如果把通過相機獲取到的圖片，直接進行操作, 比如裁剪, 縮放, 則原圖片會向右旋轉90度。
//如果該圖片大于2M，會自動旋轉90度；否則不旋轉
UIImage* originalImg=[dict objectForKey:UIImagePickerControllerOriginalImage];
這種說法沒試過，不知道準不準確。
用相機拍攝出來的照片含有EXIF信息，UIImage的imageOrientation屬性指的就是EXIF中的orientation信息。
如果我們忽略orientation信息，而直接對照片進行像素處理或者drawInRect等操作，得到的結果是翻轉或者旋轉90之后的樣子。這是因為我們執行像素處理或者drawInRect等操作之后，imageOrientaion信息被刪除了，imageOrientaion被重設為0，造成照片內容和imageOrientaion不匹配。
所以，在對照片進行處理之前，先將照片旋轉到正確的方向，并且返回的imageOrientaion為0。
下面這個方法就是一個UIImage category中的方法，用它可以達到以上目的。
- (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;
}
