1.srcset
<img src="./../img/ad001-l.png" alt=""
srcset="./../img/ad001.png 300w, ./../img/ad001-m.png 800w, ./../img/ad001-l.png 1600w">
2.picture
<picture>
<source srcset="img/a.png" />
<source srcset="img/a.png" />
<img src="img/2.png>
</picture>
3.SVG
在線值作矢量圖: