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。

• 下面这个方法就是一个UIImage category中的方法，用它可以达到以上目的。

//绘制圆角
- (UIImage *)jx_drawRectWithRoundedCorner:(CGFloat)radius toSize:(CGSize)size
{
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    
    UIGraphicsBeginImageContextWithOptions(rect.size, false, [UIScreen mainScreen].scale);
    CGContextAddPath(UIGraphicsGetCurrentContext(), [[UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:UIRectCornerAllCorners cornerRadii:CGSizeMake(radius, radius )] CGPath]);
    
    CGContextClip(UIGraphicsGetCurrentContext());
    
    [self drawInRect:rect];
    CGContextDrawPath(UIGraphicsGetCurrentContext(), kCGPathFillStroke);
    UIImage *output = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return output;
}

//相册调用旋转90°
- (UIImage *)jx_rotatImageWithRadius:(NSInteger)radius
{
    if (radius > 0) {
        if (radius == 90) {
            // Rigth
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:self.scale orientation:UIImageOrientationRight];
        }else if(radius == 180){
            // Down
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:self.scale orientation:UIImageOrientationDown];
        }else if(radius == 270){
            // Left
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:1.0 orientation:UIImageOrientationLeft];
        }else{
            // Up
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:1.0 orientation:UIImageOrientationUp];
        }
    }
    else
    {
        radius = ABS(radius);
        if (radius == 90) {
            // Left
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:1.0 orientation:UIImageOrientationLeft];
        }else if(radius == 180){
            // Down
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:1.0 orientation:UIImageOrientationDown];
            
        }else if(radius == 270){
            // Right
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:1.0 orientation:UIImageOrientationRight];
        }else{
            // Up
            return [[UIImage alloc] initWithCGImage:self.CGImage scale:1.0 orientation:UIImageOrientationUp];
        }
    }
}

////相机调用旋转90°
+ (UIImage *)jx_fixOrientation:(UIImage *)aImage {
    
    // No-op if the orientation is already correct
    if (aImage.imageOrientation == UIImageOrientationUp)
        return aImage;
    
    // We need to calculate the proper transformation to make the image upright.
    // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
    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;
    }
    
    // Now we draw the underlying CGImage into a new context, applying the transform
    // calculated above.
    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;
    }
    
    // And now we just create a new UIImage from the drawing context
    CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
    UIImage *img = [UIImage imageWithCGImage:cgimg];
    CGContextRelease(ctx);
    CGImageRelease(cgimg);
    return img;
}