/*
* 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.
*/
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using com.google.zxing;
using com.google.zxing.common;
namespace com.google.zxing.datamatrix.detector
{
/**
* <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 sealed class Detector
{
private static int MAX_MODULES = 32;
// Trick to avoid creating new int objects below -- a sort of crude copy of
// the int.valueOf(int) optimization added in Java 5, not in J2ME
private static int[] intS =
{0, 1, 2, 3, 4};
private MonochromeBitmapSource image;
public Detector(MonochromeBitmapSource image) {
this.image = image;
}
/**
* <p>Detects a Data Matrix Code in an image.</p>
*
* @return {@link DetectorResult} encapsulating results of detecting a QR Code
* @throws ReaderException if no Data Matrix Code can be found
*/
public DetectorResult detect() {
if (!BlackPointEstimationMethod.TWO_D_SAMPLING.Equals(image.getLastEstimationMethod())) {
image.estimateBlackPoint(BlackPointEstimationMethod.TWO_D_SAMPLING, 0);
}
int height = image.getHeight();
int width = image.getWidth();
int halfHeight = height >> 1;
int halfWidth = width >> 1;
int iSkip = Math.Max(1, height / (MAX_MODULES << 3));
int jSkip = Math.Max(1, width / (MAX_MODULES << 3));
int minI = 0;
int maxI = height;
int minJ = 0;
int maxJ = width;
ResultPoint pointA = findCornerFromCenter(halfHeight, -iSkip, minI, maxI, halfWidth, 0, minJ, maxJ, halfWidth >> 1);
minI = (int) pointA.getY() - 1;
ResultPoint pointB = findCornerFromCenter(halfHeight, 0, minI, maxI, halfWidth, -jSkip, minJ, maxJ, halfHeight >> 1);
minJ = (int) pointB.getX() - 1;
ResultPoint pointC = findCornerFromCenter(halfHeight, 0, minI, maxI, halfWidth, jSkip, minJ, maxJ, halfHeight >> 1);
maxJ = (int) pointC.getX() + 1;
ResultPoint pointD = findCornerFromCenter(halfHeight, iSkip, minI, maxI, halfWidth, 0, minJ, maxJ, halfWidth >> 1);
maxI = (int) pointD.getY() + 1;
// Go try to find point A again with better information -- might have been off at first.
pointA = findCornerFromCenter(halfHeight, -iSkip, minI, maxI, halfWidth, 0, minJ, maxJ, halfWidth >> 2);
// 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
System.Collections.ArrayList transitions = new System.Collections.ArrayList(4);
transitions.Add(transitionsBetween(pointA, pointB));
transitions.Add(transitionsBetween(pointA, pointC));
transitions.Add(transitionsBetween(pointB, pointD));
transitions.Add(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[0];
ResultPointsAndTransitions lSideTwo = (ResultPointsAndTransitions) transitions[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.
System.Collections.Hashtable pointCount = new System.Collections.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;
System.Collections.IEnumerator points = pointCount.GetEnumerator();
while (points.MoveNext()) {
ResultPoint point = (ResultPoint) points.Current;
int value = (int) pointCount[point];
if (value == 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 new ReaderException();
}
// 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
GenericResultPoint.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, but, one will be more reliable since it's traced straight
// up or across, rather than at a slight angle. We use dot products to figure out which is
// better to use:
int dimension;
if (GenericResultPoint.crossProductZ(bottomLeft, bottomRight, topRight) <
GenericResultPoint.crossProductZ(topRight, topLeft, bottomLeft)) {
dimension = transitionsBetween(topLeft, topRight).getTransitions();
} else {
dimension = transitionsBetween(bottomRight, topRight).getTransitions();
}
dimension += 2;
BitMatrix bits = sampleGrid(image, topLeft, bottomLeft, bottomRight, dimension);
return new DetectorResult(bits, new ResultPoint[] {pointA, pointB, pointC, pointD});
}
/**
* Attempts to locate a corner of the barcode by scanning up, down, left or right from a center
* point which should be within the barcode.
*
* @param centerI center's i componennt (vertical)
* @param di change in i per step. If scanning up this is negative; down, positive; left or right, 0
* @param minI minimum value of i to search through (meaningless when di == 0)
* @param maxI maximum value of i
* @param centerJ center's j component (horizontal)
* @param dj same as di but change in j per step instead
* @param minJ see minI
* @param maxJ see minJ
* @param maxWhiteRun maximum run of white pixels that can still be considered to be within
* the barcode
* @return a {@link ResultPoint} encapsulating the corner that was found
* @throws ReaderException if such a point cannot be found
*/
private ResultPoint findCornerFromCenter(int centerI, int di, int minI, int maxI,
int centerJ, int dj, int minJ, int maxJ,
int maxWhiteRun) {
int[] lastRange = null;
for (int i = centerI, j = centerJ;
i < maxI && i >= minI && j < maxJ && j >= minJ;
i += di, j += dj) {
int[] range;
if (dj == 0) {
// horizontal slices, up and down
range = blackWhiteRange(i, maxWhiteRun, minJ, maxJ, true);
} else {
// vertical slices, left and right
range = blackWhiteRange(j, maxWhiteRun, minI, maxI, false);
}
if (range == null) {
if (lastRange == null) {
throw new ReaderException();
}
// lastRange was found
if (dj == 0) {
int lastI = i - di;
if (lastRange[0] < centerJ) {
if (lastRange[1] > centerJ) {
// straddle, choose one or the other based on direction
return new GenericResultPoint(di > 0 ? lastRange[0] : lastRange[1], lastI);
}
return new GenericResultPoint(lastRange[0], lastI);
} else {
return new GenericResultPoint(lastRange[1], lastI);
}
} else {
int lastJ = j - dj;
if (lastRange[0] < centerI) {
if (lastRange[1] > centerI) {
return new GenericResultPoint(lastJ, dj < 0 ? lastRange[0] : lastRange[1]);
}
return new GenericResultPoint(lastJ, lastRange[0]);
} else {
return new GenericResultPoint(lastJ, lastRange[1]);
}
}
}
lastRange = range;
}
throw new ReaderException();
}
/**
* Increments the int associated with a key by one.
