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，这里主要用到Orientation属性。
Orientation属性说明如下：
下面就直接上代码了。
主要有html5页面和一个js，示例功能包含了图片压缩和旋转。
自己写的是uploadImage.js。
html5测试页面如下：
uploadImage.js如下：
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;
}
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
canvas.width = expectWidth;
canvas.height = expectHeight;
ctx.drawImage(this,expectWidth,expectHeight);
var base64 = null;
//修复ios
if (navigator.userAgent.match(/iphone/i)) {
console.log('iphone');
//alert(expectWidth + ',' + expectHeight);
//如果方向角不为1，都需要进行旋转 added by lzk
if(Orientation != "" && Orientation != 1){
alert('旋转处理');
switch(Orientation){
case 6://需要顺时针（向左）90度旋转
alert('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
alert('需要顺时针（向右）90度旋转');
rotateImg(this,'right',canvas);
break;
case 3://需要180度旋转
alert('需要180度旋转');
rotateImg(this,canvas);//转两次
rotateImg(this,canvas);
break;
}
}
/*var mpImg = new MegaPixImage(image);
mpImg.render(canvas,{
maxWidth: 800,maxHeight: 1200,quality: 0.8,orientation: 8
});*/
base64 = canvas.toDataURL("image/jpeg",0.8);
}else if (navigator.userAgent.match(/Android/i)) {// 修复android
var encoder = new JPEGEncoder();
base64 = encoder.encode(ctx.getImageData(0,expectHeight),80);
}else{
//alert(Orientation);
if(Orientation != "" && Orientation != 1){
//alert('旋转处理');
switch(Orientation){
case 6://需要顺时针（向左）90度旋转
alert('需要顺时针（向左）90度旋转');
rotateImg(this,canvas);
break;
}
}
base64 = canvas.toDataURL("image/jpeg",0.8);
}
//uploadImage(base64);
$("#myImage").attr("src",base64);
};
};
oReader.readAsDataURL(file); }
}
//对图片旋转处理 added by lzk
function rotateImg(img,direction,canvas) {
//alert(img);
//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;
//var img = document.getElementById(pid);
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 = img.getAttribute('step');
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 = maxstep);
}
//img.setAttribute('step',step);
/*var canvas = document.getElementById('pic' + pid);
if (canvas == null) {
img.style.display = 'none';
canvas = document.createElement('canvas');
canvas.setAttribute('id','pic_' + pid);
img.parentNode.appendChild(canvas);
} /
//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);
break;
case 1:
canvas.width = height;
canvas.height = width;
ctx.rotate(degree);
ctx.drawImage(img,-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,0);
break;
}
}
