使用Zxing.net进行一维条码识别，如果自动识别解码对Code39条码解码的情况下可能会出现解码错误的情况（这里的错误是指解码后的数据和原来进行编码的数据不一致，进行编码的数据均为Code39的合法字符）。原因：自动解码会尝试目前所有支持类型的解码，包括Code39Extended模式。Code39和Code39Extended 是相同的方法处理，在进行Code39解码后会判断是否使用了Code39Extended模式，使用了扩展的话就会再次对返回的结果进行Code39Extended解码。文件所在位置：lib\oned\Code39Reader.cs 代码如下：
/*
* 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.
*/
using System;
using System.Collections.Generic;
using System.Text;
using ZXing.Common;
namespace ZXing.OneD
{
/// <summary>
/// <p>Decodes Code 39 barcodes. This does not support "Full ASCII Code 39" yet.</p>
/// <author>Sean Owen</author>
/// @see Code93Reader
/// </summary>
public sealed class Code39Reader : OneDReader
{
internal static String ALPHABET_STRING = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. *$/+%";
private static readonly char[] ALPHABET = ALPHABET_STRING.ToCharArray();
/// <summary>
/// Returns a string with all possible characters
/// </summary>
public static string Alphabet
{
get
{
return ALPHABET_STRING;
}
}
/// <summary>
/// These represent the encodings of characters, as patterns of wide and narrow bars.
/// The 9 least-significant bits of each int correspond to the pattern of wide and narrow,
/// with 1s representing "wide" and 0s representing narrow.
/// </summary>
internal static int[] CHARACTER_ENCODINGS = {
0x034, 0x121, 0x061, 0x160, 0x031, 0x130, 0x070, 0x025, 0x124, 0x064, // 0-9
0x109, 0x049, 0x148, 0x019, 0x118, 0x058, 0x00D, 0x10C, 0x04C, 0x01C, // A-J
0x103, 0x043, 0x142, 0x013, 0x112, 0x052, 0x007, 0x106, 0x046, 0x016, // K-T
0x181, 0x0C1, 0x1C0, 0x091, 0x190, 0x0D0, 0x085, 0x184, 0x0C4, 0x094, // U-*
0x0A8, 0x0A2, 0x08A, 0x02A // $-%
};
private static readonly int ASTERISK_ENCODING = CHARACTER_ENCODINGS[39];
private readonly bool usingCheckDigit;
private readonly bool extendedMode;
private readonly StringBuilder decodeRowResult;
private readonly int[] counters;
/// <summary>
/// Creates a reader that assumes all encoded data is data, and does not treat the final
/// character as a check digit. It will not decoded "extended Code 39" sequences.
/// </summary>
public Code39Reader()
:this(false)
{
}
/// <summary>
/// Creates a reader that can be configured to check the last character as a check digit.
/// It will not decoded "extended Code 39" sequences.
/// </summary>
/// <param name="usingCheckDigit">if true, treat the last data character as a check digit, not
/// data, and verify that the checksum passes.</param>
public Code39Reader(bool usingCheckDigit)
:this(usingCheckDigit, false)
{
}
/// <summary>
/// Creates a reader that can be configured to check the last character as a check digit,
/// or optionally attempt to decode "extended Code 39" sequences that are used to encode
/// the full ASCII character set.
