调整一维条码宽单元窄单元比例（ZXing2.3）

　　最近用到一维条码、二维条码，看了几种方案，选了ZXing，因为即支持一维条码、二维条码的生成，也支持条码的识读。
　　结果在应用的过程中遇到了问题，有的单位使用的是针式打印机，一式多份的，打印出来的一维条码识别率很低。这是个致命的问题，必须要解决。仔细阅读了一维条码的原理、码制，发现一个说法，条码的宽单元与窄单元的比例(W/N Ratio)可以为2至3。看一下打印结果，ZXing打印出来的好像是2，如果调整到3，是不是能提高识别率呢？
　　可是，把ZXing的接口反复看了几遍，没有找到能改的地方，觉得这是一个比较重要的参数，ZXing不提供有点不厚道呀！
　　只好改源码了，阅读了一下源码，发现ZXing确实不支持调整宽窄单元比，因为2是硬编码在代码里的，为了不影响原有的代码，我就自已加一种码制吧，起个名叫Code393，表示宽窄单元比为3的Code39码。把我的代码完整贴一下，改动并不多，加了一点儿注释。还要修改BarcodeFormat、MultiFormatWriter，很简单，这里不做介绍了。

/*
 * Copyright 2010 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.EncodeHintType;
import com.google.zxing.WriterException;
import com.google.zxing.common.BitMatrix;

import java.util.Map;

/**
 * This object renders a CODE39 code as a {@link BitMatrix}.
 * 宽单元这宽度为窄单元的2到3倍，这是我自定义的3倍的单元比
 * 
 * @author [e-mail] (Erik Barbara), Modified by [e-mail]
 */
public final class Code393Writer extends OneDimensionalCodeWriter {

  @Override
  public BitMatrix encode(String contents,
                          BarcodeFormat format,
                          int width,
                          int height,
                          Map<EncodeHintType,?> hints) throws WriterException {
    if (format != BarcodeFormat.CODE_39_3) {
      throw new IllegalArgumentException("Can only encode CODE_39, but got " + format);
    }
    return super.encode(contents, format, width, height, hints);
  }

  @Override
  public boolean[] encode(String contents) {
    int length = contents.length();
    if (length > 80) {
      throw new IllegalArgumentException(
          "Requested contents should be less than 80 digits long, but got " + length);
    }

    int[] widths = new int[9];
    //int codeWidth = 24 + 1 + length;
    int codeWidth = 1 + length;//每个字符间的空
    for (int i = 0; i < length; i++) {
      int indexInString = Code39Reader.ALPHABET_STRING.indexOf(contents.charAt(i));
      if (indexInString < 0) {
        throw new IllegalArgumentException("Bad contents: " + contents);
      }
      toIntArray(Code39Reader.CHARACTER_ENCODINGS[indexInString], widths);
      for (int width : widths) {
        codeWidth += width;
      }
    }
    toIntArray(Code39Reader.CHARACTER_ENCODINGS[39], widths);
    //起始码、结束码占的宽度
    for (int width : widths) {
    	codeWidth += width;
    }
    for (int width : widths) {
    	codeWidth += width;
    }
    boolean[] result = new boolean[codeWidth];
    int pos = appendPattern(result, 0, widths, true);
    int[] narrowWhite = {1};
    pos += appendPattern(result, pos, narrowWhite, false);
    //append next character to bytematrix
    for(int i = length-1; i >= 0; i--) {
      int indexInString = Code39Reader.ALPHABET_STRING.indexOf(contents.charAt(i));
      toIntArray(Code39Reader.CHARACTER_ENCODINGS[indexInString], widths);
      pos += appendPattern(result, pos, widths, true);
      pos += appendPattern(result, pos, narrowWhite, false);
    }
    toIntArray(Code39Reader.CHARACTER_ENCODINGS[39], widths);
    pos += appendPattern(result, pos, widths, true);
    return result;
  }

  private static void toIntArray(int a, int[] toReturn) {
    for (int i = 0; i < 9; i++) {
      int temp = a & (1 << i);
      toReturn[i] = temp == 0 ? 1 : 3;//原来此处为3
    }
  }

}

　　调整好了，打印一试，识别率比较令人满意。
　　另，此项修改，不知对条码识别有没有影响，本人没有检查识读部分的代码。
　　本人原创，转载请保留原文地址：http://wallimn.iteye.com/blog/2111896