CodaBarReader.java

/*
 * 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.
 */

package com.google.zxing.oned;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.DecodeHintType;
import com.google.zxing.NotFoundException;
import com.google.zxing.Result;
import com.google.zxing.ResultPoint;
import com.google.zxing.common.BitArray;

import java.util.Map;

/**
 * <p>Decodes Codabar barcodes.</p>
 *
 * @author Bas Vijfwinkel
 * @author David Walker
 */
public final class CodaBarReader extends OneDReader {

  // These values are critical for determining how permissive the decoding
  // will be. All stripe sizes must be within the window these define, as
  // compared to the average stripe size.
  private static final int MAX_ACCEPTABLE = (int) (PATTERN_MATCH_RESULT_SCALE_FACTOR * 2.0f);
  private static final int PADDING = (int) (PATTERN_MATCH_RESULT_SCALE_FACTOR * 1.5f);

  private static final String ALPHABET_STRING = "0123456789-$:/.+ABCD";
  static final char[] ALPHABET = ALPHABET_STRING.toCharArray();

  /**
   * These represent the encodings of characters, as patterns of wide and narrow bars. The 7 least-significant bits of
   * each int correspond to the pattern of wide and narrow, with 1s representing "wide" and 0s representing narrow.
   */
  static final int[] CHARACTER_ENCODINGS = {
      0x003, 0x006, 0x009, 0x060, 0x012, 0x042, 0x021, 0x024, 0x030, 0x048, // 0-9
      0x00c, 0x018, 0x045, 0x051, 0x054, 0x015, 0x01A, 0x029, 0x00B, 0x00E, // -$:/.+ABCD
  };

  // minimal number of characters that should be present (inclusing start and stop characters)
  // under normal circumstances this should be set to 3, but can be set higher
  // as a last-ditch attempt to reduce false positives.
  private static final int MIN_CHARACTER_LENGTH = 3;

  // official start and end patterns
  private static final char[] STARTEND_ENCODING = {'A', 'B', 'C', 'D'};
  // some codabar generator allow the codabar string to be closed by every
  // character. This will cause lots of false positives!

  // some industries use a checksum standard but this is not part of the original codabar standard
  // for more information see : http://www.mecsw.com/specs/codabar.html

  // Keep some instance variables to avoid reallocations
  private final StringBuilder decodeRowResult;
  private int[] counters;
  private int counterLength;

  public CodaBarReader() {
    decodeRowResult = new StringBuilder(20);
    counters = new int[80];
    counterLength = 0;
  }

  @Override
  public Result decodeRow(int rowNumber, BitArray row, Map<DecodeHintType,?> hints) throws NotFoundException {

    setCounters(row);
    int startOffset = findStartPattern();
    int nextStart = startOffset;

    decodeRowResult.setLength(0);
    do {
      int charOffset = toNarrowWidePattern(nextStart);
      if (charOffset == -1) {
        throw NotFoundException.getNotFoundInstance();
      }
      // Hack: We store the position in the alphabet table into a
      // StringBuilder, so that we can access the decoded patterns in
      // validatePattern. We'll translate to the actual characters later.
      decodeRowResult.append((char)charOffset);
      nextStart += 8;
      // Stop as soon as we see the end character.
      if (decodeRowResult.length() > 1 &&
          arrayContains(STARTEND_ENCODING, ALPHABET[charOffset])) {
        break;
      }
    } while (nextStart < counterLength); // no fixed end pattern so keep on reading while data is available

    // Look for whitespace after pattern:
    int trailingWhitespace = counters[nextStart - 1];
    int lastPatternSize = 0;
    for (int i = -8; i < -1; i++) {
      lastPatternSize += counters[nextStart + i];
    }

    // We need to see whitespace equal to 50% of the last pattern size,
    // otherwise this is probably a false positive. The exception is if we are
    // at the end of the row. (I.e. the barcode barely fits.)
    if (nextStart < counterLength && trailingWhitespace < lastPatternSize / 2) {
      throw NotFoundException.getNotFoundInstance();
    }

    validatePattern(startOffset);

    // Translate character table offsets to actual characters.
    for (int i = 0; i < decodeRowResult.length(); i++) {
      decodeRowResult.setCharAt(i, ALPHABET[decodeRowResult.charAt(i)]);
    }
    // Ensure a valid start and end character
    char startchar = decodeRowResult.charAt(0);
    if (!arrayContains(STARTEND_ENCODING, startchar)) {
      throw NotFoundException.getNotFoundInstance();
    }
    char endchar = decodeRowResult.charAt(decodeRowResult.length() - 1);
    if (!arrayContains(STARTEND_ENCODING, endchar)) {
      throw NotFoundException.getNotFoundInstance();
    }

    // remove stop/start characters character and check if a long enough string is contained
    if (decodeRowResult.length() <= MIN_CHARACTER_LENGTH) {
      // Almost surely a false positive ( start + stop + at least 1 character)
      throw NotFoundException.getNotFoundInstance();
    }

    decodeRowResult.deleteCharAt(decodeRowResult.length() - 1);
    decodeRowResult.deleteCharAt(0);

    int runningCount = 0;
    for (int i = 0; i < startOffset; i++) {
      runningCount += counters[i];
    }
    float left = (float) runningCount;
    for (int i = startOffset; i < nextStart - 1; i++) {
      runningCount += counters[i];
    }
    float right = (float) runningCount;
    return new Result(
        decodeRowResult.toString(),
        null,
        new ResultPoint[]{
            new ResultPoint(left, (float) rowNumber),
            new ResultPoint(right, (float) rowNumber)},
        BarcodeFormat.CODABAR);
  }

  void validatePattern(int start) throws NotFoundException {
    // First, sum up the total size of our four categories of stripe sizes;
    int[] sizes = {0, 0, 0, 0};
    int[] counts = {0, 0, 0, 0};
    int end = decodeRowResult.length() - 1;