/// </summary>
/// <param name="usingCheckDigit">if true, treat the last data character as a check digit, not
/// data, and verify that the checksum passes.</param>
/// <param name="extendedMode">if true, will attempt to decode extended Code 39 sequences in the text.</param>
public Code39Reader(bool usingCheckDigit, bool extendedMode)
{
this.usingCheckDigit = usingCheckDigit;
this.extendedMode = extendedMode;
decodeRowResult = new StringBuilder(20);
counters = new int[9];
}
/// <summary>
/// <p>Attempts to decode a one-dimensional barcode format given a single row of
/// an image.</p>
/// </summary>
/// <param name="rowNumber">row number from top of the row</param>
/// <param name="row">the black/white pixel data of the row</param>
/// <param name="hints">decode hints</param>
/// <returns><see cref="Result"/>containing encoded string and start/end of barcode</returns>
override public Result decodeRow(int rowNumber, BitArray row, IDictionary<DecodeHintType, object> hints)
{
for (var index = 0; index < counters.Length; index++)
counters[index] = 0;
decodeRowResult.Length = 0;
int[] start = findAsteriskPattern(row, counters);
if (start == null)
return null;
// Read off white space
int nextStart = row.getNextSet(start[1]);
int end = row.Size;
char decodedchar;
int lastStart;
do
{
if (!recordPattern(row, nextStart, counters))
return null;
int pattern = toNarrowWidePattern(counters);
if (pattern < 0)
{
return null;
}
if (!patternTochar(pattern, out decodedchar))
return null;
decodeRowResult.Append(decodedchar);
lastStart = nextStart;
foreach (int counter in counters)
{
nextStart += counter;
}
// Read off white space
nextStart = row.getNextSet(nextStart);
}
while (decodedchar != '*');
decodeRowResult.Length = decodeRowResult.Length - 1;
// remove asterisk
// Look for whitespace after pattern:
int lastPatternSize = 0;
foreach (int counter in counters)
{
lastPatternSize += counter;
}
int whiteSpaceAfterEnd = nextStart - lastStart - lastPatternSize;
// If 50% of last pattern size, following last pattern, is not whitespace, fail
// (but if it's whitespace to the very end of the image, that's OK)
if (nextStart != end && (whiteSpaceAfterEnd << 1) < lastPatternSize)
{
return null;
}
// overriding constructor value is possible
bool useCode39CheckDigit = usingCheckDigit;
if (hints != null && hints.ContainsKey(DecodeHintType.ASSUME_CODE_39_CHECK_DIGIT))
{
useCode39CheckDigit = (bool) hints[DecodeHintType.ASSUME_CODE_39_CHECK_DIGIT];
}
if (useCode39CheckDigit)
{
int max = decodeRowResult.Length - 1;
int total = 0;
for (int i = 0; i < max; i++)
{
total += ALPHABET_STRING.IndexOf(decodeRowResult[i]);
}
if (decodeRowResult[max] != ALPHABET[total % 43])
{
return null;
}
decodeRowResult.Length = max;
}
if (decodeRowResult.Length == 0)
{
// false positive
return null;
}
// overriding constructor value is possible
bool useCode39ExtendedMode = extendedMode;
if (hints != null && hints.ContainsKey(DecodeHintType.USE_CODE_39_EXTENDED_MODE))
{
useCode39ExtendedMode = (bool)hints[DecodeHintType.USE_CODE_39_EXTENDED_MODE];
}
String resultString;
if (useCode39ExtendedMode)
{
resultString = decodeExtended(decodeRowResult.ToString());
if (resultString == null)
{
if (hints != null &&
hints.ContainsKey(DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE) &&
Convert.Toboolean(hints[DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE]))
resultString = decodeRowResult.ToString(); else
return null;
}
} else
{
resultString = decodeRowResult.ToString();
}
float left = (start[1] + start[0])/2.0f;
float right = lastStart + lastPatternSize / 2.0f;
var resultPointCallback = hints == null || !hints.ContainsKey(DecodeHintType.NEED_RESULT_POINT_CALLBACK)
? null
: (ResultPointCallback) hints[DecodeHintType.NEED_RESULT_POINT_CALLBACK];
if (resultPointCallback != null)
{
resultPointCallback(new ResultPoint(left, rowNumber));
resultPointCallback(new ResultPoint(right, rowNumber));
}
return new Result(
resultString,
null,
new[]
{
new ResultPoint(left, rowNumber),
new ResultPoint(right, rowNumber)
}
,
BarcodeFormat.CODE_39);
}
private static int[] findAsteriskPattern(BitArray row, int[] counters)
{
int width = row.Size;
int rowOffset = row.getNextSet(0);
int counterPosition = 0;
int patternStart = rowOffset;
bool isWhite = false;
int patternLength = counters.Length;
for (int i = rowOffset; i < width; i++)
{
if (row[i] ^ isWhite)
{
counters[counterPosition]++;
} else
{
if (counterPosition == patternLength - 1)
{
if (toNarrowWidePattern(counters) == ASTERISK_ENCODING)
{
// Look for whitespace before start pattern, >= 50% of width of start pattern
if (row.isRange(Math.Max(0, patternStart - ((i - patternStart) >> 1)), patternStart, false))
{
return new int[] { patternStart, i };
}
}
patternStart += counters[0] + counters[1];
Array.Copy(counters, 2, counters, 0, patternLength - 2);
counters[patternLength - 2] = 0;
counters[patternLength - 1] = 0;
counterPosition--;
} else
{
counterPosition++;
}
counters[counterPosition] = 1;
isWhite = !isWhite;
}
}
return null;
}
// For efficiency, returns -1 on failure. Not throwing here saved as many as 700 exceptions
// per image when using some of our blackbox images.
