CSS控制图片img组件4:3等比缩放

<div class="pic">
    <img src=""/>
</div>

img {
        width: 100%;
        position:absolute;
        height:100%;
        left: 0;
        top:0;
}
.pic {
        position:relative;
        width: 100%;
        height: 0;
        padding-bottom: 75%;
        background-color: #FFF;
}