https://itmanual.net/%ec%9c%88%eb%8f%84%ec%9a%b0-%ec%bb%b4%ed%93%a8%ed%84%b0-%eb%a7%88%ec%9a%b0%ec%8a%a4-%ea%b0%90%eb%8f%84-%ec%a1%b0%ec%a0%88-dpi-%ec%84%a4%ec%a0%95-%eb%b0%a9%eb%b2%95/