Iphone 裁剪图像后图像是否模糊？

我有一个应用程序，其中我正在裁剪从相机拍摄的图像。一切都进行得很顺利。但裁剪后的图像似乎模糊和拉伸

CGRect rect = CGRectMake(20,40,280,200);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();

// translated rectangle for drawing sub image 
CGRect drawRect = CGRectMake(-rect.origin.x, -rect.origin.y,280,200);

// clip to the bounds of the image context
// not strictly necessary as it will get clipped anyway?
CGContextClipToRect(context, CGRectMake(0, 0, rect.size.width, rect.size.height));

// draw image
[image drawInRect:drawRect];

// grab image
UIImage* croppedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGSize size = [croppedImage size];
NSLog(@" = %@",NSStringFromCGSize(size));
NSData* pictureData = UIImagePNGRepresentation(croppedImage);

有人能帮我找出哪里出了问题吗？

试着替换一下

UIGraphicsBeginImageContext(rect.size);

与

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要解释视网膜

你是指这个还是这个？你能提供一个屏幕截图吗？请检查这个：-但它给了我两倍大小的图像。例如（560400）图像。

UIGraphicsBeginImageContextWithOptions(rect.size, NO, [[UIScreen mainScreen] scale]);