image转换为base64位
function getBase64(url){
var Img = document.createElement('img');
Img.src=url;
var canvas = document.createElement("canvas"), //创建canvas元素
width=Img.width, //确保canvas的尺寸和图片一样
height=Img.height;
canvas.width=width;
canvas.height=height;
canvas.getContext("2d").drawImage(Img,0,0,width,height); //将图片绘制到canvas中
dataURL=canvas.toDataURL('image/jpeg'); //转换图片为dataURL
}
