原文链接：http://blog.csdn.net/sharpyl/article/details/53855948
今天开发一个拍照获取照片的功能的时候, 发现上传之后图片会自动旋转90.
测试发现, 只要是图片大于2M, 系统就会自动翻转照片
相机拍照后直接取出来的UIimage（用UIImagePickerControllerOriginalImage取出），它本身的imageOrientation属性是3，即UIImageOrientationRight。如果这个图片直接使用则没事，但是如果对它进行裁剪、缩放等操作后，它的这个imageOrientation属性会变成0。此时这张图片用在别的地方就会发生旋转。imageOrientation是只读的，不能直接修改其值。
解决方法如下:
1. 设置相机的一个属性allowsEditing为YES，设了这个值，你拍完照片后会在照片上出现一个框框，这就是对照片的裁剪编辑。在相机的代理方法中取照片的时候就别用UIImagePickerControllerOriginalImage来取了，要用UIImagePickerControllerEditedImage。用这个key取出来的照片，它的imageOrientation是0，所以之后的任何裁剪、缩放操作都不会造成旋转。这是第一种方法。
2. 第一种解决方法基本没用, 开发中基本都会对图片进行裁剪和压缩. 这里有一个专门针对这个事的很好的category
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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) {
caseUIImageOrientationDown:
caseUIImageOrientationDownMirrored:
transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);
transform = CGAffineTransformRotate(transform, M_PI);
break
;
caseUIImageOrientationLeft:
caseUIImageOrientationLeftMirrored:
transform = CGAffineTransformTranslate(transform, aImage.size.width,
0
);
transform = CGAffineTransformRotate(transform, M_PI_2);
break
;
caseUIImageOrientationRight:
caseUIImageOrientationRightMirrored:
transform = CGAffineTransformTranslate(transform,
0
, aImage.size.height);
transform = CGAffineTransformRotate(transform, -M_PI_2);
break
;
default
:
break
;
}
switch
(aImage.imageOrientation) {
caseUIImageOrientationUpMirrored:
caseUIImageOrientationDownMirrored:
transform = CGAffineTransformTranslate(transform, aImage.size.width,
0
);
transform = CGAffineTransformScale(transform, -
1
,
1
);
break
;
caseUIImageOrientationLeftMirrored:
caseUIImageOrientationRightMirrored:
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) {
caseUIImageOrientationLeft:
caseUIImageOrientationLeftMirrored:
caseUIImageOrientationRight:
caseUIImageOrientationRightMirrored:
// 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 = [UIImageimageWithCGImage:cgimg];
CGContextRelease(ctx);
CGImageRelease(cgimg);
return
img;
}
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