iphone UIImage 如何生成缩略图

http://brian-erickson.com/uiimage-thumbnails-in-objective-c-for-the-iph

+ (UIImage *)generatePhotoThumbnail:(UIImage *)image {
	// Create a thumbnail version of the image for the event object.
	CGSize size = image.size;
	CGSize croppedSize;
	CGFloat ratio = 64.0;
	CGFloat offsetX = 0.0;
	CGFloat offsetY = 0.0;

	// check the size of the image, we want to make it 
	// a square with sides the size of the smallest dimension
	if (size.width > size.height) {
		offsetX = (size.height - size.width) / 2;
		croppedSize = CGSizeMake(size.height, size.height);
	} else {
		offsetY = (size.width - size.height) / 2;
		croppedSize = CGSizeMake(size.width, size.width);
	}

	// Crop the image before resize
	CGRect clippedRect = CGRectMake(offsetX * -1, offsetY * -1, croppedSize.width, croppedSize.height);
	CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], clippedRect);
	// Done cropping

	// Resize the image
	CGRect rect = CGRectMake(0.0, 0.0, ratio, ratio);

	UIGraphicsBeginImageContext(rect.size);
	[[UIImage imageWithCGImage:imageRef] drawInRect:rect];
	UIImage *thumbnail = UIGraphicsGetImageFromCurrentImageContext();
	UIGraphicsEndImageContext();
	// Done Resizing

	return thumbnail;
}

或者

http://vocaro.com/trevor/blog/2009/10/12/resize-a-uiimage-the-right-way/