private static int toNarrowWidePattern(int[] counters)
{
int numCounters = counters.Length;
int maxNarrowCounter = 0;
int wideCounters;
do
{
int minCounter = Int32.MaxValue;
foreach (var counter in counters)
{
if (counter < minCounter && counter > maxNarrowCounter)
{
minCounter = counter;
}
}
maxNarrowCounter = minCounter;
wideCounters = 0;
int totalWideCountersWidth = 0;
int pattern = 0;
for (int i = 0; i < numCounters; i++)
{
int counter = counters[i];
if (counter > maxNarrowCounter)
{
pattern |= 1 << (numCounters - 1 - i);
wideCounters++;
totalWideCountersWidth += counter;
}
}
if (wideCounters == 3)
{
// Found 3 wide counters, but are they close enough in width?
// We can perform a cheap, conservative check to see if any individual
// counter is more than 1.5 times the average:
for (int i = 0; i < numCounters && wideCounters > 0; i++)
{
int counter = counters[i];
if (counter > maxNarrowCounter)
{
wideCounters--;
// totalWideCountersWidth = 3 * average, so this checks if counter >= 3/2 * average
if ((counter << 1) >= totalWideCountersWidth)
{
return -1;
}
}
}
return pattern;
}
}
while (wideCounters > 3);
return -1;
}
private static bool patternTochar(int pattern, out char c)
{
for (int i = 0; i < CHARACTER_ENCODINGS.Length; i++)
{
if (CHARACTER_ENCODINGS[i] == pattern)
{
c = ALPHABET[i];
return true;
}
}
c = '*';
return false;
}
private static String decodeExtended(String encoded)
{
int length = encoded.Length;
StringBuilder decoded = new StringBuilder(length);
for (int i = 0; i < length; i++)
{
char c = encoded[i];
if (c == '+' || c == '$' || c == '%' || c == '/')
{
if (i + 1 >= encoded.Length)
{
return null;
}
char next = encoded[i + 1];
char decodedchar = '\0';
switch (c)
{
case '+':
// +A to +Z map to a to z
if (next >= 'A' && next <= 'Z')
{
decodedchar = (char)(next + 32);
} else
{
return null;
}
break;
case '$':
// $A to $Z map to control codes SH to SB
if (next >= 'A' && next <= 'Z')
{
decodedchar = (char)(next - 64);
} else
{
return null;
}
break;
case '%':
// %A to %E map to control codes ESC to US
if (next >= 'A' && next <= 'E')
{
decodedchar = (char)(next - 38);
} else if (next >= 'F' && next <= 'W')
{
decodedchar = (char)(next - 11);
} else
{
return null;
}
break;
case '/':
// /A to /O map to ! to , and /Z maps to :
if (next >= 'A' && next <= 'O')
{
decodedchar = (char)(next - 32);
} else if (next == 'Z')
{
decodedchar = ':';
} else
{
return null;
}
break;
}
decoded.Append(decodedchar);
// bump up i again since we read two characters
i++;
} else
{
decoded.Append(c);
}
}
return decoded.ToString();
}
}
}以上是Zxing.net的一个Code39解码的类，出现问题的方法为decodeRow。
/// <summary>
/// <p>Attempts to decode a one-dimensional barcode format given a single row of
/// an image.</p>
/// </summary>
/// <param name="rowNumber">row number from top of the row</param>
/// <param name="row">the black/white pixel data of the row</param>
/// <param name="hints">decode hints</param>
/// <returns><see cref="Result"/>containing encoded string and start/end of barcode</returns>
override public Result decodeRow(int rowNumber, BitArray row, IDictionary<DecodeHintType, object> hints)
{
for (var index = 0; index < counters.Length; index++)
counters[index] = 0;
decodeRowResult.Length = 0;
int[] start = findAsteriskPattern(row, counters);
if (start == null)
return null;
// Read off white space
int nextStart = row.getNextSet(start[1]);
int end = row.Size;
char decodedchar;
int lastStart;
do
{
if (!recordPattern(row, nextStart, counters))
return null;
int pattern = toNarrowWidePattern(counters);
if (pattern < 0)
{
return null;
}
if (!patternTochar(pattern, out decodedchar))
