zxing/csharp/qrcode/detector/FinderPatternFinder.cs
2013-01-18 20:14:03 +00:00

675 lines
21 KiB
C#
Executable file

using System;
using System.Collections.Generic;
/*
* Copyright 2007 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.
*/
namespace com.google.zxing.qrcode.detector
{
using DecodeHintType = com.google.zxing.DecodeHintType;
using NotFoundException = com.google.zxing.NotFoundException;
using ResultPoint = com.google.zxing.ResultPoint;
using ResultPointCallback = com.google.zxing.ResultPointCallback;
using BitMatrix = com.google.zxing.common.BitMatrix;
/// <summary>
/// <p>This class attempts to find finder patterns in a QR Code. Finder patterns are the square
/// markers at three corners of a QR Code.</p>
///
/// <p>This class is thread-safe but not reentrant. Each thread must allocate its own object.
///
/// @author Sean Owen
/// </summary>
public class FinderPatternFinder
{
private const int CENTER_QUORUM = 2;
protected internal const int MIN_SKIP = 3; // 1 pixel/module times 3 modules/center
protected internal const int MAX_MODULES = 57; // support up to version 10 for mobile clients
private const int INTEGER_MATH_SHIFT = 8;
private readonly BitMatrix image;
private readonly List<FinderPattern> possibleCenters;
private bool hasSkipped;
private readonly int[] crossCheckStateCount;
private readonly ResultPointCallback resultPointCallback;
/// <summary>
/// <p>Creates a finder that will search the image for three finder patterns.</p>
/// </summary>
/// <param name="image"> image to search </param>
public FinderPatternFinder(BitMatrix image) : this(image, null)
{
}
public FinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback)
{
this.image = image;
this.possibleCenters = new List<FinderPattern>();
this.crossCheckStateCount = new int[5];
this.resultPointCallback = resultPointCallback;
}
protected internal BitMatrix Image
{
get
{
return image;
}
}
protected internal List<FinderPattern> PossibleCenters
{
get
{
return possibleCenters;
}
}
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in .NET:
//ORIGINAL LINE: final FinderPatternInfo find(java.util.Map<com.google.zxing.DecodeHintType,?> hints) throws com.google.zxing.NotFoundException
internal FinderPatternInfo find(IDictionary<DecodeHintType, object> hints)
{
bool tryHarder = hints != null && hints.ContainsKey(DecodeHintType.TRY_HARDER);
int maxI = image.Height;
int maxJ = image.Width;
// We are looking for black/white/black/white/black modules in
// 1:1:3:1:1 ratio; this tracks the number of such modules seen so far
// Let's assume that the maximum version QR Code we support takes up 1/4 the height of the
// image, and then account for the center being 3 modules in size. This gives the smallest
// number of pixels the center could be, so skip this often. When trying harder, look for all
// QR versions regardless of how dense they are.
int iSkip = (3 * maxI) / (4 * MAX_MODULES);
if (iSkip < MIN_SKIP || tryHarder)
{
iSkip = MIN_SKIP;
}
bool done = false;
int[] stateCount = new int[5];
for (int i = iSkip - 1; i < maxI && !done; i += iSkip)
{
// Get a row of black/white values
stateCount[0] = 0;
stateCount[1] = 0;
stateCount[2] = 0;
stateCount[3] = 0;
stateCount[4] = 0;
int currentState = 0;
for (int j = 0; j < maxJ; j++)
{
if (image.get(j, i))
{
// Black pixel
if ((currentState & 1) == 1) // Counting white pixels
{
currentState++;
}
stateCount[currentState]++;
} // White pixel
else
{
if ((currentState & 1) == 0) // Counting black pixels
{
if (currentState == 4) // A winner?
