private Camera.Size calBestPreviewSize(Camera.Parameters camPara,
                                           final int width, final int height) {
        List<Camera.Size> allSupportedSize = camPara.getSupportedPreviewSizes();
        ArrayList<Camera.Size> widthLargerSize = new ArrayList<Camera.Size>();
        for (Camera.Size tmpSize : allSupportedSize) {
            if (tmpSize.width > tmpSize.height) {
                widthLargerSize.add(tmpSize);
            }
        }

        Collections.sort(widthLargerSize, new Comparator<Camera.Size>() {
            @Override
            public int compare(Camera.Size lhs, Camera.Size rhs) {
                int off_one = Math.abs(lhs.width * lhs.height - width * height);
                int off_two = Math.abs(rhs.width * rhs.height - width * height);
                return off_one - off_two;
            }
        });

        return widthLargerSize.get(0);
    }