Android平台二维码之生成，扫描 & 识别

1.二维码的前世今生

“二维条码/二维码（2-dimensional bar code）是用某种特定的几何图形按一定规律在平面（二维方向上）分布的黑白相间的图形记录数据符号信息的；在代码编制上巧妙地利用构成计算机内部逻辑基础的“0”、“1”比特流的概念，使用若干个与二进制相对应的几何形体来表示文字数值信息，通过图象输入设备或光电扫描设备自动识读以实现信息自动处理：它具有条码技术的一些共性：每种码制有其特定的字符集；每个字符占有一定的宽度；具有一定的校验功能等。同时还具有对不同行的信息自动识别功能、及处理图形旋转变化点。 [1] ”

上面是百度百科的解释。既然有二维码，那么肯定有一维码。

一维码。最为常见的就是食品 & 书本后面的条码。

条码起源与20世纪40年代，后来在1970年 UPC码发明，并开始广泛应用与食品包装。

具体的介绍可以看百度百科 一维码。

其实二维码与一维码本质上是类似的，就跟一维数组和二维数组一样。

2.二维码的java支持库

为了让java或者说android方便继承条码的功能，google就开发了一个zxing的库：

https://github.com/zxing/zxing

3.生成二维码

public class EncodeThread {

    public static void encode(final String url, final int width, final int height, final EncodeResult result) {

        if (result == null) {
            return;
        }

        if (TextUtils.isEmpty(url)) {
            result.onEncodeResult(null);
            return;
        }

        new Thread() {
            @Override
            public void run() {
                try {
                    MultiFormatWriter writer = new MultiFormatWriter();
                    Hashtable<EncodeHintType, String> hints = new Hashtable<>();
                    hints.put(EncodeHintType.CHARACTER_SET, "utf-8");
                    BitMatrix bitMatrix = writer.encode(url, BarcodeFormat.QR_CODE, width, height, hints);
                    Bitmap bitmap = parseBitMatrix(bitMatrix);
                    result.onEncodeResult(bitmap);
                    return;
                } catch (WriterException e) {
                    e.printStackTrace();
                }
                result.onEncodeResult(null);
            }
        }.start();

    }

    /**
     * 生成二维码内容<br>
     *
     * @param matrix
     * @return
     */
    public static Bitmap parseBitMatrix(BitMatrix matrix) {
        final int QR_WIDTH = matrix.getWidth();
        final int QR_HEIGHT = matrix.getHeight();
        int[] pixels = new int[QR_WIDTH * QR_HEIGHT];
        //this we using qrcode algorithm
        for (int y = 0; y < QR_HEIGHT; y++) {
            for (int x = 0; x < QR_WIDTH; x++) {
                if (matrix.get(x, y)) {
                    pixels[y * QR_WIDTH + x] = 0xff000000;
                } else {
                    pixels[y * QR_WIDTH + x] = 0xffffffff;
                }
            }
        }
        Bitmap bitmap = Bitmap.createBitmap(QR_WIDTH, QR_HEIGHT, Bitmap.Config.ARGB_8888);
        bitmap.setPixels(pixels, 0, QR_WIDTH, 0, 0, QR_WIDTH, QR_HEIGHT);
        return bitmap;
    }

    public interface EncodeResult {
        void onEncodeResult(Bitmap bitmap);
    }
}

zxing 支持很多条码格式：我们这里使用QR_CODE码。也就是我们常见的微信里面的二维码。

我们先来分析下这段代码：

 MultiFormatWriter writer = new MultiFormatWriter();

这个是一个工具类，把所有支持的几个write写在里面了。

public BitMatrix encode(String contents,
                          BarcodeFormat format,
                          int width, int height,
                          Map<EncodeHintType,?> hints) throws WriterException {

