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527 lines
23 KiB
C#
527 lines
23 KiB
C#
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/*
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* Copyright 2007 ZXing authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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namespace com.google.zxing.qrcode.detector
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{
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using System;
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using com.google.zxing;
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using com.google.zxing.common;
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public sealed class FinderPatternFinder
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{
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private static int CENTER_QUORUM = 2;
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private static int MIN_SKIP = 3; // 1 pixel/module times 3 modules/center
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private static int MAX_MODULES = 57; // support up to version 10 for mobile clients
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private static int INTEGER_MATH_SHIFT = 8;
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private MonochromeBitmapSource image;
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private System.Collections.ArrayList possibleCenters;
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private bool hasSkipped;
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private int[] crossCheckStateCount;
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/**
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* <p>Creates a finder that will search the image for three finder patterns.</p>
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*
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* @param image image to search
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*/
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public FinderPatternFinder(MonochromeBitmapSource image) {
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this.image = image;
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this.possibleCenters = new System.Collections.ArrayList();
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this.crossCheckStateCount = new int[5];
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}
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public FinderPatternInfo find(System.Collections.Hashtable hints) {
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bool tryHarder = hints != null && hints.ContainsKey(DecodeHintType.TRY_HARDER);
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int maxI = image.getHeight();
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int maxJ = image.getWidth();
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// We are looking for black/white/black/white/black modules in
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// 1:1:3:1:1 ratio; this tracks the number of such modules seen so far
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// Let's assume that the maximum version QR Code we support takes up 1/4 the height of the
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// image, and then account for the center being 3 modules in size. This gives the smallest
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// number of pixels the center could be, so skip this often. When trying harder, look for all
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// QR versions regardless of how dense they are.
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int iSkip = (int) (maxI / (MAX_MODULES * 4.0f) * 3);
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if (iSkip < MIN_SKIP || tryHarder) {
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iSkip = MIN_SKIP;
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}
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bool done = false;
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int[] stateCount = new int[5];
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BitArray blackRow = new BitArray(maxJ);
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for (int i = iSkip - 1; i < maxI && !done; i += iSkip) {
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// Get a row of black/white values
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blackRow = image.getBlackRow(i, blackRow, 0, maxJ);
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stateCount[0] = 0;
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stateCount[1] = 0;
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stateCount[2] = 0;
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stateCount[3] = 0;
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stateCount[4] = 0;
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int currentState = 0;
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for (int j = 0; j < maxJ; j++) {
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if (blackRow.get(j)) {
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// Black pixel
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if ((currentState & 1) == 1) { // Counting white pixels
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currentState++;
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}
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stateCount[currentState]++;
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} else { // White pixel
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if ((currentState & 1) == 0) { // Counting black pixels
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if (currentState == 4) { // A winner?
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if (foundPatternCross(stateCount)) { // Yes
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bool confirmed = handlePossibleCenter(stateCount, i, j);
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if (confirmed) {
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// Start examining every other line. Checking each line turned out to be too
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// expensive and didn't improve performance.
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iSkip = 2;
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if (hasSkipped) {
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done = haveMulitplyConfirmedCenters();
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} else {
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int rowSkip = findRowSkip();
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if (rowSkip > stateCount[2]) {
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// Skip rows between row of lower confirmed center
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// and top of presumed third confirmed center
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// but back up a bit to get a full chance of detecting
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// it, entire width of center of finder pattern
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// Skip by rowSkip, but back off by stateCount[2] (size of last center
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// of pattern we saw) to be conservative, and also back off by iSkip which
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// is about to be re-added
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i += rowSkip - stateCount[2] - iSkip;
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j = maxJ - 1;
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}
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}
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} else {
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// Advance to next black pixel
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do {
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j++;
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} while (j < maxJ && !blackRow.get(j));
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j--; // back up to that last white pixel
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}
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// Clear state to start looking again
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currentState = 0;
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stateCount[0] = 0;
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stateCount[1] = 0;
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stateCount[2] = 0;
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stateCount[3] = 0;
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stateCount[4] = 0;
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} else { // No, shift counts back by two
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stateCount[0] = stateCount[2];
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stateCount[1] = stateCount[3];
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stateCount[2] = stateCount[4];
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stateCount[3] = 1;
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stateCount[4] = 0;
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currentState = 3;
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}
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} else {
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stateCount[++currentState]++;
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}
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} else { // Counting white pixels
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stateCount[currentState]++;
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}
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}
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}
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if (foundPatternCross(stateCount)) {
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bool confirmed = handlePossibleCenter(stateCount, i, maxJ);
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if (confirmed) {
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iSkip = stateCount[0];
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if (hasSkipped) {
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// Found a third one
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done = haveMulitplyConfirmedCenters();
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}
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}
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}
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}
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FinderPattern[] patternInfo = selectBestPatterns();
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GenericResultPoint.orderBestPatterns(patternInfo);
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return new FinderPatternInfo(patternInfo);
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}
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/**
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* Given a count of black/white/black/white/black pixels just seen and an end position,
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* figures the location of the center of this run.
