https://blog.faceutil.com/2017/04/19/%ec%95%88%ec%b9%b4%eb%a9%94%eb%9d%bc-%ed%8c%8c%ec%9d%bc-%ec%a0%80%ec%9e%a5%ec%9d%80-bitmap%ed%8c%8c%ec%9d%bc%eb%a1%9c-%ec%84%a0%eb%aa%85%ed%95%98%ea%b2%8c-%ec%a0%80%ec%9e%a5-%ed%95%98%ec%84%b8/