zxing/csharp/oned/ITFReader.cs

/*
* 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.oned
{
    /**
     * <p>Implements decoding of the EAN-13 format.</p>
     *
     * @author dswitkin@google.com (Daniel Switkin)
     * @author Sean Owen
     * @author alasdair@google.com (Alasdair Mackintosh)
     */

    using System.Text;
    using com.google.zxing.common;

    public sealed class ITFReader : AbstractOneDReader
    { 
          private static  int MAX_AVG_VARIANCE = (int) (PATTERN_MATCH_RESULT_SCALE_FACTOR * 0.42f);
          private static  int MAX_INDIVIDUAL_VARIANCE = (int) (PATTERN_MATCH_RESULT_SCALE_FACTOR * 0.8f);

          private static  int W = 3; // Pixel width of a wide line
          private static  int N = 1; // Pixed width of a narrow line

          // Stores the actual narrow line width of the image being decoded.
          private int narrowLineWidth = -1;

          /**
           * Start/end guard pattern.
           *
           * Note: The end pattern is reversed because the row is reversed before
           * searching for the END_PATTERN
           */
          private static  int[] START_PATTERN = {N, N, N, N};
          private static  int[] END_PATTERN_REVERSED = {N, N, W};

          /**
           * Patterns of Wide / Narrow lines to indicate each digit
           */
          private static  int[][] PATTERNS = new int[][]{
              new int[]{N, N, W, W, N}, // 0
              new int[]{W, N, N, N, W}, // 1
              new int[]{N, W, N, N, W}, // 2
              new int[]{W, W, N, N, N}, // 3
              new int[]{N, N, W, N, W}, // 4
              new int[]{W, N, W, N, N}, // 5
              new int[]{N, W, W, N, N}, // 6
              new int[]{N, N, N, W, W}, // 7
              new int[]{W, N, N, W, N}, // 8
              new int[]{N, W, N, W, N}  // 9
          };

          public override Result decodeRow(int rowNumber, BitArray row, System.Collections.Hashtable hints) {

            StringBuilder result = new StringBuilder(20);

            // Find out where the Middle section (payload) starts & ends
            int[] startRange = decodeStart(row);
            int[] endRange = decodeEnd(row);

            decodeMiddle(row, startRange[1], endRange[0], result);

            string resultString = result.ToString();

            // To avoid false positives with 2D barcodes (and other patterns), make
            // an assumption that the decoded string must be 6, 10 or 14 digits.
            int length = resultString.Length;
            if (length != 6 && length != 10 && length != 14) {
              throw new ReaderException();
            }

            return new Result(
                resultString,
                null, // no natural byte representation for these barcodes
                new ResultPoint[] { new GenericResultPoint(startRange[1], (float) rowNumber),
                                    new GenericResultPoint(startRange[0], (float) rowNumber)},
                BarcodeFormat.ITF);
          }

          /**
           * @param row          row of black/white values to search
           * @param payloadStart offset of start pattern
           * @param resultString {@link StringBuilder} to Append decoded chars to
           * @throws ReaderException if decoding could not complete successfully
           */
          static void decodeMiddle(BitArray row, int payloadStart, int payloadEnd, StringBuilder resultString) {

            // Digits are interleaved in pairs - 5 black lines for one digit, and the
            // 5
            // interleaved white lines for the second digit.
            // Therefore, need to scan 10 lines and then
            // split these into two arrays
            int[] counterDigitPair = new int[10];
            int[] counterBlack = new int[5];
            int[] counterWhite = new int[5];

            while (payloadStart < payloadEnd) {

              // Get 10 runs of black/white.
              recordPattern(row, payloadStart, counterDigitPair);
              // Split them into each array
              for (int k = 0; k < 5; k++) {
                int twoK = k << 1;
                counterBlack[k] = counterDigitPair[twoK];
                counterWhite[k] = counterDigitPair[twoK + 1];
              }

              int bestMatch = decodeDigit(counterBlack);
              resultString.Append((char) ('0' + bestMatch));
              bestMatch = decodeDigit(counterWhite);
              resultString.Append((char) ('0' + bestMatch));

              for (int i = 0; i < counterDigitPair.Length; i++) {
                payloadStart += counterDigitPair[i];
              }
            }
          }

          /**
           * Identify where the start of the middle / payload section starts.
           *
           * @param row row of black/white values to search
           * @return Array, containing index of start of 'start block' and end of
           *         'start block'
           * @throws ReaderException
           */
          int[] decodeStart(BitArray row) {
            int endStart = skipWhiteSpace(row);
            int[] startPattern = findGuardPattern(row, endStart, START_PATTERN);