return null;
decodeRowResult.Append(decodedchar);
lastStart = nextStart;
foreach (int counter in counters)
{
nextStart += counter;
}
// Read off white space
nextStart = row.getNextSet(nextStart);
}
while (decodedchar != '*');
decodeRowResult.Length = decodeRowResult.Length - 1;
// remove asterisk
// Look for whitespace after pattern:
int lastPatternSize = 0;
foreach (int counter in counters)
{
lastPatternSize += counter;
}
int whiteSpaceAfterEnd = nextStart - lastStart - lastPatternSize;
// If 50% of last pattern size, following last pattern, is not whitespace, fail
// (but if it's whitespace to the very end of the image, that's OK)
if (nextStart != end && (whiteSpaceAfterEnd << 1) < lastPatternSize)
{
return null;
}
// overriding constructor value is possible
bool useCode39CheckDigit = usingCheckDigit;
if (hints != null && hints.ContainsKey(DecodeHintType.ASSUME_CODE_39_CHECK_DIGIT))
{
useCode39CheckDigit = (bool) hints[DecodeHintType.ASSUME_CODE_39_CHECK_DIGIT];
}
if (useCode39CheckDigit)
{
int max = decodeRowResult.Length - 1;
int total = 0;
for (int i = 0; i < max; i++)
{
total += ALPHABET_STRING.IndexOf(decodeRowResult[i]);
}
if (decodeRowResult[max] != ALPHABET[total % 43])
{
return null;
}
decodeRowResult.Length = max;
}
if (decodeRowResult.Length == 0)
{
// false positive
return null;
}
// overriding constructor value is possible
bool useCode39ExtendedMode = extendedMode;
if (hints != null && hints.ContainsKey(DecodeHintType.USE_CODE_39_EXTENDED_MODE))
{
useCode39ExtendedMode = (bool)hints[DecodeHintType.USE_CODE_39_EXTENDED_MODE];
}
String resultString;
if (useCode39ExtendedMode)
{
resultString = decodeExtended(decodeRowResult.ToString());
if (resultString == null)
{
if (hints != null &&
hints.ContainsKey(DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE) &&
Convert.Toboolean(hints[DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE]))
resultString = decodeRowResult.ToString(); else
return null;
}
} else
{
resultString = decodeRowResult.ToString();
}
float left = (start[1] + start[0])/2.0f;
float right = lastStart + lastPatternSize / 2.0f;
var resultPointCallback = hints == null || !hints.ContainsKey(DecodeHintType.NEED_RESULT_POINT_CALLBACK)
? null
: (ResultPointCallback) hints[DecodeHintType.NEED_RESULT_POINT_CALLBACK];
if (resultPointCallback != null)
{
resultPointCallback(new ResultPoint(left, rowNumber));
resultPointCallback(new ResultPoint(right, rowNumber));
}
return new Result(
resultString,
null,
new[]
{
new ResultPoint(left, rowNumber),
new ResultPoint(right, rowNumber)
}
,
BarcodeFormat.CODE_39);
}在这个方法中有以下代码片段：
if (useCode39ExtendedMode)
{
resultString = decodeExtended(decodeRowResult.ToString());
if (resultString == null)
{
if (hints != null &&
hints.ContainsKey(DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE) &&
Convert.Toboolean(hints[DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE]))
resultString = decodeRowResult.ToString(); else
return null;
}
} else
{
resultString = decodeRowResult.ToString();
}这个方法中通useCode39ExtendedMode来判断是否使用了扩展模式，如果使用则再次解码。这样就会导致二次解码，所以得到的解码数据是错误的。我的解决方法是一个极其笨拙方式，新增一个方法对已经返回的结果进行判断，判断其所有字符是否在Code39允许的范围内。如果得到的数据已经正确，则无需再次进行Code39Extended的解码。
private bool isCharacterinCode39(string decodestring)
{
bool result = true;
if (!string.IsNullOrEmpty(decodestring))
{
for (int i = 0; i < decodestring.Length; i++)
{
if (!ALPHABET_STRING.Contains(decodestring[i].ToString()))
{
result = false;
break;
}
}
}
return result;
}然后将decodeRow方法中的if (useCode39ExtendedMode)替换为if(useCode39ExtendedMode&& !isCharacterinCode39(decodeRowResult.ToString())) 。这样的话基本上算是解决了这个BUG。
