zxing scan from large photo

在使用zxing开源库的时候，发现比较大的图片无法扫描成功，报如下异常：

com.google.zxing.NotFoundException

通过scale down Bitmap可以解决上述问题，720是一个Magic number，可以根据自己的项目调整

// Scale down the bitmap if it is bigger than we need.
int width = bm.getWidth();
int height = bm.getHeight();
final int targetWidth = 720, targetHeight = 720;
if (width > targetWidth || height > targetHeight) {
    float scale = 0.0f;
    if (width >= height) {
        scale = (float) targetWidth / width;
    } else {
        scale = (float) targetHeight / height;
    }
    int w = Math.round(scale * width);
    int h = Math.round(scale * height);
    bm = Bitmap.createScaledBitmap(bm, w, h, true);
}

比较完整代码如下：

...
new QRCodeScanTask(picturePath).execute();
...

private class QRCodeScanTask extends AsyncTask<Void, Void, Result> {
        private String imagePath;
        private ProgressDialog mProgressDialog;
        public QRCodeScanTask(String imagePath) {
            this.imagePath = imagePath;
        }

        @Override
        public void onPreExecute() {
            mProgressDialog = new ProgressDialog(mActivity);
            mProgressDialog.setMessage(mActivity.getString(R.string.qrcode_scanning));
            mProgressDialog.show();
        }

        public Result doInBackground(Void... params) {
            try{
                MultiFormatReader multiFormatReader = new MultiFormatReader();
                Bitmap bm = BitmapFactory.decodeFile(imagePath);
                // Scale down the bitmap if it is bigger than we need.
                int width = bm.getWidth();
                int height = bm.getHeight();
                final int targetWidth = 720, targetHeight = 720;
                if (width > targetWidth || height > targetHeight) {
                    float scale = 0.0f;
                    if (width >= height) {
                        scale = (float) targetWidth / width;
                    } else {
                        scale = (float) targetHeight / height;
                    }
                    int w = Math.round(scale * width);
                    int h = Math.round(scale * height);
                    bm = Bitmap.createScaledBitmap(bm, w, h, true);
                }

                Result result = multiFormatReader.decodeWithState(new BinaryBitmap(
                    new HybridBinarizer(new BitmapLuminanceSource(bm))));
                return result;
            } catch(Exception e) {
                return null;
            }
        }

        @Override
        public void onPostExecute(Result result){
            mProgressDialog.dismiss();
            if(result == null)
                Toast.makeText(mActivity, R.string.qrcode_notfound, Toast.LENGTH_SHORT).show();
            else
                handleQRCodeResult(result);
        }
    }

PS：

1. 这里有相关的讨论 https://code.google.com/p/zxing/issues/detail?id=513

2. zxing github link: https://github.com/zxing/zxing/

来源：oschina

链接：https://my.oschina.net/u/172402/blog/386590