            // Determine the width of a narrow line in pixels. We can do this by
            // getting the width of the start pattern and dividing by 4 because its
            // made up of 4 narrow lines.
            this.narrowLineWidth = (startPattern[1] - startPattern[0]) >> 2;

            validateQuietZone(row, startPattern[0]);

            return startPattern;
          }

          /**
           * The start & end patterns must be pre/post fixed by a quiet zone. This
           * zone must be at least 10 times the width of a narrow line.  Scan back until
           * we either get to the start of the barcode or match the necessary number of
           * quiet zone pixels.
           *
           * Note: Its assumed the row is reversed when using this method to find
           * quiet zone after the end pattern.
           *
           * ref: http://www.barcode-1.net/i25code.html
           *
           * @param row bit array representing the scanned barcode.
           * @param startPattern index into row of the start or end pattern.
           * @throws ReaderException if the quiet zone cannot be found, a ReaderException is thrown.
           */
          private void validateQuietZone(BitArray row, int startPattern) {

            int quietCount = this.narrowLineWidth * 10;  // expect to find this many pixels of quiet zone

            for (int i = startPattern - 1; quietCount > 0 && i >= 0; i--) {
              if (row.get(i)) {
                break;
              }
              quietCount--;
            }
            if (quietCount != 0) {
              // Unable to find the necessary number of quiet zone pixels.
              throw new ReaderException();
            }
          }

          /**
           * Skip all whitespace until we get to the first black line.
           *
           * @param row row of black/white values to search
           * @return index of the first black line.
           * @throws ReaderException Throws exception if no black lines are found in the row
           */
          private int skipWhiteSpace(BitArray row) {
            int width = row.getSize();
            int endStart = 0;
            while (endStart < width) {
              if (row.get(endStart)) {
                break;
              }
              endStart++;
            }
            if (endStart == width) {
              throw new ReaderException();
            }

            return endStart;
          }

          /**
           * Identify where the end of the middle / payload section ends.
           *
           * @param row row of black/white values to search
           * @return Array, containing index of start of 'end block' and end of 'end
           *         block'
           * @throws ReaderException
           */

          int[] decodeEnd(BitArray row) {

            // For convenience, reverse the row and then
            // search from 'the start' for the end block
            row.reverse();

            int endStart = skipWhiteSpace(row);
            int[] endPattern;
            try {
              endPattern = findGuardPattern(row, endStart, END_PATTERN_REVERSED);
            } catch (ReaderException e) {
              // Put our row of data back the right way before throwing
              row.reverse();
              throw e;
            }

            // The start & end patterns must be pre/post fixed by a quiet zone. This
            // zone must be at least 10 times the width of a narrow line.
            // ref: http://www.barcode-1.net/i25code.html
            validateQuietZone(row, endPattern[0]);

            // Now recalc the indicies of where the 'endblock' starts & stops to
            // accomodate
            // the reversed nature of the search
            int temp = endPattern[0];
            endPattern[0] = row.getSize() - endPattern[1];
            endPattern[1] = row.getSize() - temp;

            // Put the row back the righ way.
            row.reverse();
            return endPattern;
          }

          /**
           * @param row       row of black/white values to search
           * @param rowOffset position to start search
           * @param pattern   pattern of counts of number of black and white pixels that are
           *                  being searched for as a pattern
           * @return start/end horizontal offset of guard pattern, as an array of two
           *         ints
           * @throws ReaderException if pattern is not found
           */
          int[] findGuardPattern(BitArray row, int rowOffset, int[] pattern) {

            // TODO: This is very similar to implementation in AbstractUPCEANReader. Consider if they can be merged to
            // a single method.

            int patternLength = pattern.Length;
            int[] counters = new int[patternLength];
            int width = row.getSize();
            bool isWhite = false;

            int counterPosition = 0;
            int patternStart = rowOffset;
            for (int x = rowOffset; x < width; x++) {
              bool pixel = row.get(x);
              if ((!pixel && isWhite) || (pixel && !isWhite)) {
                counters[counterPosition]++;
              } else {
                if (counterPosition == patternLength - 1) {
                  if (patternMatchVariance(counters, pattern, MAX_INDIVIDUAL_VARIANCE) < MAX_AVG_VARIANCE) {
                    return new int[]{patternStart, x};
                  }
                  patternStart += counters[0] + counters[1];
                  for (int y = 2; y < patternLength; y++) {
                    counters[y - 2] = counters[y];
                  }
                  counters[patternLength - 2] = 0;
                  counters[patternLength - 1] = 0;
                  counterPosition--;
                } else {
                  counterPosition++;
                }
                counters[counterPosition] = 1;
                isWhite = !isWhite;
              }
            }
            throw new ReaderException();
          }

          /**
           * Attempts to decode a sequence of ITF black/white lines into single
           * digit.
           *
           * @param counters the counts of runs of observed black/white/black/... values
           * @return The decoded digit
           * @throws ReaderException if digit cannot be decoded
           */
          private static int decodeDigit(int[] counters) {

            int bestVariance = MAX_AVG_VARIANCE; // worst variance we'll accept
            int bestMatch = -1;
            int max = PATTERNS.Length;
            for (int i = 0; i < max; i++) {
              int[] pattern = PATTERNS[i];
              int variance = patternMatchVariance(counters, pattern, MAX_INDIVIDUAL_VARIANCE);
              if (variance < bestVariance) {
                bestVariance = variance;
                bestMatch = i;
              }
            }
            if (bestMatch >= 0) {
              return bestMatch;
		        } else {
			        throw new ReaderException();
		        }
	        }
    
    }
}