{
if (foundPatternCross(stateCount)) // Yes
{
bool confirmed = handlePossibleCenter(stateCount, i, j);
if (confirmed)
{
// Start examining every other line. Checking each line turned out to be too
// expensive and didn't improve performance.
iSkip = 2;
if (hasSkipped)
{
done = haveMultiplyConfirmedCenters();
}
else
{
int rowSkip = findRowSkip();
if (rowSkip > stateCount[2])
{
// Skip rows between row of lower confirmed center
// and top of presumed third confirmed center
// but back up a bit to get a full chance of detecting
// it, entire width of center of finder pattern
// Skip by rowSkip, but back off by stateCount[2] (size of last center
// of pattern we saw) to be conservative, and also back off by iSkip which
// is about to be re-added
i += rowSkip - stateCount[2] - iSkip;
j = maxJ - 1;
}
}
}
else
{
stateCount[0] = stateCount[2];
stateCount[1] = stateCount[3];
stateCount[2] = stateCount[4];
stateCount[3] = 1;
stateCount[4] = 0;
currentState = 3;
continue;
}
// Clear state to start looking again
currentState = 0;
stateCount[0] = 0;
stateCount[1] = 0;
stateCount[2] = 0;
stateCount[3] = 0;
stateCount[4] = 0;
} // No, shift counts back by two
else
{
stateCount[0] = stateCount[2];
stateCount[1] = stateCount[3];
stateCount[2] = stateCount[4];
stateCount[3] = 1;
stateCount[4] = 0;
currentState = 3;
}
}
else
{
stateCount[++currentState]++;
}
} // Counting white pixels
else
{
stateCount[currentState]++;
}
}
}
if (foundPatternCross(stateCount))
{
bool confirmed = handlePossibleCenter(stateCount, i, maxJ);
if (confirmed)
{
iSkip = stateCount[0];
if (hasSkipped)
{
// Found a third one
done = haveMultiplyConfirmedCenters();
}
}
}
}
FinderPattern[] patternInfo = selectBestPatterns();
ResultPoint.orderBestPatterns(patternInfo);
return new FinderPatternInfo(patternInfo);
}
/// <summary>
/// Given a count of black/white/black/white/black pixels just seen and an end position,
/// figures the location of the center of this run.
/// </summary>
private static float centerFromEnd(int[] stateCount, int end)
{
return (float)(end - stateCount[4] - stateCount[3]) - stateCount[2] / 2.0f;
}
/// <param name="stateCount"> count of black/white/black/white/black pixels just read </param>
/// <returns> true iff the proportions of the counts is close enough to the 1/1/3/1/1 ratios
/// used by finder patterns to be considered a match </returns>
protected internal static bool foundPatternCross(int[] stateCount)
{
int totalModuleSize = 0;
for (int i = 0; i < 5; i++)
{
int count = stateCount[i];
if (count == 0)
{
return false;
}
totalModuleSize += count;
}
if (totalModuleSize < 7)
{
return false;
}
int moduleSize = (totalModuleSize << INTEGER_MATH_SHIFT) / 7;
int maxVariance = moduleSize / 2;
// Allow less than 50% variance from 1-1-3-1-1 proportions
return Math.Abs(moduleSize - (stateCount[0] << INTEGER_MATH_SHIFT)) < maxVariance && Math.Abs(moduleSize - (stateCount[1] << INTEGER_MATH_SHIFT)) < maxVariance && Math.Abs(3 * moduleSize - (stateCount[2] << INTEGER_MATH_SHIFT)) < 3 * maxVariance && Math.Abs(moduleSize - (stateCount[3] << INTEGER_MATH_SHIFT)) < maxVariance && Math.Abs(moduleSize - (stateCount[4] << INTEGER_MATH_SHIFT)) < maxVariance;
}
private int[] CrossCheckStateCount
{
get
{
crossCheckStateCount[0] = 0;
crossCheckStateCount[1] = 0;
crossCheckStateCount[2] = 0;
crossCheckStateCount[3] = 0;
crossCheckStateCount[4] = 0;
return crossCheckStateCount;
}
}
/// <summary>
/// <p>After a horizontal scan finds a potential finder pattern, this method
/// "cross-checks" by scanning down vertically through the center of the possible
/// finder pattern to see if the same proportion is detected.</p>
/// </summary>
/// <param name="startI"> row where a finder pattern was detected </param>
/// <param name="centerJ"> center of the section that appears to cross a finder pattern </param>
/// <param name="maxCount"> maximum reasonable number of modules that should be