override public Result decodeRow(int rowNumber, BitArray row, IDictionary<DecodeHintType, object> hints)
{
for (var index = 0; index < counters.Length; index++)
counters[index] = 0;
decodeRowResult.Length = 0;
int[] start = findAsteriskPattern(row, counters);
if (start == null)
return null;
// Read off white space
int nextStart = row.getNextSet(start[1]);
int end = row.Size;
char decodedchar;
int lastStart;
do
{
if (!recordPattern(row, nextStart, counters))
return null;
int pattern = toNarrowWidePattern(counters);
if (pattern < 0)
{
return null;
}
if (!patternTochar(pattern, out decodedchar))
return null;
decodeRowResult.Append(decodedchar);
lastStart = nextStart;
foreach (int counter in counters)
{
nextStart += counter;
}
// Read off white space
nextStart = row.getNextSet(nextStart);
}
while (decodedchar != '*');
decodeRowResult.Length = decodeRowResult.Length - 1;
// remove asterisk
// Look for whitespace after pattern:
int lastPatternSize = 0;
foreach (int counter in counters)
{
lastPatternSize += counter;
}
int whiteSpaceAfterEnd = nextStart - lastStart - lastPatternSize;
// If 50% of last pattern size, following last pattern, is not whitespace, fail
// (but if it's whitespace to the very end of the image, that's OK)
if (nextStart != end && (whiteSpaceAfterEnd << 1) < lastPatternSize)
{
return null;
}
// overriding constructor value is possible
bool useCode39CheckDigit = usingCheckDigit;
if (hints != null && hints.ContainsKey(DecodeHintType.ASSUME_CODE_39_CHECK_DIGIT))
{
useCode39CheckDigit = (bool) hints[DecodeHintType.ASSUME_CODE_39_CHECK_DIGIT];
}
if (useCode39CheckDigit)
{
int max = decodeRowResult.Length - 1;
int total = 0;
for (int i = 0; i < max; i++)
{
total += ALPHABET_STRING.IndexOf(decodeRowResult[i]);
}
if (decodeRowResult[max] != ALPHABET[total % 43])
{
return null;
}
decodeRowResult.Length = max;
}
if (decodeRowResult.Length == 0)
{
// false positive
return null;
}
// overriding constructor value is possible
bool useCode39ExtendedMode = extendedMode;
if (hints != null && hints.ContainsKey(DecodeHintType.USE_CODE_39_EXTENDED_MODE))
{
useCode39ExtendedMode = (bool)hints[DecodeHintType.USE_CODE_39_EXTENDED_MODE];
}
String resultString;
if (useCode39ExtendedMode && !isCharacterinCode39(decodeRowResult.ToString()))
{
resultString = decodeExtended(decodeRowResult.ToString());
if (resultString == null)
{
if (hints != null &&
hints.ContainsKey(DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE) &&
Convert.Toboolean(hints[DecodeHintType.RELAXED_CODE_39_EXTENDED_MODE]))
resultString = decodeRowResult.ToString(); else
return null;
}
} else
{
resultString = decodeRowResult.ToString();
}
float left = (start[1] + start[0])/2.0f;
float right = lastStart + lastPatternSize / 2.0f;
var resultPointCallback = hints == null || !hints.ContainsKey(DecodeHintType.NEED_RESULT_POINT_CALLBACK)
? null
: (ResultPointCallback) hints[DecodeHintType.NEED_RESULT_POINT_CALLBACK];
if (resultPointCallback != null)
{
resultPointCallback(new ResultPoint(left, rowNumber));
resultPointCallback(new ResultPoint(right, rowNumber));
}
return new Result(
resultString,
null,
new[]
{
new ResultPoint(left, rowNumber),
new ResultPoint(right, rowNumber)
}
,
BarcodeFormat.CODE_39);
}备注：为了验证Zxing.net解码错误的问题，对已经生成的条码在草料进行了解码测试。经过草料解码得到的数据是和编码前的数据一致。为了再一次确认问题，又通过MessagingToolkit.Barcode(.net)进行了相关测试进一步确认了问题。条码的读写之所以没有使用MessagingToolkit.Barcode，是因为一开始使用的就是Zxing.net。Zxing.net是基于Java的一个条形码读写开源项目zxing而写的，所以这个Java开源项目应该有相同的问题。在Zxing.net开源项目首页也已经提到了（http://zxingnet.codeplex.com/）。
转载请注明：清风亦平凡 » 关于Zxing.net 自动解码Code39的BUG
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