IOS中测量和调整UIImage到指定CGSize

+(UIImage*)imageByScalingAndCroppingForSize:(UIImage*)selectedImage withTargetSize:(CGSize)size
{
//	if (selectedImage.size.width > selectedImage.size.height)
//	{
//		float height = (size.height * selectedImage.size.height) / selectedImage.size.width ;
//		size = CGSizeMake(size.width, height);
//	}
//	else
//	{
//		float width = (size.height * selectedImage.size.width) / selectedImage.size.height ;
//		size = CGSizeMake(width, size.width);
//	}
//	UIGraphicsBeginImageContext(size);
//	[selectedImage drawInRect:CGRectMake(0, 0, size.width, size.height) blendMode:kCGBlendModePlusDarker alpha:1];
//
//	UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
//	UIGraphicsEndImageContext();
//	return scaledImage;
UIImage *newImage = nil;
CGSize imageSize = selectedImage.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = size.width;
CGFloat targetHeight = size.height;
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

if (CGSizeEqualToSize(imageSize, size) == NO)
{
CGFloat widthFactor = targetWidth / width;
CGFloat heightFactor = targetHeight / height;

if (widthFactor > heightFactor)
scaleFactor = widthFactor; // scale to fit height
else
scaleFactor = heightFactor; // scale to fit width
scaledWidth  = width * scaleFactor;
scaledHeight = height * scaleFactor;

// center the image
if (widthFactor > heightFactor)
{
thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
}
else
if (widthFactor < heightFactor)
{
thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
}
}

UIGraphicsBeginImageContext(size); // this will crop

CGRect thumbnailRect = CGRectZero;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width  = scaledWidth;
thumbnailRect.size.height = scaledHeight;

[selectedImage drawInRect:thumbnailRect];

newImage = UIGraphicsGetImageFromCurrentImageContext();
if(newImage == nil)
//		NSLog(@"could not scale image");

//pop the context to get back to the default
UIGraphicsEndImageContext();
return newImage;

}