Detector.java
/*
* 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.DetectorResult;
import com.google.zxing.common.GridSampler;
import com.google.zxing.common.detector.WhiteRectangleDetector;
/**
* <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 {
private final BitMatrix image;
private final WhiteRectangleDetector rectangleDetector;
public Detector(BitMatrix image) throws NotFoundException {
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[] points = detectSolid1(cornerPoints);
points = detectSolid2(points);
points[3] = correctTopRight(points);
if (points[3] == null) {
throw NotFoundException.getNotFoundInstance();
}
points = shiftToModuleCenter(points);
ResultPoint topLeft = points[0];
ResultPoint bottomLeft = points[1];
ResultPoint bottomRight = points[2];
ResultPoint topRight = points[3];
int dimensionTop = transitionsBetween(topLeft, topRight) + 1;
int dimensionRight = transitionsBetween(bottomRight, topRight) + 1;
if ((dimensionTop & 0x01) == 1) {
dimensionTop += 1;
}
if ((dimensionRight & 0x01) == 1) {
dimensionRight += 1;
}
if (4 * dimensionTop < 6 * dimensionRight && 4 * dimensionRight < 6 * dimensionTop) {
// The matrix is square
dimensionTop = dimensionRight = Math.max(dimensionTop, dimensionRight);
}
BitMatrix bits = sampleGrid(image,
topLeft,
bottomLeft,
bottomRight,
topRight,
dimensionTop,
dimensionRight);
return new DetectorResult(bits, new ResultPoint[]{topLeft, bottomLeft, bottomRight, topRight});
}
private static ResultPoint shiftPoint(ResultPoint point, ResultPoint to, int div) {
float x = (to.getX() - point.getX()) / (div + 1);
float y = (to.getY() - point.getY()) / (div + 1);
return new ResultPoint(point.getX() + x, point.getY() + y);
}
private static ResultPoint moveAway(ResultPoint point, float fromX, float fromY) {
float x = point.getX();
float y = point.getY();
if (x < fromX) {
x -= 1;
} else {
x += 1;
}
if (y < fromY) {
y -= 1;
} else {
y += 1;
}
return new ResultPoint(x, y);
}
/**
* Detect a solid side which has minimum transition.
*/
private ResultPoint[] detectSolid1(ResultPoint[] cornerPoints) {
// 0 2
// 1 3
ResultPoint pointA = cornerPoints[0];
ResultPoint pointB = cornerPoints[1];
ResultPoint pointC = cornerPoints[3];
ResultPoint pointD = cornerPoints[2];
int trAB = transitionsBetween(pointA, pointB);
int trBC = transitionsBetween(pointB, pointC);
int trCD = transitionsBetween(pointC, pointD);
int trDA = transitionsBetween(pointD, pointA);
// 0..3
// : :
// 1--2
int min = trAB;
ResultPoint[] points = {pointD, pointA, pointB, pointC};
if (min > trBC) {
min = trBC;
points[0] = pointA;
points[1] = pointB;
points[2] = pointC;
points[3] = pointD;
}
if (min > trCD) {
min = trCD;
points[0] = pointB;
points[1] = pointC;
points[2] = pointD;
points[3] = pointA;
}
if (min > trDA) {
points[0] = pointC;
points[1] = pointD;
points[2] = pointA;
points[3] = pointB;
}
return points;
}
/**
* Detect a second solid side next to first solid side.
*/
private ResultPoint[] detectSolid2(ResultPoint[] points) {
// A..D
// : :
// B--C
ResultPoint pointA = points[0];
ResultPoint pointB = points[1];
ResultPoint pointC = points[2];
ResultPoint pointD = points[3];
// Transition detection on the edge is not stable.
// To safely detect, shift the points to the module center.
int tr = transitionsBetween(pointA, pointD);
ResultPoint pointBs = shiftPoint(pointB, pointC, (tr + 1) * 4);
ResultPoint pointCs = shiftPoint(pointC, pointB, (tr + 1) * 4);
int trBA = transitionsBetween(pointBs, pointA);
int trCD = transitionsBetween(pointCs, pointD);
// 0..3
// | :
// 1--2
if (trBA < trCD) {
// solid sides: A-B-C
points[0] = pointA;
points[1] = pointB;
points[2] = pointC;
points[3] = pointD;
} else {
// solid sides: B-C-D
points[0] = pointB;
points[1] = pointC;
points[2] = pointD;
points[3] = pointA;
}
return points;
}
/**
* Calculates the corner position of the white top right module.
