iOS scale image proportionally DEFAULT_PHOTO_MAX_SIZE - max size (height or width) of new image

gistfile1.m

+ (UIImage *)scaleImageProportionally:(UIImage *)image {

	if (MAX(image.size.height, image.size.width) <= DEFAULT_PHOTO_MAX_SIZE) {
		return image;
	}
	else {
		CGFloat targetWidth = 0;
		CGFloat targetHeight = 0;
		if (image.size.height > image.size.width) {
			CGFloat ratio = image.size.height / image.size.width;
			targetHeight = DEFAULT_PHOTO_MAX_SIZE;
			targetWidth = roundf(DEFAULT_PHOTO_MAX_SIZE/ ratio);
		}
		else {
			CGFloat ratio = image.size.width / image.size.height;
			targetWidth = DEFAULT_PHOTO_MAX_SIZE;
			targetHeight = roundf(DEFAULT_PHOTO_MAX_SIZE/ ratio);
		}

		CGSize targetSize = CGSizeMake(targetWidth, targetHeight);

		UIImage *sourceImage = image;
		UIImage *newImage = nil;

		CGSize imageSize = sourceImage.size;
		CGFloat width = imageSize.width;
		CGFloat height = imageSize.height;

		targetWidth = targetSize.width;
		targetHeight = targetSize.height;

		CGFloat scaleFactor = 0.0;
		CGFloat scaledWidth = targetWidth;
		CGFloat scaledHeight = targetHeight;

		CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);

		if (!CGSizeEqualToSize(imageSize, targetSize)) {

			CGFloat widthFactor = targetWidth / width;
			CGFloat heightFactor = targetHeight / height;

			if (widthFactor < heightFactor)
				scaleFactor = widthFactor;
			else
				scaleFactor = heightFactor;

			scaledWidth = roundf(width * scaleFactor);
			scaledHeight = roundf(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(targetSize);

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

		[sourceImage drawInRect:thumbnailRect];

		newImage = UIGraphicsGetImageFromCurrentImageContext();
		UIGraphicsEndImageContext();

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

		return newImage;
	}
}