求大神解决 Illegal string offset 'image' 怎么解决

我这样写
public function index()
{
$slide=Db::table('os_slide')->select();
$slide=json_encode($slide);
print_r($slide);die;
return $this->fetch('index', ['slide' => $slide]);
}
之后输出数组
[
{
id: 1,
cid: 1,
name: "第一张",
description: "",
link: "",
target: "_self",
image: "/uploads/20190708/28bca99b8b9f527f4849f3a9bf00e065.jpg",
phone_image: "/uploads/20190708/28bca99b8b9f527f4849f3a9bf00e065.jpg",
status: 1,
sort: 0
},
{
id: 2,
cid: 1,
name: "第二张",
description: "",
link: "",
target: "_self",
image: "/uploads/20190708/f99647c00d2f1ae370ea1f751cd7b7b2.jpg",
phone_image: "/uploads/20190708/f99647c00d2f1ae370ea1f751cd7b7b2.jpg",
status: 1,
sort: 0
},
{
id: 3,
cid: 1,
name: "第三张",
description: "",
link: "",
target: "_self",
image: "/uploads/20190708/5e489a13431eecdfee3f611dadd2afba.jpg",
phone_image: "/uploads/20190708/5e489a13431eecdfee3f611dadd2afba.jpg",
status: 1,
sort: 0
}
]
但是若是这样单个打印
public function index()
{
$slide=Db::table('os_slide')->select();
$slide=json_encode($slide);
print_r($slide['image']);die;
return $this->fetch('index', ['slide' => $slide]);
}
就会报错
Illegal string offset 'image'
这是怎么一回事啊？