*/
private ResultPoint correctTopRight(ResultPoint[] points) {
// A..D
// | :
// B--C
ResultPoint pointA = points[0];
ResultPoint pointB = points[1];
ResultPoint pointC = points[2];
ResultPoint pointD = points[3];
// shift points for safe transition detection.
int trTop = transitionsBetween(pointA, pointD);
int trRight = transitionsBetween(pointB, pointD);
ResultPoint pointAs = shiftPoint(pointA, pointB, (trRight + 1) * 4);
ResultPoint pointCs = shiftPoint(pointC, pointB, (trTop + 1) * 4);
trTop = transitionsBetween(pointAs, pointD);
trRight = transitionsBetween(pointCs, pointD);
ResultPoint candidate1 = new ResultPoint(
pointD.getX() + (pointC.getX() - pointB.getX()) / (trTop + 1),
pointD.getY() + (pointC.getY() - pointB.getY()) / (trTop + 1));
ResultPoint candidate2 = new ResultPoint(
pointD.getX() + (pointA.getX() - pointB.getX()) / (trRight + 1),
pointD.getY() + (pointA.getY() - pointB.getY()) / (trRight + 1));
if (!isValid(candidate1)) {
if (isValid(candidate2)) {
return candidate2;
}
return null;
}
if (!isValid(candidate2)) {
return candidate1;
}
int sumc1 = transitionsBetween(pointAs, candidate1) + transitionsBetween(pointCs, candidate1);
int sumc2 = transitionsBetween(pointAs, candidate2) + transitionsBetween(pointCs, candidate2);
if (sumc1 > sumc2) {
return candidate1;
} else {
return candidate2;
}
}
/**
* Shift the edge points to the module center.
*/
private ResultPoint[] shiftToModuleCenter(ResultPoint[] points) {
// A..D
// | :
// B--C
ResultPoint pointA = points[0];
ResultPoint pointB = points[1];
ResultPoint pointC = points[2];
ResultPoint pointD = points[3];
// calculate pseudo dimensions
int dimH = transitionsBetween(pointA, pointD) + 1;
int dimV = transitionsBetween(pointC, pointD) + 1;
// shift points for safe dimension detection
ResultPoint pointAs = shiftPoint(pointA, pointB, dimV * 4);
ResultPoint pointCs = shiftPoint(pointC, pointB, dimH * 4);
// calculate more precise dimensions
dimH = transitionsBetween(pointAs, pointD) + 1;
dimV = transitionsBetween(pointCs, pointD) + 1;
if ((dimH & 0x01) == 1) {
dimH += 1;
}
if ((dimV & 0x01) == 1) {
dimV += 1;
}
// WhiteRectangleDetector returns points inside of the rectangle.
// I want points on the edges.
float centerX = (pointA.getX() + pointB.getX() + pointC.getX() + pointD.getX()) / 4;
float centerY = (pointA.getY() + pointB.getY() + pointC.getY() + pointD.getY()) / 4;
pointA = moveAway(pointA, centerX, centerY);
pointB = moveAway(pointB, centerX, centerY);
pointC = moveAway(pointC, centerX, centerY);
pointD = moveAway(pointD, centerX, centerY);
ResultPoint pointBs;
ResultPoint pointDs;
// shift points to the center of each modules
pointAs = shiftPoint(pointA, pointB, dimV * 4);
pointAs = shiftPoint(pointAs, pointD, dimH * 4);
pointBs = shiftPoint(pointB, pointA, dimV * 4);
pointBs = shiftPoint(pointBs, pointC, dimH * 4);
pointCs = shiftPoint(pointC, pointD, dimV * 4);
pointCs = shiftPoint(pointCs, pointB, dimH * 4);
pointDs = shiftPoint(pointD, pointC, dimV * 4);
pointDs = shiftPoint(pointDs, pointA, dimH * 4);
return new ResultPoint[]{pointAs, pointBs, pointCs, pointDs};
}
private boolean isValid(ResultPoint p) {
return p.getX() >= 0 && p.getX() <= image.getWidth() - 1 && p.getY() > 0 && p.getY() <= image.getHeight() - 1;
}
private static BitMatrix sampleGrid(BitMatrix image,
ResultPoint topLeft,
ResultPoint bottomLeft,
ResultPoint bottomRight,
ResultPoint topRight,
int dimensionX,
int dimensionY) throws NotFoundException {
GridSampler sampler = GridSampler.getInstance();
return sampler.sampleGrid(image,
dimensionX,
dimensionY,
0.5f,
0.5f,
dimensionX - 0.5f,
0.5f,
dimensionX - 0.5f,
dimensionY - 0.5f,
0.5f,
dimensionY - 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 int 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 = Math.min(image.getHeight() - 1, (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 / 2;
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 transitions;
}
}