手机拍照上传到服务器时自动旋转

//使用前确保已经引入exif.js。下载地址：http://code.ciaoca.com/javascript/exif-js/
var file=document.getElementById('imagefile').files[0];//获取文件流
correcctImageOrientation(file);//调用方法，将图片修正。
// 纠正图片旋转方向
function correcctImageOrientation(file) {
    var Orientation = null;
    if (file) {
        var rFilter = /^(image/jpeg|image/png)$/i; // 检查图片格式
        if (!rFilter.test(file.type)) {
            return;
        }
        // 获取照片方向角属性，用户旋转控制
        EXIF.getData(file, function() {
            EXIF.getAllTags(this);
            Orientation = EXIF.getTag(this, 'Orientation');//获取图片旋转弧度
        });
        var oReader = new FileReader();
        oReader.onload = function(e) {
            var image = new Image();
            image.src = e.target.result;
            image.onload = function() {
                var expectWidth = this.naturalWidth;
                var expectHeight = this.naturalHeight;
                // 压缩图片。最大宽800，最大高1200
                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;
                }
                // 绘制canvas
                var canvas = document.createElement("canvas");
                var ctx = canvas.getContext("2d");
                canvas.width = expectWidth;
                canvas.height = expectHeight;
                ctx.drawImage(this, 0, 0, expectWidth, expectHeight);
                // base64 字符串
                var base64 = null;
                if(Orientation != "" && Orientation != 1){
                    switch(Orientation){
                        case 6:
                            // 需要顺时针（向左）90度旋转
                            rotateImg(this,'left',canvas);
                            break;
                        case 8:
                            //需要逆时针（向右）90度旋转
                            rotateImg(this,'right',canvas);
                            break;
                        case 3:
                            //需要180度旋转
                            rotateImg(this,'right',canvas);//转两次
                            rotateImg(this,'right',canvas);
                            break;
                    }
                }
                base64 = canvas.toDataURL("image/jpeg", 0.8);
                // 用base64回显
                var myImageList = $('.myImage');
                var len = $('.myImage').length;
                $('#myImg').attr("src", base64);//将处理好的图片流放到对应的元素中显示
            };
        };
        oReader.readAsDataURL(file);
    }
}

// 对图片旋转处理
function rotateImg(img, direction,canvas) {
    // 最小与最大旋转方向，图片旋转4次后回到原方向
    var min_step = 0;
    var max_step = 3;
    if (img == null)return;
    // img的高度和宽度不能在img元素隐藏后获取，否则会出错
    var height = img.height;
    var width = img.width;
    var step = 2;
    if (step == null) {
        step = min_step;
    }
    if (direction == 'right') {
        step++;
        // 旋转到原位置，即超过最大值
        step > max_step && (step = min_step);
    } else {
        step--;
        step < min_step && (step = max_step);
    }
    // 旋转角度以弧度值为参数
    var degree = step * 90 * Math.PI / 180;
    var ctx = canvas.getContext('2d');
    switch (step) {
        case 0:
            canvas.width = width;
            canvas.height = height;
            ctx.drawImage(img, 0, 0);
            break;
        case 1:
            canvas.width = height;
            canvas.height = width;
            ctx.rotate(degree);
            ctx.drawImage(img, 0, -height);
            break;
        case 2:
            canvas.width = width;
            canvas.height = height;
            ctx.rotate(degree);
            ctx.drawImage(img, -width, -height);
            break;
        case 3:
            canvas.width = height;
            canvas.height = width;
            ctx.rotate(degree);
            ctx.drawImage(img, -width, 0);
            break;
    }
}