網上找的方法試了一下，還不錯效果：
先將圖片隱藏hidden，然後當圖片載入完成bindload後再將圖片漸漸顯示出來，高度設為auto，這樣效果還不錯
1.wxml

<image hidden="{{!showPic}}" animation="{{animationData}}" style="opacity:0;height:auto" bindload="showPicture" src='{{info.img}}' mode="widthFix"></image>

2.js

showPicture: function (){
    let that = this
 

    let show = that.data.showPic
    let animation = wx.createAnimation({
      duration: 500,
      timingFunction: 'ease-in',
      delay: 0
    })
    show = true
    animation.opacity(1).step()
    that.setData({
      showPic: show,
      animationData: animation.export()
    })
  },