http://www.tuicool.com/articles/IfEZre

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今天寫demo的時候發現, 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, 則會把原圖片向又旋轉90度。

剛開始覺得莫名其妙, 不知所措。 后來百度了一下，找到了解決辦法。

ps: 查找過程中, 碰到了一種說法:

//get original photo from iOS photos //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];

至于是否正確, 還沒確定。 先Mark。

下面的解決辦法親測可行。 原文:http://www.cnblogs.com/jiangyazhou/archive/2012/03/22/2412343.html

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; }

轉載于:https://www.cnblogs.com/itlover2013/p/4957259.html

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