*/
private static void increment(System.Collections.Hashtable table, ResultPoint key) {
int value = (int) table[key];
table[key] = value.Equals(null) ? intS[1] : intS[value + 1];
//table.put(key, value == null ? intS[1] : intS[value.intValue() + 1]);
}
/**
* Computes the start and end of a region of pixels, either horizontally or vertically, that could be
* part of a Data Matrix barcode.
*
* @param fixedDimension if scanning horizontally, this is the row (the fixed vertical location) where
* we are scanning. If scanning vertically it's the colummn, the fixed horizontal location
* @param maxWhiteRun largest run of white pixels that can still be considered part of the barcode region
* @param minDim minimum pixel location, horizontally or vertically, to consider
* @param maxDim maximum pixel location, horizontally or vertically, to consider
* @param horizontal if true, we're scanning left-right, instead of up-down
* @return int[] with start and end of found range, or null if no such range is found (e.g. only white was found)
*/
private int[] blackWhiteRange(int fixedDimension, int maxWhiteRun, int minDim, int maxDim, bool horizontal) {
int center = (minDim + maxDim) / 2;
BitArray rowOrColumn = horizontal ? image.getBlackRow(fixedDimension, null, 0, image.getWidth())
: image.getBlackColumn(fixedDimension, null, 0, image.getHeight());
// Scan left/up first
int start = center;
while (start >= minDim) {
if (rowOrColumn.get(start)) {
start--;
} else {
int whiteRunStart = start;
do {
start--;
} while (start >= minDim && !rowOrColumn.get(start));
int whiteRunSize = whiteRunStart - start;
if (start < minDim || whiteRunSize > maxWhiteRun) {
start = whiteRunStart + 1; // back up
break;
}
}
}
start++;
// Then try right/down
int end = center;
while (end < maxDim) {
if (rowOrColumn.get(end)) {
end++;
} else {
int whiteRunStart = end;
do {
end++;
} while (end < maxDim && !rowOrColumn.get(end));
int whiteRunSize = end - whiteRunStart;
if (end >= maxDim || whiteRunSize > maxWhiteRun) {
end = whiteRunStart - 1;
break;
}
}
}
end--;
if (end > start) {
return new int[] { start, end };
} else {
return null;
}
}
private static BitMatrix sampleGrid(MonochromeBitmapSource image,
ResultPoint topLeft,
ResultPoint bottomLeft,
ResultPoint bottomRight,
int dimension) {
// We make up the top right point for now, based on the others.
// TODO: we actually found a fourth corner above and figured out which of two modules
// it was the corner of. We could use that here and adjust for perspective distortion.
float topRightX = (bottomRight.getX() - bottomLeft.getX()) + topLeft.getX();
float topRightY = (bottomRight.getY() - bottomLeft.getY()) + topLeft.getY();
// Note that unlike in the QR Code sampler, we didn't find the center of modules, but the
// very corners. So there is no 0.5f here; 0.0f is right.
GridSampler sampler = GridSampler.Instance;
return sampler.sampleGrid(
image,
dimension,
0.0f,
0.0f,
dimension,
0.0f,
dimension,
dimension,
0.0f,
dimension,
topLeft.getX(),
topLeft.getY(),
topRightX,
topRightY,
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();
bool 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;
bool inBlack = image.isBlack(steep ? fromY : fromX, steep ? fromX : fromY);
for (int x = fromX, y = fromY; x != toX; x += xstep) {
bool isBlack = image.isBlack(steep ? y : x, steep ? x : y);
if (isBlack == !inBlack) {
transitions++;
inBlack = isBlack;
}
error += dy;
if (error > 0) {
y += ystep;
error -= dx;
}
}
return new ResultPointsAndTransitions(from, to, transitions);
}
/**
* Simply encapsulates two points and a number of transitions between them.
*/
private class ResultPointsAndTransitions {
private ResultPoint from;
private ResultPoint to;
private int transitions;
public 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 class ResultPointsAndTransitionsComparator : Comparator {
public int compare(Object o1, Object o2) {
return ((ResultPointsAndTransitions) o1).getTransitions() - ((ResultPointsAndTransitions) o2).getTransitions();
}
}
}
}