    // We break out of this loop in the middle, in order to handle
    // inter-character spaces properly.
    int pos = start;
    for (int i = 0; true; i++) {
      int pattern = CHARACTER_ENCODINGS[decodeRowResult.charAt(i)];
      for (int j = 6; j >= 0; j--) {
        // Even j = bars, while odd j = spaces. Categories 2 and 3 are for
        // long stripes, while 0 and 1 are for short stripes.
        int category = (j & 1) + (pattern & 1) * 2;
        sizes[category] += counters[pos + j];
        counts[category]++;
        pattern >>= 1;
      }
      if (i >= end) {
        break;
      }
      // We ignore the inter-character space - it could be of any size.
      pos += 8;
    }

    // Calculate our allowable size thresholds using fixed-point math.
    int[] maxes = new int[4];
    int[] mins = new int[4];
    // Define the threshold of acceptability to be the midpoint between the
    // average small stripe and the average large stripe. No stripe lengths
    // should be on the "wrong" side of that line.
    for (int i = 0; i < 2; i++) {
      mins[i] = 0;  // Accept arbitrarily small "short" stripes.
      mins[i + 2] = ((sizes[i] << INTEGER_MATH_SHIFT) / counts[i] +
                     (sizes[i + 2] << INTEGER_MATH_SHIFT) / counts[i + 2]) >> 1;
      maxes[i] = mins[i + 2];
      maxes[i + 2] = (sizes[i + 2] * MAX_ACCEPTABLE + PADDING) / counts[i + 2];
    }

    // Now verify that all of the stripes are within the thresholds.
    pos = start;
    for (int i = 0; true; i++) {
      int pattern = CHARACTER_ENCODINGS[decodeRowResult.charAt(i)];
      for (int j = 6; j >= 0; j--) {
        // Even j = bars, while odd j = spaces. Categories 2 and 3 are for
        // long stripes, while 0 and 1 are for short stripes.
        int category = (j & 1) + (pattern & 1) * 2;
        int size = counters[pos + j] << INTEGER_MATH_SHIFT;
        if (size < mins[category] || size > maxes[category]) {
          throw NotFoundException.getNotFoundInstance();
        }
        pattern >>= 1;
      }
      if (i >= end) {
        break;
      }
      pos += 8;
    }
  }

  /**
   * Records the size of all runs of white and black pixels, starting with white.
   * This is just like recordPattern, except it records all the counters, and
   * uses our builtin "counters" member for storage.
   * @param row row to count from
   */
  private void setCounters(BitArray row) throws NotFoundException {
    counterLength = 0;
    // Start from the first white bit.
    int i = row.getNextUnset(0);
    int end = row.getSize();
    if (i >= end) {
      throw NotFoundException.getNotFoundInstance();
    }
    boolean isWhite = true;
    int count = 0;
    for (; i < end; i++) {
      if (row.get(i) ^ isWhite) { // that is, exactly one is true
        count++;
      } else {
        counterAppend(count);
        count = 1;
        isWhite = !isWhite;
      }
    }
    counterAppend(count);
  }

  private void counterAppend(int e) {
    counters[counterLength] = e;
    counterLength++;
    if (counterLength >= counters.length) {
      int[] temp = new int[counterLength * 2];
      System.arraycopy(counters, 0, temp, 0, counterLength);
      counters = temp;
    }
  }

  private int findStartPattern() throws NotFoundException {
    for (int i = 1; i < counterLength; i += 2) {
      int charOffset = toNarrowWidePattern(i);
      if (charOffset != -1 && arrayContains(STARTEND_ENCODING, ALPHABET[charOffset])) {
        // Look for whitespace before start pattern, >= 50% of width of start pattern
        // We make an exception if the whitespace is the first element.
        int patternSize = 0;
        for (int j = i; j < i + 7; j++) {
          patternSize += counters[j];
        }
        if (i == 1 || counters[i-1] >= patternSize / 2) {
          return i;
        }
      }
    }
    throw NotFoundException.getNotFoundInstance();
  }

  static boolean arrayContains(char[] array, char key) {
    if (array != null) {
      for (char c : array) {
        if (c == key) {
          return true;
        }
      }
    }
    return false;
  }

  // Assumes that counters[position] is a bar.
  private int toNarrowWidePattern(int position) {
    int end = position + 7;
    if (end >= counterLength) {
      return -1;
    }
    // First element is for bars, second is for spaces.
    int[] maxes = {0, 0};
    int[] mins = {Integer.MAX_VALUE, Integer.MAX_VALUE};
    int[] thresholds = {0, 0};

    for (int i = 0; i < 2; i++) {
      for (int j = position + i; j < end; j += 2) {
        if (counters[j] < mins[i]) {
          mins[i] = counters[j];
        }
        if (counters[j] > maxes[i]) {
          maxes[i] = counters[j];
        }
      }
      thresholds[i] = (mins[i] + maxes[i]) / 2;
    }

    int bitmask = 1 << 7;
    int pattern = 0;
    for (int i = 0; i < 7; i++) {
      int barOrSpace = i & 1;
      bitmask >>= 1;
      if (counters[position + i] > thresholds[barOrSpace]) {
        pattern |= bitmask;
      }
    }

    for (int i = 0; i < CHARACTER_ENCODINGS.length; i++) {
      if (CHARACTER_ENCODINGS[i] == pattern) {
        return i;
      }
    }
    return -1;
  }

}