    Writer writer;
    switch (format) {
      case EAN_8:
        writer = new EAN8Writer();
        break;
      case UPC_E:
        writer = new UPCEWriter();
        break;
      case EAN_13:
        writer = new EAN13Writer();
        break;
      case UPC_A:
        writer = new UPCAWriter();
        break;
      case QR_CODE:
        writer = new QRCodeWriter();
        break;
      case CODE_39:
        writer = new Code39Writer();
        break;
      case CODE_93:
        writer = new Code93Writer();
        break;
      case CODE_128:
        writer = new Code128Writer();
        break;
      case ITF:
        writer = new ITFWriter();
        break;
      case PDF_417:
        writer = new PDF417Writer();
        break;
      case CODABAR:
        writer = new CodaBarWriter();
        break;
      case DATA_MATRIX:
        writer = new DataMatrixWriter();
        break;
      case AZTEC:
        writer = new AztecWriter();
        break;
      default:
        throw new IllegalArgumentException("No encoder available for format " + format);
    }
    return writer.encode(contents, format, width, height, hints);
  }

这是官方最新支持的格式，具体看引入的jar里面支持的格式。

对与bitmatrix的结果，通过摸个算法，设置每个点白色，或者黑色。

最后创建一张二维码的图片。

4.识别二维码

如何从一张图片上面，识别二维码呢：

public class ReDecodeThread {

    public static void encode(final Bitmap bitmap, final ReDecodeThreadResult listener) {

        if (listener == null) {
            return;
        }

        if (bitmap == null) {
            listener.onReDecodeResult(null);
            return;
        }

        new Thread() {
            @Override
            public void run() {
                try {
                    MultiFormatReader multiFormatReader = new MultiFormatReader();
                    BitmapLuminanceSource source = new BitmapLuminanceSource(bitmap);
                    BinaryBitmap bitmap1 = new BinaryBitmap(new HybridBinarizer(source));
                    Result result1 = multiFormatReader.decode(bitmap1);
                    listener.onReDecodeResult(result1.getText());
                    return;
                } catch (NotFoundException e) {
                    e.printStackTrace();
                }
                listener.onReDecodeResult(null);
            }
        }.start();

    }

    public interface ReDecodeThreadResult {
        void onReDecodeResult(String url);
    }
}

过程也是很简单，使用MultiFormatReader来分析图片，这里不需要缺人图片的条码格式。

如果分析下源码，就是依次使用每种格式的reader来分析，直到找到合适的为止。

当然回了能够把Bitmap转化成Bitmatrix，然后在分析。

public final class BitmapLuminanceSource extends LuminanceSource{
    private final byte[] luminances;

    public BitmapLuminanceSource(String path) throws FileNotFoundException {
        this(loadBitmap(path));
    }

    public BitmapLuminanceSource(Bitmap bitmap) {
        super(bitmap.getWidth(), bitmap.getHeight());

        int width = bitmap.getWidth();
        int height = bitmap.getHeight();

        int[] pixels = new int[width * height];
        bitmap.getPixels(pixels, 0, width, 0, 0, width, height);

        // In order to measure pure decoding speed, we convert the entire image
        // to a greyscale array
        // up front, which is the same as the Y channel of the
        // YUVLuminanceSource in the real app.
        luminances = new byte[width * height];
        for (int y = 0; y < height; y++) {
            int offset = y * width;
            for (int x = 0; x < width; x++) {
                int pixel = pixels[offset + x];
                int r = (pixel >> 16) & 0xff;
                int g = (pixel >> 8) & 0xff;
                int b = pixel & 0xff;
                if (r == g && g == b) {
                    // Image is already greyscale, so pick any channel.
                    luminances[offset + x] = (byte) r;
                } else {
                    // Calculate luminance cheaply, favoring green.
                    luminances[offset + x] = (byte) ((r + g + g + b) >> 2);
                }
            }
        }
    }

    @Override
    public byte[] getRow(int y, byte[] row) {
        if (y < 0 || y >= getHeight()) {
            throw new IllegalArgumentException("Requested row is outside the image: " + y);
        }
        int width = getWidth();
        if (row == null || row.length < width) {
            row = new byte[width];
        }

        System.arraycopy(luminances, y * width, row, 0, width);
        return row;
    }

