2 * Copyright 2007 ZXing authors
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4 * Licensed under the Apache License, Version 2.0 (the "License");
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5 * you may not use this file except in compliance with the License.
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6 * You may obtain a copy of the License at
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8 * http://www.apache.org/licenses/LICENSE-2.0
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10 * Unless required by applicable law or agreed to in writing, software
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11 * distributed under the License is distributed on an "AS IS" BASIS,
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12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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13 * See the License for the specific language governing permissions and
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14 * limitations under the License.
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16 namespace com.google.zxing.oned
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19 using com.google.zxing.common;
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21 public abstract class AbstractOneDReader
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23 private static int INTEGER_MATH_SHIFT = 8;
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24 public static int PATTERN_MATCH_RESULT_SCALE_FACTOR = 1 << INTEGER_MATH_SHIFT;
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26 public Result decode(MonochromeBitmapSource image) {
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27 return decode(image, null);
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30 public Result decode(MonochromeBitmapSource image, System.Collections.Hashtable hints) {
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32 return doDecode(image, hints);
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33 } catch (ReaderException re) {
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34 bool tryHarder = hints != null && hints.ContainsKey(DecodeHintType.TRY_HARDER);
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35 if (tryHarder && image.isRotateSupported()) {
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36 MonochromeBitmapSource rotatedImage = image.rotateCounterClockwise();
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37 Result result = doDecode(rotatedImage, hints);
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38 // Record that we found it rotated 90 degrees CCW / 270 degrees CW
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39 System.Collections.Hashtable metadata = result.getResultMetadata();
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40 int orientation = 270;
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41 if (metadata != null && metadata.ContainsKey(ResultMetadataType.ORIENTATION)) {
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42 // But if we found it reversed in doDecode(), add in that result here:
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43 orientation = (orientation + ((int) metadata[ResultMetadataType.ORIENTATION])) % 360;
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45 result.putMetadata(ResultMetadataType.ORIENTATION, orientation);
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54 * We're going to examine rows from the middle outward, searching alternately above and below the
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55 * middle, and farther out each time. rowStep is the number of rows between each successive
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56 * attempt above and below the middle. So we'd scan row middle, then middle - rowStep, then
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57 * middle + rowStep, then middle - (2 * rowStep), etc.
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58 * rowStep is bigger as the image is taller, but is always at least 1. We've somewhat arbitrarily
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59 * decided that moving up and down by about 1/16 of the image is pretty good; we try more of the
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60 * image if "trying harder".
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62 * @param image The image to decode
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63 * @param hints Any hints that were requested
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64 * @return The contents of the decoded barcode
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65 * @throws ReaderException Any spontaneous errors which occur
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67 private Result doDecode(MonochromeBitmapSource image, System.Collections.Hashtable hints) {
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68 int width = image.getWidth();
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69 int height = image.getHeight();
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70 BitArray row = new BitArray(width);
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72 int middle = height >> 1;
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73 bool tryHarder = hints != null && hints.ContainsKey(DecodeHintType.TRY_HARDER);
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74 int rowStep = Math.Max(1, height >> (tryHarder ? 7 : 4));
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77 MaxLines = height; // Look at the whole image, not just the center
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79 MaxLines = 9; // Nine rows spaced 1/16 apart is roughly the middle half of the image
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82 for (int x = 0; x < MaxLines; x++) {
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84 // Scanning from the middle out. Determine which row we're looking at next:
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85 int rowStepsAboveOrBelow = (x + 1) >> 1;
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86 bool isAbove = (x & 0x01) == 0; // i.e. is x even?
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87 int rowNumber = middle + rowStep * (isAbove ? rowStepsAboveOrBelow : -rowStepsAboveOrBelow);
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88 if (rowNumber < 0 || rowNumber >= height) {
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89 // Oops, if we run off the top or bottom, stop
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93 // Estimate black point for this row and load it:
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95 image.estimateBlackPoint(BlackPointEstimationMethod.ROW_SAMPLING, rowNumber);
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96 } catch (ReaderException re) {
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100 image.getBlackRow(rowNumber, row,0, width);
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102 // While we have the image data in a BitArray, it's fairly cheap to reverse it in place to
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103 // handle decoding upside down barcodes.
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104 for (int attempt = 0; attempt < 2; attempt++) {
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105 if (attempt == 1) { // trying again?
