只有操作拒绝弹窗后 才可以去开启。

wx.saveImageToPhotosAlbum({
    filePath: 'xxx',
    success: (res) => {
     console.log(res)
    },
    fail: (res) => {
      wx.getSetting({
        success: res => {
          let authSetting = res.authSetting
          if (!authSetting['scope.writePhotosAlbum']) {
            wx.openSetting()
          }
        }
      })
    }
  })
}

访问相册不需要权限吧好像 像chooseimage 和choosemedia api都可以直接访问