    // Since this class does not support cropping, the underlying byte array
    // already contains
    // exactly what the caller is asking for, so give it to them without a copy.
    @Override
    public byte[] getMatrix() {
        return luminances;
    }

    private static Bitmap loadBitmap(String path) throws FileNotFoundException {
        Bitmap bitmap = BitmapFactory.decodeFile(path);
        if (bitmap == null) {
            throw new FileNotFoundException("Couldn't open " + path);
        }
        return bitmap;
    }
}

BitmapLuminanceSource

5.扫描二维码

扫描二维码，其实比上面只多了一步，就是把camera获取的东西直接转换，然后进行识别。

  public void requestPreviewFrame(Handler handler, int message) {
    if (camera != null && previewing) {
      previewCallback.setHandler(handler, message);
      if (useOneShotPreviewCallback) {
        camera.setOneShotPreviewCallback(previewCallback);
      } else {
        camera.setPreviewCallback(previewCallback);
      }
    }
  }

首先把camera预览的数据放入previewCallback中。

final class PreviewCallback implements Camera.PreviewCallback

public void onPreviewFrame(byte[] data, Camera camera) {
    Point cameraResolution = configManager.getCameraResolution();
    if (!useOneShotPreviewCallback) {
      camera.setPreviewCallback(null);
    }
    if (previewHandler != null) {
      Message message = previewHandler.obtainMessage(previewMessage, cameraResolution.x,
          cameraResolution.y, data);
      message.sendToTarget();
      previewHandler = null;
    } else {
      Log.d(TAG, "Got preview callback, but no handler for it");
    }
  }

可以看到，预览的数据data，回传递过来，然后handler的方式传递出去。

接收data的地方：

  @Override
  public void handleMessage(Message message) {
    switch (message.what) {
      case R.id.decode:
        //Log.d(TAG, "Got decode message");
        decode((byte[]) message.obj, message.arg1, message.arg2);
        break;
      case R.id.quit:
        Looper.myLooper().quit();
        break;
    }
  }

然后是decode data

private void decode(byte[] data, int width, int height) {
    long start = System.currentTimeMillis();
    Result rawResult = null;

    //modify here
    byte[] rotatedData = new byte[data.length];
    for (int y = 0; y < height; y++) {
        for (int x = 0; x < width; x++)
            rotatedData[x * height + height - y - 1] = data[x + y * width];
    }
    int tmp = width; // Here we are swapping, that's the difference to #11
    width = height;
    height = tmp;

    PlanarYUVLuminanceSource source = CameraManager.get().buildLuminanceSource(rotatedData, width, height);
    BinaryBitmap bitmap = new BinaryBitmap(new HybridBinarizer(source));
    try {
      rawResult = multiFormatReader.decodeWithState(bitmap);
    } catch (ReaderException re) {
      // continue
    } finally {
      multiFormatReader.reset();
    }

    if (rawResult != null) {
      long end = System.currentTimeMillis();
      Log.d(TAG, "Found barcode (" + (end - start) + " ms):\n" + rawResult.toString());
      Message message = Message.obtain(activity.getHandler(), R.id.decode_succeeded, rawResult);
      Bundle bundle = new Bundle();
      bundle.putParcelable(DecodeThread.BARCODE_BITMAP, source.renderCroppedGreyscaleBitmap());
      message.setData(bundle);
      //Log.d(TAG, "Sending decode succeeded message...");
      message.sendToTarget();
    } else {
      Message message = Message.obtain(activity.getHandler(), R.id.decode_failed);
      message.sendToTarget();
    }
  }

当把camera上的图片转换成BinaryBitmap以后，剩下的事情，就更直接从图片识别是一样的。

PlanarYUVLuminanceSource source = CameraManager.get().buildLuminanceSource(rotatedData, width, height);
    BinaryBitmap bitmap = new BinaryBitmap(new HybridBinarizer(source));

参考：

http://www.cnblogs.com/weixing/archive/2013/08/28/3287120.html