/// observed in any reading state, based on the results of the horizontal scan </param>
/// <returns> vertical center of finder pattern, or <seealso cref="Float#NaN"/> if not found </returns>
private float crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal)
{
BitMatrix image = this.image;
int maxI = image.Height;
int[] stateCount = CrossCheckStateCount;
// Start counting up from center
int i = startI;
while (i >= 0 && image.get(centerJ, i))
{
stateCount[2]++;
i--;
}
if (i < 0)
{
return float.NaN;
}
while (i >= 0 && !image.get(centerJ, i) && stateCount[1] <= maxCount)
{
stateCount[1]++;
i--;
}
// If already too many modules in this state or ran off the edge:
if (i < 0 || stateCount[1] > maxCount)
{
return float.NaN;
}
while (i >= 0 && image.get(centerJ, i) && stateCount[0] <= maxCount)
{
stateCount[0]++;
i--;
}
if (stateCount[0] > maxCount)
{
return float.NaN;
}
// Now also count down from center
i = startI + 1;
while (i < maxI && image.get(centerJ, i))
{
stateCount[2]++;
i++;
}
if (i == maxI)
{
return float.NaN;
}
while (i < maxI && !image.get(centerJ, i) && stateCount[3] < maxCount)
{
stateCount[3]++;
i++;
}
if (i == maxI || stateCount[3] >= maxCount)
{
return float.NaN;
}
while (i < maxI && image.get(centerJ, i) && stateCount[4] < maxCount)
{
stateCount[4]++;
i++;
}
if (stateCount[4] >= maxCount)
{
return float.NaN;
}
// If we found a finder-pattern-like section, but its size is more than 40% different than
// the original, assume it's a false positive
int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
if (5 * Math.Abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal)
{
return float.NaN;
}
return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : float.NaN;
}
/// <summary>
/// <p>Like <seealso cref="#crossCheckVertical(int, int, int, int)"/>, and in fact is basically identical,
/// except it reads horizontally instead of vertically. This is used to cross-cross
/// check a vertical cross check and locate the real center of the alignment pattern.</p>
/// </summary>
private float crossCheckHorizontal(int startJ, int centerI, int maxCount, int originalStateCountTotal)
{
BitMatrix image = this.image;
int maxJ = image.Width;
int[] stateCount = CrossCheckStateCount;
int j = startJ;
while (j >= 0 && image.get(j, centerI))
{
stateCount[2]++;
j--;
}
if (j < 0)
{
return float.NaN;
}
while (j >= 0 && !image.get(j, centerI) && stateCount[1] <= maxCount)
{
stateCount[1]++;
j--;
}
if (j < 0 || stateCount[1] > maxCount)
{
return float.NaN;
}
while (j >= 0 && image.get(j, centerI) && stateCount[0] <= maxCount)
{
stateCount[0]++;
j--;
}
if (stateCount[0] > maxCount)
{
return float.NaN;
}
j = startJ + 1;
while (j < maxJ && image.get(j, centerI))
{
stateCount[2]++;
j++;
}
if (j == maxJ)
{
return float.NaN;
}
while (j < maxJ && !image.get(j, centerI) && stateCount[3] < maxCount)
{
stateCount[3]++;
j++;
}
if (j == maxJ || stateCount[3] >= maxCount)
{
return float.NaN;
}
while (j < maxJ && image.get(j, centerI) && stateCount[4] < maxCount)
{
stateCount[4]++;
j++;
}
if (stateCount[4] >= maxCount)
{
return float.NaN;
}
// If we found a finder-pattern-like section, but its size is significantly different than
// the original, assume it's a false positive
int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
if (5 * Math.Abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal)
{
return float.NaN;
}
return foundPatternCross(stateCount) ? centerFromEnd(stateCount, j) : float.NaN;
}
/// <summary>
/// <p>This is called when a horizontal scan finds a possible alignment pattern. It will
/// cross check with a vertical scan, and if successful, will, ah, cross-cross-check
/// with another horizontal scan. This is needed primarily to locate the real horizontal
/// center of the pattern in cases of extreme skew.</p>
///
/// <p>If that succeeds the finder pattern location is added to a list that tracks
/// the number of times each location has been nearly-matched as a finder pattern.