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*/
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private static float centerFromEnd(int[] stateCount, int end) {
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return (float) (end - stateCount[4] - stateCount[3]) - stateCount[2] / 2.0f;
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}
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/**
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* @param stateCount count of black/white/black/white/black pixels just read
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* @return true iff the proportions of the counts is close enough to the 1/1/3/1/1 ratios
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* used by finder patterns to be considered a match
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*/
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private static bool foundPatternCross(int[] stateCount) {
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int totalModuleSize = 0;
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for (int i = 0; i < 5; i++) {
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int count = stateCount[i];
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if (count == 0) {
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return false;
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}
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totalModuleSize += count;
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}
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if (totalModuleSize < 7) {
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return false;
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}
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int moduleSize = (totalModuleSize << INTEGER_MATH_SHIFT) / 7;
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int maxVariance = moduleSize / 2;
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// Allow less than 50% variance from 1-1-3-1-1 proportions
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return Math.Abs(moduleSize - (stateCount[0] << INTEGER_MATH_SHIFT)) < maxVariance &&
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Math.Abs(moduleSize - (stateCount[1] << INTEGER_MATH_SHIFT)) < maxVariance &&
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Math.Abs(3 * moduleSize - (stateCount[2] << INTEGER_MATH_SHIFT)) < 3 * maxVariance &&
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Math.Abs(moduleSize - (stateCount[3] << INTEGER_MATH_SHIFT)) < maxVariance &&
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Math.Abs(moduleSize - (stateCount[4] << INTEGER_MATH_SHIFT)) < maxVariance;
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}
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private int[] getCrossCheckStateCount() {
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crossCheckStateCount[0] = 0;
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crossCheckStateCount[1] = 0;
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crossCheckStateCount[2] = 0;
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crossCheckStateCount[3] = 0;
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crossCheckStateCount[4] = 0;
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return crossCheckStateCount;
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}
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/**
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* <p>After a horizontal scan finds a potential finder pattern, this method
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* "cross-checks" by scanning down vertically through the center of the possible
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* finder pattern to see if the same proportion is detected.</p>
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*
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* @param startI row where a finder pattern was detected
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* @param centerJ center of the section that appears to cross a finder pattern
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* @param maxCount maximum reasonable number of modules that should be
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* observed in any reading state, based on the results of the horizontal scan
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* @return vertical center of finder pattern, or {@link Float#NaN} if not found
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*/
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private float crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal) {
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MonochromeBitmapSource image = this.image;
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int maxI = image.getHeight();
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int[] stateCount = getCrossCheckStateCount();
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// Start counting up from center
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int i = startI;
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while (i >= 0 && image.isBlack(centerJ, i)) {
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stateCount[2]++;
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i--;
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}
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if (i < 0) {
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return float.NaN;
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}
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while (i >= 0 && !image.isBlack(centerJ, i) && stateCount[1] <= maxCount) {
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stateCount[1]++;
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i--;
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}
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// If already too many modules in this state or ran off the edge:
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if (i < 0 || stateCount[1] > maxCount) {
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return float.NaN;
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}
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while (i >= 0 && image.isBlack(centerJ, i) && stateCount[0] <= maxCount) {
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stateCount[0]++;
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i--;
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}
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if (stateCount[0] > maxCount) {
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return float.NaN;
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}
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// Now also count down from center
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i = startI + 1;
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while (i < maxI && image.isBlack(centerJ, i)) {
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stateCount[2]++;
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i++;
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}
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if (i == maxI) {
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return float.NaN;
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}
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while (i < maxI && !image.isBlack(centerJ, i) && stateCount[3] < maxCount) {
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stateCount[3]++;
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i++;
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}
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if (i == maxI || stateCount[3] >= maxCount) {
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return float.NaN;
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}
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while (i < maxI && image.isBlack(centerJ, i) && stateCount[4] < maxCount) {
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stateCount[4]++;
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i++;
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}
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if (stateCount[4] >= maxCount) {
