曾写过在前端把图片按比例压缩不失真上传服务器的前端和后台，可惜没有及时做总结保留代码，只记得js利用了base64位压缩和Exif.js进行图片处理，还有其中让我头疼的ios拍照上传后会倒置等诸多问题，当时也是在看了网上的各种代码后才有思路进行编写，希望留下一些大佬的代码在以后小弟我方便学习
<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta http-equiv="X-UA-Compatible" content="ie=edge"><title>Document</title>
</head><body><div><img src="imgzip.jpg" alt="" width="350"><img alt="" id="transform"></div><script>/*** 图片压缩，默认同比例压缩* @param {Object} path* pc端传入的路径可以为相对路径，但是在移动端上必须传入的路径是照相图片储存的绝对路径* @param {Object} obj* obj 对象 有 width， height， quality(0-1)* @param {Object} callback* 回调函数有一个参数，base64的字符串数据quality 图片缩放比例0-1 越大越清晰*/// 调用函数处理图片 dealImage("imgzip.jpeg", {// 注意：在pc端可以用绝对路径或相对路径，移动端最好用绝对路径// width: 1000,quality: 0.5}, function (base) {document.getElementById("transform").src = base;var mb = showSize(base);})function showSize(base64url) {//获取base64图片大小，返回字节var str = base64url.replace('data:image/png;base64,', '');var equalIndex = str.indexOf('=');if (str.indexOf('=') > 0) {str = str.substring(0, equalIndex);}var strLength = str.length;var fileLength = parseInt(strLength - (strLength / 8) * 2);console.log("压缩后的图片size", fileLength + "B")return fileLength;}function dealImage(path, obj, callback) {var img = new Image();img.src = path;img.onload = function () {var that = this;var ext = path.substring(path.lastIndexOf(".") + 1).toLowerCase();// 默认按比例压缩var w = that.width,h = that.height,scale = w / h;w = obj.width || w;h = obj.height || (w / scale);var quality = obj.quality; // 默认图片质量为0.7,可以为image/jpeg或image/webp类型的图片设置图片质量，取值0-1，超出则以默认值0.92替代//生成canvasvar canvas = document.createElement('canvas');var ctx = canvas.getContext('2d');// 创建属性节点var anw = document.createAttribute("width");anw.nodeValue = w;var anh = document.createAttribute("height");anh.nodeValue = h;canvas.setAttributeNode(anw);canvas.setAttributeNode(anh);ctx.drawImage(that, 0, 0, w, h);// 图像质量if (obj.quality && obj.quality <= 1 && obj.quality > 0) {quality = obj.quality;}// quality值越小，所绘制出的图像越模糊console.log("tup", ext)var base64 = canvas.toDataURL('image/jpeg', quality);// 回调函数返回base64的值callback(base64);}}</script>
</body></html>上传前不失真，有需要的去做按比例压缩（算法自己想）
html5+canvas进行移动端手机照片上传时，发现ios手机上传竖拍照片会逆时针旋转90度，横拍照片无此问题；Android手机没这个问题。
因此解决这个问题的思路是：获取到照片拍摄的方向角，对非横拍的ios照片进行角度旋转修正。
利用exif.js读取照片的拍摄信息，详见 http://code.ciaoca.com/javascript/exif-js/
这里主要用到Orientation属性。
Orientation属性说明如下：
旋转角度0° 参数1
顺时针90° 6
逆时针90° 8
180° 3
接下来的代码是大佬写的，我用于学习借鉴：
下面代码原链接：https://blog.csdn.net/linlzk/article/details/48654835
<!DOCTYPE html>
<html>
<head><meta charset="utf-8"><meta name="viewport" content="initial-scale=1.0, maximum-scale=1.0, user-scalable=no" /><title>图片上传</title><script type="text/javascript" src="js/jquery-1.8.3.js"></script><script type="text/javascript" src="js/uploadPicture/mobileBUGFix.mini.js" ></script><script type="text/javascript" src="js/uploadPicture/uploadImage.js" ></script><script type="text/javascript" src="js/exif.js" ></script>
</head>
<body><div style="height: 50px; line-height: 50px;text-align: center;border-bottom: 1px solid #171E28;">上传图片:<input type="file" accept="image/*" id="uploadImage" capture="camera" onchange="selectFileImage(this);" /></div><div style="margin-top: 10px;"><img alt="preview" src="" id="myImage"/></div>
</body>
</html>function selectFileImage(fileObj) {var file = fileObj.files['0'];//图片方向角 added by lzkvar Orientation = null;if (file) {console.log("正在上传,请稍后...");var rFilter = /^(image\/jpeg|image\/png)$/i; // 检查图片格式if (!rFilter.test(file.type)) {//showMyTips("请选择jpeg、png格式的图片", false);return;}// var URL = URL || webkitURL;//获取照片方向角属性，用户旋转控制EXIF.getData(file, function() {// alert(EXIF.pretty(this));EXIF.getAllTags(this);//alert(EXIF.getTag(this, 'Orientation'));Orientation = EXIF.getTag(this, 'Orientation');//return;});var oReader = new FileReader();oReader.onload = function(e) {//var blob = URL.createObjectURL(file);//_compress(blob, file, basePath);var image = new Image();image.src = e.target.result;image.onload = function() {var expectWidth = this.naturalWidth;var expectHeight = this.naturalHeight;if (this.naturalWidth > this.naturalHeight && this.naturalWidth > 800) {expectWidth = 800;expectHeight = expectWidth * this.naturalHeight / this.naturalWidth;} else if (this.naturalHeight > this.naturalWidth && this.naturalHeight > 1200) {expectHeight = 1200;expectWidth = expectHeight * this.naturalWidth / this.naturalHeight;}alert(expectWidth+','+expectHeight);var canvas = document.createElement("canvas");var ctx = canvas.getContext("2d");canvas.width = expectWidth;canvas.height = expectHeight;ctx.drawImage(this, 0, 0, expectWidth, expectHeight);alert(canvas.width+','+canvas.height);var base64 = null;var mpImg = new MegaPixImage(image);mpImg.render(canvas, {maxWidth: 800,maxHeight: 1200,quality: 0.8,orientation: Orientation});base64 = canvas.toDataURL("image/jpeg", 0.8);//uploadImage(base64);$("#myImage").attr("src", base64);};};oReader.readAsDataURL(file);}
}用到的第三方js文件：mobileBUGFix.mini.js
附上Exif.js说明
http://code.ciaoca.com/javascript/exif-js/