相机出照片是横着的

原因：用相机拍摄出来的照片含有EXIF信息，UIImage的imageOrientation属性指的就是EXIF中的orientation信息。

如果我们忽略orientation信息，而直接对照片进行像素处理或者drawInRect等操作，得到的结果是翻转或者旋转90之后的样子。这是因为我们执行像素处理或者drawInRect等操作之后，imageOrientaion信息被删除了，imageOrientaion被重设为0，造成照片内容和imageOrientaion不匹配。
所以，在对照片进行处理之前，先将照片旋转到正确的方向，并且返回的imageOrientaion为0。

代码实现：

+(UIImage )fixOrientation:(UIImage )aImage {
if (aImage.imageOrientation == UIImageOrientationUp)

  return aImage;
CGAffineTransform transform = CGAffineTransformIdentity;

switch (aImage.imageOrientation) {

  case UIImageOrientationDown:
  case UIImageOrientationDownMirrored:
      transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);
      transform = CGAffineTransformRotate(transform, M_PI);
      break;

  case UIImageOrientationLeft:
  case UIImageOrientationLeftMirrored:
      transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
      transform = CGAffineTransformRotate(transform, M_PI_2);
      break;

  case UIImageOrientationRight:
  case UIImageOrientationRightMirrored:
      transform = CGAffineTransformTranslate(transform, 0, aImage.size.height);
      transform = CGAffineTransformRotate(transform, -M_PI_2);
      break;
  default:
      break;
}

switch (aImage.imageOrientation) {

  case UIImageOrientationUpMirrored:
  case UIImageOrientationDownMirrored:
      transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
      transform = CGAffineTransformScale(transform, -1, 1);
      break;

  case UIImageOrientationLeftMirrored:
  case UIImageOrientationRightMirrored:
      transform = CGAffineTransformTranslate(transform, aImage.size.height, 0);
      transform = CGAffineTransformScale(transform, -1, 1);
      break;
  default:
      break;
}

CGContextRef ctx = CGBitmapContextCreate(NULL, aImage.size.width, aImage.size.height,

                                       CGImageGetBitsPerComponent(aImage.CGImage), 0,
                                       CGImageGetColorSpace(aImage.CGImage),
                                       CGImageGetBitmapInfo(aImage.CGImage));
CGContextConcatCTM(ctx, transform);
switch (aImage.imageOrientation) {

  case UIImageOrientationLeft:
  case UIImageOrientationLeftMirrored:
  case UIImageOrientationRight:
  case UIImageOrientationRightMirrored:
      // Grr...
      CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.height,aImage.size.width), aImage.CGImage);
      break;

  default:
      CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.width,aImage.size.height), aImage.CGImage);
      break;
}

CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
UIImage *img = [UIImage imageWithCGImage:cgimg];
CGContextRelease(ctx);
CGImageRelease(cgimg);
return img;
}

将image转90,180,270度的方法

原理:使用quartz2D来画图片，然后使用ctm变幻来实现旋转。

quartz2D的绘图左边和oc里面的绘图左边不一样，导致绘画出的图片是反转的。所以一上来得使它转正再进行进一步的旋转等

代码实现：

+ (UIImage *)image:(UIImage *)image rotation:(UIImageOrientation)orientation
{
    long double rotate = 0.0;
    CGRect rect;
    float translateX = 0;
    float translateY = 0;
    float scaleX = 1.0;
    float scaleY = 1.0;
    
    switch (orientation) {
        case UIImageOrientationLeft:
            rotate = M_PI_2;
            rect = CGRectMake(0, 0, image.size.height, image.size.width);
            translateX = 0;
            translateY = -rect.size.width;
            scaleY = rect.size.width/rect.size.height;
            scaleX = rect.size.height/rect.size.width;
            break;
        case UIImageOrientationRight:
            rotate = 3 * M_PI_2;
            rect = CGRectMake(0, 0, image.size.height, image.size.width);
            translateX = -rect.size.height;
            translateY = 0;
            scaleY = rect.size.width/rect.size.height;
            scaleX = rect.size.height/rect.size.width;
            break;
        case UIImageOrientationDown:
            rotate = M_PI;
            rect = CGRectMake(0, 0, image.size.width, image.size.height);
            translateX = -rect.size.width;
            translateY = -rect.size.height;
            break;
        default:
            rotate = 0.0;
            rect = CGRectMake(0, 0, image.size.width, image.size.height);
            translateX = 0;
            translateY = 0;
            break;
    }
    
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    //做CTM变换
    CGContextTranslateCTM(context, 0.0, rect.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextRotateCTM(context, rotate);
    CGContextTranslateCTM(context, translateX, translateY);
    
    CGContextScaleCTM(context, scaleX, scaleY);
    //绘制图片
    CGContextDrawImage(context, CGRectMake(0, 0, rect.size.width, rect.size.height), image.CGImage);
    
    UIImage *newPic = UIGraphicsGetImageFromCurrentImageContext();
    
    return newPic;
}

文章参考：
http://www.jianshu.com/p/6df4ecae0b28 http://blog.sina.com.cn/s/blog_6602ffbc0101ckx3.html

小小总结，不成敬意！