图片上传 base64数据压缩、降低清晰度方法封装

•  函数简单封装：

 function getBase64Image(img) {

            var canvas = document.createElement("canvas");

            var width = img.width;

            var height = img.height;

            // calculate the width and height, constraining the proportions

            if (width > height) {

                if (width > 100) {

                    height = Math.round(height *= 100 / width);

                    width = 100;

                }

            } else {

                if (height > 100) {

                    width = Math.round(width *= 100 / height);

                    height = 100;

                }

            }

            canvas.width = width;  /*设置新的图片的宽度*/

            canvas.height = height; /*设置新的图片的长度*/

            var ctx = canvas.getContext("2d");//开启canvas绘图

            ctx.drawImage(img, 0, 0, width, height); /*绘图*/

            var dataURL = canvas.toDataURL("image/png", 0.8);//降低图片的清晰度

            return dataURL.replace("data:image/png;base64,", "");//返回除去data:image/png;base64,的base64数据

        }