+ (UIImage *)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;

}

修正图片方向