别忽视UIImage中的方向属性, imageOrientation

这几天写个拍照,或者从相册中选择照片,进行剪切,然后分享.结果出现了,剪切后图片颠倒或者旋转90度的问题.

找了很久才发现是忽略imageOrientation这个属性.

以下为解决方法:

[cpp]  view plain copy

1. + (UIImage *)fixOrientation:(UIImage *)aImage {  
2.       
3.     // No-op if the orientation is already correct  
4.     if (aImage.imageOrientation == UIImageOrientationUp)   
5.         return aImage;  
6.       
7.     // We need to calculate the proper transformation to make the image upright.  
8.     // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.  
9.     CGAffineTransform transform = CGAffineTransformIdentity;  
10.       
11.     switch (aImage.imageOrientation) {  
12.         case UIImageOrientationDown:  
13.         case UIImageOrientationDownMirrored:  
14.             transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);  
15.             transform = CGAffineTransformRotate(transform, M_PI);  
16.             break;  
17.               
18.         case UIImageOrientationLeft:  
19.         case UIImageOrientationLeftMirrored:  
20.             transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);  
21.             transform = CGAffineTransformRotate(transform, M_PI_2);  
22.             break;  
23.               
24.         case UIImageOrientationRight:  
25.         case UIImageOrientationRightMirrored:  
26.             transform = CGAffineTransformTranslate(transform, 0, aImage.size.height);  
27.             transform = CGAffineTransformRotate(transform, -M_PI_2);  
28.             break;  
29.         default:  
30.             break;  
31.     }  
32.       
33.     switch (aImage.imageOrientation) {  
34.         case UIImageOrientationUpMirrored:  
35.         case UIImageOrientationDownMirrored:  
36.             transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);  
37.             transform = CGAffineTransformScale(transform, -1, 1);  
38.             break;  
39.               
40.         case UIImageOrientationLeftMirrored:  
41.         case UIImageOrientationRightMirrored:  
42.             transform = CGAffineTransformTranslate(transform, aImage.size.height, 0);  
43.             transform = CGAffineTransformScale(transform, -1, 1);  
44.             break;  
45.         default:  
46.             break;  
47.     }  
48.       
49.     // Now we draw the underlying CGImage into a new context, applying the transform  
50.     // calculated above.  
51.     CGContextRef ctx = CGBitmapContextCreate(NULL, aImage.size.width, aImage.size.height,  
52.                                              CGImageGetBitsPerComponent(aImage.CGImage), 0,  
53.                                              CGImageGetColorSpace(aImage.CGImage),  
54.                                              CGImageGetBitmapInfo(aImage.CGImage));  
55.     CGContextConcatCTM(ctx, transform);  
56.     switch (aImage.imageOrientation) {  
57.         case UIImageOrientationLeft:  
58.         case UIImageOrientationLeftMirrored:  
59.         case UIImageOrientationRight:  
60.         case UIImageOrientationRightMirrored:  
61.             // Grr...  
62.             CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.height,aImage.size.width), aImage.CGImage);  
63.             break;  
64.               
65.         default:  
66.             CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.width,aImage.size.height), aImage.CGImage);  
67.             break;  
68.     }  
69.       
70.     // And now we just create a new UIImage from the drawing context  
71.     CGImageRef cgimg = CGBitmapContextCreateImage(ctx);  
72.     UIImage *img = [UIImage imageWithCGImage:cgimg];  
73.     CGContextRelease(ctx);  
74.     CGImageRelease(cgimg);  
75.     return img;  
76. }  

参考:http://www.cnblogs.com/jiangyazhou/archive/2012/03/22/2412343.html

如果用用UIGraphicsBeginImageContext 去重新绘制也可以解决,但是处理速度实在太慢.