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ipad使用AVFoundation捕捉StillImage，图片比率问题

AVCaptureSession设置的是

AVCaptureSessionPresetPhoto，也就是New iPad摄像头最大分辨率2592*1936.但是capture得到的比率确实1936*2592.

这里描述了相同的问题:

http://stackoverflow.com/questions/6976213/why-does-capturing-images-with-avfoundation-give-me-480x640-images-when-the-pres

我参照http://blog.logichigh.com/2008/06/05/uiimage-fix/得到了解决

转换代码如下:

  1 UIImage *scaleAndRotateImage(UIImage *image)  
  2 {  
  3     int kMaxResolution = 2592; // Or whatever  
  4     
  5     CGImageRef imgRef = image.CGImage;  
  6     
  7     CGFloat width = CGImageGetWidth(imgRef);  
  8     CGFloat height = CGImageGetHeight(imgRef);  
  9     
 10     CGAffineTransform transform = CGAffineTransformIdentity;  
 11     CGRect bounds = CGRectMake(0, 0, width, height);  
 12     if (width > kMaxResolution || height > kMaxResolution) {  
 13         CGFloat ratio = width/height;  
 14         if (ratio > 1) {  
 15             bounds.size.width = kMaxResolution;  
 16             bounds.size.height = bounds.size.width / ratio;  
 17         }  
 18         else {  
 19             bounds.size.height = kMaxResolution;  
 20             bounds.size.width = bounds.size.height * ratio;  
 21         }  
 22     }  
 23     
 24     CGFloat scaleRatio = bounds.size.width / width;  
 25     CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));  
 26     CGFloat boundHeight;  
 27     UIImageOrientation orient = image.imageOrientation;  
 28     switch(orient) {  
 29             
 30         case UIImageOrientationUp: //EXIF = 1  
 31             transform = CGAffineTransformIdentity;  
 32             break;  
 33             
 34         case UIImageOrientationUpMirrored: //EXIF = 2  
 35             transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);  
 36             transform = CGAffineTransformScale(transform, -1.0, 1.0);  
 37             break;  
 38             
 39         case UIImageOrientationDown: //EXIF = 3  
 40             transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);  
 41             transform = CGAffineTransformRotate(transform, M_PI);  
 42             break;  
 43             
 44         case UIImageOrientationDownMirrored: //EXIF = 4  
 45             transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);  
 46             transform = CGAffineTransformScale(transform, 1.0, -1.0);  
 47             break;  
 48             
 49         case UIImageOrientationLeftMirrored: //EXIF = 5  
 50             boundHeight = bounds.size.height;  
 51             bounds.size.height = bounds.size.width;  
 52             bounds.size.width = boundHeight;  
 53             transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);  
 54             transform = CGAffineTransformScale(transform, -1.0, 1.0);  
 55             transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);  
 56             break;  
 57             
 58         case UIImageOrientationLeft: //EXIF = 6  
 59             boundHeight = bounds.size.height;  
 60             bounds.size.height = bounds.size.width;  
 61             bounds.size.width = boundHeight;  
 62             transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);  
 63             transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);  
 64             break;  
 65             
 66         case UIImageOrientationRightMirrored: //EXIF = 7  
 67             boundHeight = bounds.size.height;  
 68             bounds.size.height = bounds.size.width;  
 69             bounds.size.width = boundHeight;  
 70             transform = CGAffineTransformMakeScale(-1.0, 1.0);  
 71             transform = CGAffineTransformRotate(transform, M_PI / 2.0);  
 72             break;  
 73             
 74         case UIImageOrientationRight: //EXIF = 8  
 75             boundHeight = bounds.size.height;  
 76             bounds.size.height = bounds.size.width;  
 77             bounds.size.width = boundHeight;  
 78             transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);  
 79             transform = CGAffineTransformRotate(transform, M_PI / 2.0);  
 80             break;  
 81             
 82         default:  
 83             [NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"];  
 84             
 85     }  
 86     
 87     UIGraphicsBeginImageContext(bounds.size);  
 88     
 89     CGContextRef context = UIGraphicsGetCurrentContext();  
 90     
 91     if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {  
 92         CGContextScaleCTM(context, -scaleRatio, scaleRatio);  
 93         CGContextTranslateCTM(context, -height, 0);  
 94     }  
 95     else {  
 96         CGContextScaleCTM(context, scaleRatio, -scaleRatio);  
 97         CGContextTranslateCTM(context, 0, -height);  
 98     }  
 99     
100     CGContextConcatCTM(context, transform);  
101     
102     CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);  
103     UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();  
104     UIGraphicsEndImageContext();  
105     
106     return imageCopy;  
107 }

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原文地址：https://www.cnblogs.com/cokecoffe/p/2594736.html