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106 row.reverse(); // reverse the row and continue
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109 // Look for a barcode
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110 Result result = decodeRow(rowNumber, row, hints);
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111 // We found our barcode
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112 if (attempt == 1) {
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113 // But it was upside down, so note that
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114 result.putMetadata(ResultMetadataType.ORIENTATION, 180);
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115 // And remember to flip the result points horizontally.
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116 ResultPoint[] points = result.getResultPoints();
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117 points[0] = (ResultPoint) new GenericResultPoint(width - points[0].getX() - 1, points[0].getY());
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118 points[1] = (ResultPoint)new GenericResultPoint(width - points[1].getX() - 1, points[1].getY());
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121 } catch (ReaderException re) {
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122 // continue -- just couldn't decode this row
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127 throw new ReaderException();
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131 * Records the size of successive runs of white and black pixels in a row, starting at a given point.
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132 * The values are recorded in the given array, and the number of runs recorded is equal to the size
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133 * of the array. If the row starts on a white pixel at the given start point, then the first count
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134 * recorded is the run of white pixels starting from that point; likewise it is the count of a run
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135 * of black pixels if the row begin on a black pixels at that point.
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137 * @param row row to count from
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138 * @param start offset into row to start at
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139 * @param counters array into which to record counts
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140 * @throws ReaderException if counters cannot be filled entirely from row before running out of pixels
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142 public static void recordPattern(BitArray row, int start, int[] counters) {
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143 int numCounters = counters.Length;
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144 for (int i = 0; i < numCounters; i++) {
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147 int end = row.getSize();
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148 if (start >= end) {
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149 throw new ReaderException();
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151 bool isWhite = !row.get(start);
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152 int counterPosition = 0;
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156 bool pixel = row.get(k);
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157 if ((!pixel && isWhite) || (pixel && !isWhite)) {
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158 counters[counterPosition]++;
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161 if (counterPosition == numCounters) {
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164 counters[counterPosition] = 1;
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165 isWhite = !isWhite;
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170 // If we read fully the last section of pixels and filled up our counters -- or filled
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171 // the last counter but ran off the side of the image, OK. Otherwise, a problem.
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172 if (!(counterPosition == numCounters || (counterPosition == numCounters - 1 && k == end))) {
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173 throw new ReaderException();
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178 * Determines how closely a set of observed counts of runs of black/white values matches a given
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179 * target pattern. This is reported as the ratio of the total variance from the expected pattern
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180 * proportions across all pattern elements, to the length of the pattern.
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182 * @param counters observed counters
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183 * @param pattern expected pattern
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184 * @param MaxIndividualVariance The most any counter can differ before we give up
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185 * @return ratio of total variance between counters and pattern compared to total pattern size,
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186 * where the ratio has been multiplied by 256. So, 0 means no variance (perfect match); 256 means
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187 * the total variance between counters and patterns equals the pattern length, higher values mean
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188 * even more variance
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190 public static int patternMatchVariance(int[] counters, int[] pattern, int MaxIndividualVariance) {
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191 int numCounters = counters.Length;
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193 int patternLength = 0;
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194 for (int i = 0; i < numCounters; i++) {
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195 total += counters[i];
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196 patternLength += pattern[i];
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198 if (total < patternLength) {
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199 // If we don't even have one pixel per unit of bar width, assume this is too small
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200 // to reliably match, so fail:
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201 return int.MaxValue;
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203 // We're going to fake floating-point math in integers. We just need to use more bits.
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204 // Scale up patternLength so that intermediate values below like scaledCounter will have
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205 // more "significant digits"
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206 int unitBarWidth = (total << INTEGER_MATH_SHIFT) / patternLength;
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207 MaxIndividualVariance = (MaxIndividualVariance * unitBarWidth) >> INTEGER_MATH_SHIFT;
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209 int totalVariance = 0;
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210 for (int x = 0; x < numCounters; x++) {
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211 int counter = counters[x] << INTEGER_MATH_SHIFT;
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212 int scaledPattern = pattern[x] * unitBarWidth;
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213 int variance = counter > scaledPattern ? counter - scaledPattern : scaledPattern - counter;
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214 if (variance > MaxIndividualVariance) {
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215 return int.MaxValue;
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217 totalVariance += variance;
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219 return totalVariance / total;
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222 // This declaration should not be necessary, since this class is
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223 // abstract and so does not have to provide an implementation for every
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224 // method of an interface it implements, but it is causing NoSuchMethodError
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225 // issues on some Nokia JVMs. So we add this superfluous declaration:
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227 public abstract Result decodeRow(int rowNumber, BitArray row, System.Collections.Hashtable hints);
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