2 * Copyright 2008 ZXing authors
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 package com.google.zxing.oned;
19 import com.google.zxing.BinaryBitmap;
20 import com.google.zxing.DecodeHintType;
21 import com.google.zxing.ReaderException;
22 import com.google.zxing.Result;
23 import com.google.zxing.ResultMetadataType;
24 import com.google.zxing.ResultPoint;
25 import com.google.zxing.common.BitArray;
27 import java.util.Hashtable;
30 * <p>Encapsulates functionality and implementation that is common to all families
31 * of one-dimensional barcodes.</p>
33 * @author dswitkin@google.com (Daniel Switkin)
36 public abstract class AbstractOneDReader implements OneDReader {
38 private static final int INTEGER_MATH_SHIFT = 8;
39 static final int PATTERN_MATCH_RESULT_SCALE_FACTOR = 1 << INTEGER_MATH_SHIFT;
41 public final Result decode(BinaryBitmap image) throws ReaderException {
42 return decode(image, null);
45 public final Result decode(BinaryBitmap image, Hashtable hints) throws ReaderException {
47 return doDecode(image, hints);
48 } catch (ReaderException re) {
49 boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
50 if (tryHarder && image.isRotateSupported()) {
51 BinaryBitmap rotatedImage = image.rotateCounterClockwise();
52 Result result = doDecode(rotatedImage, hints);
53 // Record that we found it rotated 90 degrees CCW / 270 degrees CW
54 Hashtable metadata = result.getResultMetadata();
55 int orientation = 270;
56 if (metadata != null && metadata.containsKey(ResultMetadataType.ORIENTATION)) {
57 // But if we found it reversed in doDecode(), add in that result here:
58 orientation = (orientation +
59 ((Integer) metadata.get(ResultMetadataType.ORIENTATION)).intValue()) % 360;
61 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(orientation));
70 * We're going to examine rows from the middle outward, searching alternately above and below the
71 * middle, and farther out each time. rowStep is the number of rows between each successive
72 * attempt above and below the middle. So we'd scan row middle, then middle - rowStep, then
73 * middle + rowStep, then middle - (2 * rowStep), etc.
74 * rowStep is bigger as the image is taller, but is always at least 1. We've somewhat arbitrarily
75 * decided that moving up and down by about 1/16 of the image is pretty good; we try more of the
76 * image if "trying harder".
78 * @param image The image to decode
79 * @param hints Any hints that were requested
80 * @return The contents of the decoded barcode
81 * @throws ReaderException Any spontaneous errors which occur
83 private Result doDecode(BinaryBitmap image, Hashtable hints) throws ReaderException {
84 int width = image.getWidth();
85 int height = image.getHeight();
86 BitArray row = new BitArray(width);
88 int middle = height >> 1;
89 boolean tryHarder = hints != null && hints.containsKey(DecodeHintType.TRY_HARDER);
90 int rowStep = Math.max(1, height >> (tryHarder ? 7 : 4));
93 maxLines = height; // Look at the whole image, not just the center
95 maxLines = 9; // Nine rows spaced 1/16 apart is roughly the middle half of the image
98 for (int x = 0; x < maxLines; x++) {
100 // Scanning from the middle out. Determine which row we're looking at next:
101 int rowStepsAboveOrBelow = (x + 1) >> 1;
102 boolean isAbove = (x & 0x01) == 0; // i.e. is x even?
103 int rowNumber = middle + rowStep * (isAbove ? rowStepsAboveOrBelow : -rowStepsAboveOrBelow);
104 if (rowNumber < 0 || rowNumber >= height) {
105 // Oops, if we run off the top or bottom, stop
109 // Estimate black point for this row and load it:
111 row = image.getBlackRow(rowNumber, row);
112 } catch (ReaderException re) {
116 // While we have the image data in a BitArray, it's fairly cheap to reverse it in place to
117 // handle decoding upside down barcodes.
118 for (int attempt = 0; attempt < 2; attempt++) {
119 if (attempt == 1) { // trying again?
120 row.reverse(); // reverse the row and continue
123 // Look for a barcode
124 Result result = decodeRow(rowNumber, row, hints);
125 // We found our barcode
127 // But it was upside down, so note that
128 result.putMetadata(ResultMetadataType.ORIENTATION, new Integer(180));
129 // And remember to flip the result points horizontally.
