/**
     * 得到Bitmap的byte
     * @author netcorner
     * @param bmp
     * @return
     */
    private  byte[] bmpToByteArray(Bitmap bmp) {
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        bmp.compress(Bitmap.CompressFormat.PNG, 100, output);

        byte[] result = output.toByteArray();
        try {
            output.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }

    /**
     * Bitmap转换成byte[]并且进行压缩,压缩到不大于maxkb
     * @param bitmap
     * @param maxkb
     * @return
     */
    public static byte[] bmpToByteArray(Bitmap bitmap, int maxkb) {
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.PNG, 100, output);
        int options = 100;
        while (output.toByteArray().length > maxkb&& options != 10) {
            output.reset(); //清空output
            bitmap.compress(Bitmap.CompressFormat.JPEG, options, output);//这里压缩options%，把压缩后的数据存放到output中
            options -= 10;
        }
        return output.toByteArray();
    }