图片旋转90度解决的方法

假设把通过相机获取到的图片，直接进行操作, 比方裁剪, 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:

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//get original photo from iOS photos

//假设该图片大于2M，会自己主动旋转90度；否则不旋转

UIImage* originalImg=[dict objectForKey:UIImagePickerControllerOriginalImage];

至于是否正确, 还没确定。

先Mark。

以下的解决的方法亲測可行。 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。

假设我们忽略orientation信息。而直接对比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。这是由于我们运行像素处理或者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。在对比片进行处理之前。先将照片旋转到正确的方向，而且返回的imageOrientaion为0。

以下这种方法就是一个UIImage category中的方法。用它能够达到以上目的。

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- (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;

}