如何从 html 图像中获取 base64 编码数据

2022-01-21 00:00:00 image base64 javascript html

我有一个注册表单，用户可以在其中选择头像.他们有两种可能:

I have a registration form where users can choose an avatar. They have 2 possibilities:

  1. 选择默认头像
  2. 上传自己的头像

在我的 HTML 页面中有这个.

In my HTML page I have this.

<img id="preview" src="img/default_1.png">

它显示选择的头像.我使用 File Api 让用户上传自己的图像.这使得 HTML 图像的 src 变成了这样.

It displays the chosen avatar. I use the File Api to let users upload their own image. That makes the src of the HTML image to something like this.

<img id="preview" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgA... />

当他们发布注册表单时.数据将被发送到 REST 服务.当用户自己上传头像时，我可以发送 base64 编码数据.但是如何处理默认头像?它是一个 url 而不是 base64 编码的数据.

When they post the registration form. The data will be sent to a REST service. I can send the base64 encoded data when a user uploaded an avatar himself. But how do I handle the default avatar? It is an url instead of base64 encoded data.

推荐答案

你可以试试下面的例子http://jsfiddle.net/xKJB8/3/

<img id="preview" src="http://www.gravatar.com/avatar/0e39d18b89822d1d9871e0d1bc839d06?s=128&d=identicon&r=PG">
<canvas id="myCanvas" />

<小时>

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var img = document.getElementById("preview");
ctx.drawImage(img, 10, 10);
alert(c.toDataURL());

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