How to resize an UIImage while maintaining its Aspect Ratio - ios

Question

I want to resize a UIImage with maintaining its Aspect Ratio. I have written the following code, but it is not working as expected.
Code
-(UIImage * ) scaleImage: (UIImage * ) image toSize: (CGSize) targetSize {
CGFloat scaleFactor = 1.0;
if (image.size.width > targetSize.width || image.size.height > targetSize.height)
if (!((scaleFactor = (targetSize.width / image.size.width)) > (targetSize.height / image.size.height))) //scale to fit width, or
scaleFactor = targetSize.height / image.size.height; // scale to fit heigth.
UIGraphicsBeginImageContext(targetSize);
CGRect rect = CGRectMake((targetSize.width - image.size.width * scaleFactor) / 2, (targetSize.height - image.size.height * scaleFactor) / 2,
image.size.width * scaleFactor, image.size.height * scaleFactor);
[image drawInRect: rect];
UIImage * scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return scaledImage;
}
What exactly is wrong here?

Answer 1

I'm using something similar to this in a few projects:
- (UIImage*) scaleImage:(UIImage*)image toSize:(CGSize)newSize {
CGSize scaledSize = newSize;
float scaleFactor = 1.0;
if( image.size.width > image.size.height ) {
scaleFactor = image.size.width / image.size.height;
scaledSize.width = newSize.width;
scaledSize.height = newSize.height / scaleFactor;
}
else {
scaleFactor = image.size.height / image.size.width;
scaledSize.height = newSize.height;
scaledSize.width = newSize.width / scaleFactor;
}
UIGraphicsBeginImageContextWithOptions( scaledSize, NO, 0.0 );
CGRect scaledImageRect = CGRectMake( 0.0, 0.0, scaledSize.width, scaledSize.height );
[image drawInRect:scaledImageRect];
UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return scaledImage;
}

Answer 2

If this is for displaying in a UI, you can use Interface Builder and specify the "Aspect Fit" property.
You can also do this in code by setting the content mode to UIViewContentModeScaleAspectFit:
imageView.contentMode = UIViewContentModeScaleAspectFit;

Answer 3

This method takes an image and a max dimension. If the max original image dimension is less than the specified max dimension, you get the original back so it won't get blown up. Otherwise, you get a new image having a max dimension of the one specified and the other determined by the original aspect ratio. So as an example, if you give it a 1024x768 image and max dimension of 640 you get back a 640x480 version, if you give it a 768x1024 image and max dimension of 640 you get back a 480x640 version.
- (UIImage *)resizeImage:(UIImage *)image
withMaxDimension:(CGFloat)maxDimension
{
if (fmax(image.size.width, image.size.height) <= maxDimension) {
return image;
}
CGFloat aspect = image.size.width / image.size.height;
CGSize newSize;
if (image.size.width > image.size.height) {
newSize = CGSizeMake(maxDimension, maxDimension / aspect);
} else {
newSize = CGSizeMake(maxDimension * aspect, maxDimension);
}
UIGraphicsBeginImageContextWithOptions(newSize, NO, 1.0);
CGRect newImageRect = CGRectMake(0.0, 0.0, newSize.width, newSize.height);
[image drawInRect:newImageRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}

Answer 4

In my case (I wanted to have an image in a UIView) and keep the ratio with auto layout the way described here was great. The most important part of the article for me was (almost quoting):
constraint = [NSLayoutConstraint constraintWithItem:self.imageView
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:self.imageView
attribute:NSLayoutAttributeWidth
multiplier:ration
constant:0.0f];
[self.imageView addConstraint:constraint];
the only thing is to calculate the ratio according to the actual width and height of image. I found this way easy and elegant.

Answer 5

- (UIImage *)imageWithImage:(UIImage*)image scaledToSize:(CGSize)newSize {
UIGraphicsBeginImageContext(newSize);
float ratio = newSize.width/image.size.width;
[image drawInRect:CGRectMake(0, 0, newSize.width, ratio * image.size.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
NSLog(#"New Image Size : (%f, %f)", newImage.size.width, newImage.size.height);
UIGraphicsEndImageContext();
return newImage;
}

Answer 6

In Swift 5 you can use scaleAspectFit on the contentMode attribute.
let photo = UIImage(imageLiteralResourceName: "your_img_name")
let photoImageView = UIImageView(image: photo)
photoImageView.contentMode = .scaleAspectFit