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return float.NaN;
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}
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// If we found a finder-pattern-like section, but its size is more than 20% different than
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// the original, assume it's a false positive
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int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
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if (5 * Math.Abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal) {
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return float.NaN;
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}
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return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : float.NaN;
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}
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/**
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* <p>Like {@link #crossCheckVertical(int, int, int, int)}, and in fact is basically identical,
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* except it reads horizontally instead of vertically. This is used to cross-cross
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* check a vertical cross check and locate the real center of the alignment pattern.</p>
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*/
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private float crossCheckHorizontal(int startJ, int centerI, int maxCount, int originalStateCountTotal) {
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MonochromeBitmapSource image = this.image;
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int maxJ = image.getWidth();
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int[] stateCount = getCrossCheckStateCount();
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int j = startJ;
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while (j >= 0 && image.isBlack(j, centerI)) {
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stateCount[2]++;
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j--;
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}
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if (j < 0) {
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return float.NaN;
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}
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while (j >= 0 && !image.isBlack(j, centerI) && stateCount[1] <= maxCount) {
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stateCount[1]++;
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j--;
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}
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if (j < 0 || stateCount[1] > maxCount) {
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return float.NaN;
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}
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while (j >= 0 && image.isBlack(j, centerI) && stateCount[0] <= maxCount) {
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stateCount[0]++;
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j--;
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}
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if (stateCount[0] > maxCount) {
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return float.NaN;
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}
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j = startJ + 1;
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while (j < maxJ && image.isBlack(j, centerI)) {
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stateCount[2]++;
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j++;
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}
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if (j == maxJ) {
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return float.NaN;
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}
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while (j < maxJ && !image.isBlack(j, centerI) && stateCount[3] < maxCount) {
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stateCount[3]++;
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j++;
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}
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if (j == maxJ || stateCount[3] >= maxCount) {
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return float.NaN;
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}
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while (j < maxJ && image.isBlack(j, centerI) && stateCount[4] < maxCount) {
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stateCount[4]++;
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j++;
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}
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if (stateCount[4] >= maxCount) {
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return float.NaN;
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}
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// If we found a finder-pattern-like section, but its size is significantly different than
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// the original, assume it's a false positive
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int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
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if (5 * Math.Abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal) {
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return float.NaN;
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}
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return foundPatternCross(stateCount) ? centerFromEnd(stateCount, j) : float.NaN;
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}
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/**
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* <p>This is called when a horizontal scan finds a possible alignment pattern. It will
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* cross check with a vertical scan, and if successful, will, ah, cross-cross-check
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* with another horizontal scan. This is needed primarily to locate the real horizontal
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|
|
* 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
|
|||
|
|
*
|
|||
|
|
* @param stateCount reading state module counts from horizontal scan
|
|||
|
|
* @param i row where finder pattern may be found
|
|||
|
|
* @param j end of possible finder pattern in row
|
|||
|
|
* @return true if a finder pattern candidate was found this time
|
|||
|
|
*/
|
|||
|
|
private 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 (!Single.IsNaN(centerI)) {
|
|||
|
|
// Re-cross check
|
|||
|
|
centerJ = crossCheckHorizontal((int) centerJ, (int) centerI, stateCount[2], stateCountTotal);
|
|||
|
|
if (!Single.IsNaN(centerJ))
|
|||
|
|
{
|
|||
|
|
float estimatedModuleSize = (float) stateCountTotal / 7.0f;
|
|||
|
|
bool found = false;
|
|||
|
|
int max = possibleCenters.Count;
|
|||
|
|
for (int index = 0; index < max; index++) {
|
|||
|
|
FinderPattern center = (FinderPattern) possibleCenters[index];
|
|||
|
|
// Look for about the same center and module size:
|
|||
|
|
if (center.aboutEquals(estimatedModuleSize, centerI, centerJ)) {
|
|||
|
|
center.incrementCount();
|
|||
|
|
found = true;
|
|||
|
|
break;
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
if (!found) {
|
|||
|
|
possibleCenters.Add(new FinderPattern(centerJ, centerI, estimatedModuleSize));
|
|||
|
|
}
|
|||
|
|
return true;
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
return false;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/**
|
|||
|
|
* @return 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.
|
|||
|
|
*/
|
|||
|
|
private int findRowSkip() {
|
|||
|
|
int max = possibleCenters.Count;
|
|||
|
|
if (max <= 1) {
|
|||
|
|
return 0;
|
|||
|
|
}
|
|||
|
|
FinderPattern firstConfirmedCenter = null;
|
|||
|
|
for (int i = 0; i < max; i++) {
|
|||
|
|
FinderPattern center = (FinderPattern) possibleCenters[i];
|
|||
|
|
if (center.getCount() >= 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 first. Draw it out.