/// Each additional find is more evidence that the location is in fact a finder
/// pattern center
/// </summary>
/// <param name="stateCount"> reading state module counts from horizontal scan </param>
/// <param name="i"> row where finder pattern may be found </param>
/// <param name="j"> end of possible finder pattern in row </param>
/// <returns> true if a finder pattern candidate was found this time </returns>
protected internal bool handlePossibleCenter(int[] stateCount, int i, int j)
{
int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
float centerJ = centerFromEnd(stateCount, j);
float centerI = crossCheckVertical(i, (int) centerJ, stateCount[2], stateCountTotal);
if (!float.IsNaN(centerI))
{
// Re-cross check
centerJ = crossCheckHorizontal((int) centerJ, (int) centerI, stateCount[2], stateCountTotal);
if (!float.IsNaN(centerJ))
{
float estimatedModuleSize = (float) stateCountTotal / 7.0f;
bool found = false;
for (int index = 0; index < possibleCenters.Count; index++)
{
FinderPattern center = possibleCenters[index];
// Look for about the same center and module size:
if (center.aboutEquals(estimatedModuleSize, centerI, centerJ))
{
possibleCenters[index] = center.combineEstimate(centerI, centerJ, estimatedModuleSize);
found = true;
break;
}
}
if (!found)
{
FinderPattern point = new FinderPattern(centerJ, centerI, estimatedModuleSize);
possibleCenters.Add(point);
if (resultPointCallback != null)
{
resultPointCallback.foundPossibleResultPoint(point);
}
}
return true;
}
}
return false;
}
/// <returns> number of rows we could safely skip during scanning, based on the first
/// two finder patterns that have been located. In some cases their position will
/// allow us to infer that the third pattern must lie below a certain point farther
/// down in the image. </returns>
private int findRowSkip()
{
int max = possibleCenters.Count;
if (max <= 1)
{
return 0;
}
FinderPattern firstConfirmedCenter = null;
foreach (FinderPattern center in possibleCenters)
{
if (center.Count >= CENTER_QUORUM)
{
if (firstConfirmedCenter == null)
{
firstConfirmedCenter = center;
}
else
{
// We have two confirmed centers
// How far down can we skip before resuming looking for the next
// pattern? In the worst case, only the difference between the
// difference in the x / y coordinates of the two centers.
// This is the case where you find top left last.
hasSkipped = true;
return (int)(Math.Abs(firstConfirmedCenter.X - center.X) - Math.Abs(firstConfirmedCenter.Y - center.Y)) / 2;
}
}
}
return 0;
}
/// <returns> true iff we have found at least 3 finder patterns that have been detected
/// at least <seealso cref="#CENTER_QUORUM"/> times each, and, the estimated module size of the
/// candidates is "pretty similar" </returns>
private bool haveMultiplyConfirmedCenters()
{
int confirmedCount = 0;
float totalModuleSize = 0.0f;
int max = possibleCenters.Count;
foreach (FinderPattern pattern in possibleCenters)
{
if (pattern.Count >= CENTER_QUORUM)
{
confirmedCount++;
totalModuleSize += pattern.EstimatedModuleSize;
}
}
if (confirmedCount < 3)
{
return false;
}
// OK, we have at least 3 confirmed centers, but, it's possible that one is a "false positive"
// and that we need to keep looking. We detect this by asking if the estimated module sizes
// vary too much. We arbitrarily say that when the total deviation from average exceeds
// 5% of the total module size estimates, it's too much.
