTransitions() - transitionsBetween(bottomRight, c2).getTransitions());
if (l1 <= l2){
return c1;
}
return c2;
}
private boolean isValid(ResultPoint p) {
return (p.getX() >= 0 && p.getX() < image.width && p.getY() > 0 && p.getY() < image.height);
}
/**
* Ends up being a bit faster than Math.round(). This merely rounds its
* argument to the nearest int, where x.5 rounds up.
*/
private static int round(float d) {
return (int) (d + 0.5f);
}
// L2 distance
private static int distance(ResultPoint a, ResultPoint b) {
return round((float) Math.sqrt((a.getX() - b.getX())
* (a.getX() - b.getX()) + (a.getY() - b.getY())
* (a.getY() - b.getY())));
}
/**
* Increments the Integer associated with a key by one.
*/
private static void increment(Hashtable table, ResultPoint key) {
Integer value = (Integer) table.get(key);
table.put(key, value == null ? INTEGERS[1] : INTEGERS[value.intValue() + 1]);
}
private static BitMatrix sampleGrid(BitMatrix image,
ResultPoint topLeft,
ResultPoint bottomLeft,
ResultPoint bottomRight,
ResultPoint topRight,
int dimension) throws NotFoundException {
GridSampler sampler = GridSampler.getInstance();
return sampler.sampleGrid(image,
dimension,
0.5f,
0.5f,
dimension - 0.5f,
0.5f,
dimension - 0.5f,
dimension - 0.5f,
0.5f,
dimension - 0.5f,
topLeft.getX(),
topLeft.getY(),
topRight.getX(),
topRight.getY(),
bottomRight.getX(),
bottomRight.getY(),
bottomLeft.getX(),
bottomLeft.getY());
}
/**
* Counts the number of black/white transitions between two points, using something like Bresenham's algorithm.
*/
private ResultPointsAndTransitions transitionsBetween(ResultPoint from, ResultPoint to) {
// See QR Code Detector, sizeOfBlackWhiteBlackRun()
int fromX = (int) from.getX();
int fromY = (int) from.getY();
int toX = (int) to.getX();
int toY = (int) to.getY();
boolean steep = Math.abs(toY - fromY) > Math.abs(toX - fromX);
if (steep) {
int temp = fromX;
fromX = fromY;
fromY = temp;
temp = toX;
toX = toY;
toY = temp;
}
int dx = Math.abs(toX - fromX);
int dy = Math.abs(toY - fromY);
int error = -dx >> 1;
int ystep = fromY < toY ? 1 : -1;
int xstep = fromX < toX ? 1 : -1;
int transitions = 0;
boolean inBlack = image.get(steep ? fromY : fromX, steep ? fromX : fromY);
for (int x = fromX, y = fromY; x != toX; x += xstep) {
boolean isBlack = image.get(steep ? y : x, steep ? x : y);
if (isBlack != inBlack) {
transitions++;
inBlack = isBlack;
}
error += dy;
if (error > 0) {
if (y == toY) {
break;
}
y += ystep;
error -= dx;
}
}
return new ResultPointsAndTransitions(from, to, transitions);
}
/**
* Simply encapsulates two points and a number of transitions between them.
*/
private static class ResultPointsAndTransitions {
private final ResultPoint from;
private final ResultPoint to;
private final int transitions;
private ResultPointsAndTransitions(ResultPoint from, ResultPoint to, int transitions) {
this.from = from;
this.to = to;
this.transitions = transitions;
}
public ResultPoint getFrom() {
return from;
}
public ResultPoint getTo() {
return to;
}
public int getTransitions() {
return transitions;
}
public String toString() {
return from + "/" + to + '/' + transitions;
}
}
/**
* Orders ResultPointsAndTransitions by number of transitions, ascending.
*/
private static class ResultPointsAndTransitionsComparator implements Comparator {
public int compare(Object o1, Object o2) {
return ((ResultPointsAndTransitions) o1).getTransitions() - ((ResultPointsAndTransitions) o2).getTransitions();
}
}
}