如果把通过相机获取到的图片，直接进行操作, 比如裁剪, 缩放, 则会把原图片向又旋转90度。
ps: 查找过程中, 碰到了一种说法:
- //get original photo from iOS photos
- //如果该图片大于2M，会自动旋转90度；否则不旋转
- UIImage* originalImg=[dict objectForKey:UIImagePickerControllerOriginalImage];
至于是否正确, 还没确定。 先Mark。
下面的解决办法亲测可行。 原文:http://www.cnblogs.com/jiangyazhou/archive/2012/03/22/2412343.html
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。
- - (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;
- }