130 ResultPoint[] points = result.getResultPoints();
131 points[0] = new ResultPoint(width - points[0].getX() - 1, points[0].getY());
132 points[1] = new ResultPoint(width - points[1].getX() - 1, points[1].getY());
135 } catch (ReaderException re) {
136 // continue -- just couldn't decode this row
141 throw ReaderException.getInstance();
145 * Records the size of successive runs of white and black pixels in a row, starting at a given point.
146 * The values are recorded in the given array, and the number of runs recorded is equal to the size
147 * of the array. If the row starts on a white pixel at the given start point, then the first count
148 * recorded is the run of white pixels starting from that point; likewise it is the count of a run
149 * of black pixels if the row begin on a black pixels at that point.
151 * @param row row to count from
152 * @param start offset into row to start at
153 * @param counters array into which to record counts
154 * @throws ReaderException if counters cannot be filled entirely from row before running out
157 static void recordPattern(BitArray row, int start, int[] counters) throws ReaderException {
158 int numCounters = counters.length;
159 for (int i = 0; i < numCounters; i++) {
162 int end = row.getSize();
164 throw ReaderException.getInstance();
166 boolean isWhite = !row.get(start);
167 int counterPosition = 0;
170 boolean pixel = row.get(i);
171 if (pixel ^ isWhite) { // that is, exactly one is true
172 counters[counterPosition]++;
175 if (counterPosition == numCounters) {
178 counters[counterPosition] = 1;
179 isWhite ^= true; // isWhite = !isWhite; Is this too clever? shorter byte code, no conditional
184 // If we read fully the last section of pixels and filled up our counters -- or filled
185 // the last counter but ran off the side of the image, OK. Otherwise, a problem.
186 if (!(counterPosition == numCounters || (counterPosition == numCounters - 1 && i == end))) {
187 throw ReaderException.getInstance();
192 * Determines how closely a set of observed counts of runs of black/white values matches a given
193 * target pattern. This is reported as the ratio of the total variance from the expected pattern
194 * proportions across all pattern elements, to the length of the pattern.
196 * @param counters observed counters
197 * @param pattern expected pattern
198 * @param maxIndividualVariance The most any counter can differ before we give up
199 * @return ratio of total variance between counters and pattern compared to total pattern size,
200 * where the ratio has been multiplied by 256. So, 0 means no variance (perfect match); 256 means
201 * the total variance between counters and patterns equals the pattern length, higher values mean
204 static int patternMatchVariance(int[] counters, int[] pattern, int maxIndividualVariance) {
205 int numCounters = counters.length;
207 int patternLength = 0;
208 for (int i = 0; i < numCounters; i++) {
209 total += counters[i];
210 patternLength += pattern[i];
212 if (total < patternLength) {
213 // If we don't even have one pixel per unit of bar width, assume this is too small
214 // to reliably match, so fail:
215 return Integer.MAX_VALUE;
217 // We're going to fake floating-point math in integers. We just need to use more bits.
218 // Scale up patternLength so that intermediate values below like scaledCounter will have
219 // more "significant digits"
220 int unitBarWidth = (total << INTEGER_MATH_SHIFT) / patternLength;
221 maxIndividualVariance = (maxIndividualVariance * unitBarWidth) >> INTEGER_MATH_SHIFT;
223 int totalVariance = 0;
224 for (int x = 0; x < numCounters; x++) {
225 int counter = counters[x] << INTEGER_MATH_SHIFT;
226 int scaledPattern = pattern[x] * unitBarWidth;
227 int variance = counter > scaledPattern ? counter - scaledPattern : scaledPattern - counter;
228 if (variance > maxIndividualVariance) {
229 return Integer.MAX_VALUE;
231 totalVariance += variance;
233 return totalVariance / total;
236 // This declaration should not be necessary, since this class is
237 // abstract and so does not have to provide an implementation for every
238 // method of an interface it implements, but it is causing NoSuchMethodError
239 // issues on some Nokia JVMs. So we add this superfluous declaration:
241 public abstract Result decodeRow(int rowNumber, BitArray row, Hashtable hints)
242 throws ReaderException;