|
|||
|
|
hasSkipped = true;
|
|||
|
|
return (int) (Math.Abs(firstConfirmedCenter.getX() - center.getX()) -
|
|||
|
|
Math.Abs(firstConfirmedCenter.getY() - center.getY()));
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
return 0;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/**
|
|||
|
|
* @return true iff we have found at least 3 finder patterns that have been detected
|
|||
|
|
* at least {@link #CENTER_QUORUM} times each, and, the estimated module size of the
|
|||
|
|
* candidates is "pretty similar"
|
|||
|
|
*/
|
|||
|
|
private bool haveMulitplyConfirmedCenters() {
|
|||
|
|
int confirmedCount = 0;
|
|||
|
|
float totalModuleSize = 0.0f;
|
|||
|
|
int max = possibleCenters.Count;
|
|||
|
|
for (int i = 0; i < max; i++) {
|
|||
|
|
FinderPattern pattern = (FinderPattern) possibleCenters[i];
|
|||
|
|
if (pattern.getCount() >= CENTER_QUORUM) {
|
|||
|
|
confirmedCount++;
|
|||
|
|
totalModuleSize += pattern.getEstimatedModuleSize();
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
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
|
|||
|
|
// 15% of the total module size estimates, it's too much.
|
|||
|
|
float average = totalModuleSize / max;
|
|||
|
|
float totalDeviation = 0.0f;
|
|||
|
|
for (int i = 0; i < max; i++) {
|
|||
|
|
FinderPattern pattern = (FinderPattern) possibleCenters[i];
|
|||
|
|
totalDeviation += Math.Abs(pattern.getEstimatedModuleSize() - average);
|
|||
|
|
}
|
|||
|
|
return totalDeviation <= 0.15f * totalModuleSize;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/**
|
|||
|
|
* @return the 3 best {@link FinderPattern}s from our list of candidates. The "best" are
|
|||
|
|
* those that have been detected at least {@link #CENTER_QUORUM} times, and whose module
|
|||
|
|
* size differs from the average among those patterns the least
|
|||
|
|
* @throws ReaderException if 3 such finder patterns do not exist
|
|||
|
|
*/
|
|||
|
|
private FinderPattern[] selectBestPatterns(){
|
|||
|
|
Collections.insertionSort(possibleCenters, new CenterComparator());
|
|||
|
|
int size = 0;
|
|||
|
|
int max = possibleCenters.Count;
|
|||
|
|
while (size < max) {
|
|||
|
|
if (((FinderPattern) possibleCenters[size]).getCount() < CENTER_QUORUM) {
|
|||
|
|
break;
|
|||
|
|
}
|
|||
|
|
size++;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
if (size < 3) {
|
|||
|
|
// Couldn't find enough finder patterns
|
|||
|
|
throw new ReaderException();
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
if (size > 3) {
|
|||
|
|
// Throw away all but those first size candidate points we found.
|
|||
|
|
SupportClass.SetCapacity(possibleCenters, size);
|
|||
|
|
// We need to pick the best three. Find the most
|
|||
|
|
// popular ones whose module size is nearest the average
|
|||
|
|
float averageModuleSize = 0.0f;
|
|||
|
|
for (int i = 0; i < size; i++) {
|
|||
|
|
averageModuleSize += ((FinderPattern) possibleCenters[i]).getEstimatedModuleSize();
|
|||
|
|
}
|
|||
|
|
averageModuleSize /= (float) size;
|
|||
|
|
// We don't have java.util.Collections in J2ME
|
|||
|
|
Collections.insertionSort(possibleCenters, new ClosestToAverageComparator(averageModuleSize));
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
return new FinderPattern[]{
|
|||
|
|
(FinderPattern) possibleCenters[0],
|
|||
|
|
(FinderPattern) possibleCenters[1],
|
|||
|
|
(FinderPattern) possibleCenters[2]
|
|||
|
|
};
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/**
|
|||
|
|
* <p>Orders by {@link FinderPattern#getCount()}, descending.</p>
|
|||
|
|
*/
|
|||
|
|
private class CenterComparator : Comparator {
|
|||
|
|
public int compare(object center1, object center2)
|
|||
|
|
{
|
|||
|
|
return ((FinderPattern) center2).getCount() - ((FinderPattern) center1).getCount();
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
/**
|
|||
|
|
* <p>Orders by variance from average module size, ascending.</p>
|
|||
|
|
*/
|
|||
|
|
private class ClosestToAverageComparator : Comparator {
|
|||
|
|
private float averageModuleSize;
|
|||
|
|
|
|||
|
|
public ClosestToAverageComparator(float averageModuleSize) {
|
|||
|
|
this.averageModuleSize = averageModuleSize;
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
public int compare(object center1, object center2)
|
|||
|
|
{
|
|||
|
|
return Math.Abs(((FinderPattern) center1).getEstimatedModuleSize() - averageModuleSize) <
|
|||
|
|
Math.Abs(((FinderPattern) center2).getEstimatedModuleSize() - averageModuleSize) ?
|
|||
|
|
-1 :
|
|||
|
|
1;
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
}
|