float average = totalModuleSize / (float) max;
float totalDeviation = 0.0f;
foreach (FinderPattern pattern in possibleCenters)
{
totalDeviation += Math.Abs(pattern.EstimatedModuleSize - average);
}
return totalDeviation <= 0.05f * totalModuleSize;
}
/// <returns> the 3 best <seealso cref="FinderPattern"/>s from our list of candidates. The "best" are
/// those that have been detected at least <seealso cref="#CENTER_QUORUM"/> times, and whose module
/// size differs from the average among those patterns the least </returns>
/// <exception cref="NotFoundException"> if 3 such finder patterns do not exist </exception>
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in .NET:
//ORIGINAL LINE: private FinderPattern[] selectBestPatterns() throws com.google.zxing.NotFoundException
private FinderPattern[] selectBestPatterns()
{
int startSize = possibleCenters.Count;
if (startSize < 3)
{
// Couldn't find enough finder patterns
throw NotFoundException.NotFoundInstance;
}
// Filter outlier possibilities whose module size is too different
if (startSize > 3)
{
// But we can only afford to do so if we have at least 4 possibilities to choose from
float totalModuleSize = 0.0f;
float square = 0.0f;
foreach (FinderPattern center in possibleCenters)
{
float size = center.EstimatedModuleSize;
totalModuleSize += size;
square += size * size;
}
float average = totalModuleSize / (float) startSize;
float stdDev = (float) Math.Sqrt(square / startSize - average * average);
possibleCenters.Sort(new FurthestFromAverageComparator(average));
float limit = Math.Max(0.2f * average, stdDev);
for (int i = 0; i < possibleCenters.Count && possibleCenters.Count > 3; i++)
{
FinderPattern pattern = possibleCenters[i];
if (Math.Abs(pattern.EstimatedModuleSize - average) > limit)
{
possibleCenters.RemoveAt(i);
i--;
}
}
}
if (possibleCenters.Count > 3)
{
// Throw away all but those first size candidate points we found.
float totalModuleSize = 0.0f;
foreach (FinderPattern possibleCenter in possibleCenters)
{
totalModuleSize += possibleCenter.EstimatedModuleSize;
}
float average = totalModuleSize / (float) possibleCenters.Count;
possibleCenters.Sort(new CenterComparator(average));
//possibleCenters.subList(3, possibleCenters.Count).clear();
possibleCenters.RemoveRange(3,possibleCenters.Count-3);
}
return new FinderPattern[]{possibleCenters[0], possibleCenters[1], possibleCenters[2]};
}
/// <summary>
/// <p>Orders by furthest from average</p>
/// </summary>
[Serializable]
private sealed class FurthestFromAverageComparator : IComparer<FinderPattern>
{
private readonly float average;
internal FurthestFromAverageComparator(float f)
{
average = f;
}
public int Compare(FinderPattern center1, FinderPattern center2)
{
float dA = Math.Abs(center2.EstimatedModuleSize - average);
float dB = Math.Abs(center1.EstimatedModuleSize - average);
return dA < dB ? - 1 : dA == dB ? 0 : 1;
}
}
/// <summary>
/// <p>Orders by <seealso cref="FinderPattern#getCount()"/>, descending.</p>
/// </summary>
[Serializable]
private sealed class CenterComparator : IComparer<FinderPattern>
{
private readonly float average;
internal CenterComparator(float f)
{
average = f;
}
public int Compare(FinderPattern center1, FinderPattern center2)
{
if (center2.Count == center1.Count)
{
float dA = Math.Abs(center2.EstimatedModuleSize - average);
float dB = Math.Abs(center1.EstimatedModuleSize - average);
return dA < dB ? 1 : dA == dB ? 0 : -1;
}
else
{
return center2.Count - center1.Count;
}
}
}
}
}