How to scale a UIImageView proportionally?

I have a UIImageView and the objective is to scale it down proportionally by giving it either a height or width.

UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://farm4.static.flickr.com/3092/2915896504_a88b69c9de.jpg"]]];
UIImageView *imageView = [[UIImageView alloc] initWithImage:image];	

//Add image view
[self.view addSubview:imageView];	

//set contentMode to scale aspect to fit
imageView.contentMode = UIViewContentModeScaleAspectFit;

//change width of frame
CGRect frame = imageView.frame;
frame.size.width = 100;
imageView.frame = frame;

The image did get resized but the position is not at the top left. What is the best approach to scaling image/imageView and how do I correct the position?

Fixed easily, once I found the documentation!

 imageView.contentMode = .scaleAspectFit

I've seen a bit of conversation about scale types so I decided to put together an article regarding some of the most popular content mode scaling types.

The associated image is here:

I just tried this, and UIImage does not support _imageScaledToSize.

I ended up adding a method to UIImage using a category - a suggestion I found on the Apple Dev forums.

In a project-wide .h -

@interface UIImage (Extras)
- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize;
@end;

Implementation:

@implementation UIImage (Extras)

- (UIImage *)imageByScalingProportionallyToSize:(CGSize)targetSize {

	UIImage *sourceImage = self;
	UIImage *newImage = nil;
	
	CGSize imageSize = sourceImage.size;
	CGFloat width = imageSize.width;
	CGFloat height = imageSize.height;
	
	CGFloat targetWidth = targetSize.width;
	CGFloat targetHeight = targetSize.height;
	
	CGFloat scaleFactor = 0.0;
	CGFloat scaledWidth = targetWidth;
	CGFloat scaledHeight = targetHeight;
	
	CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
	
	if (CGSizeEqualToSize(imageSize, targetSize) == NO) {
		
		CGFloat widthFactor = targetWidth / width;
		CGFloat heightFactor = targetHeight / height;
		
		if (widthFactor < heightFactor) 
			scaleFactor = widthFactor;
		else
			scaleFactor = heightFactor;
		
		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;
		}
	}
	
	
	// this is actually the interesting part:
	
	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 ;
}

@end;

imageView.contentMode = UIViewContentModeScaleAspectFill;
imageView.clipsToBounds = YES;

You could try making the imageView size match the image. The following code is not tested.

CGSize kMaxImageViewSize = {.width = 100, .height = 100};
CGSize imageSize = image.size;
CGFloat aspectRatio = imageSize.width / imageSize.height;
CGRect frame = imageView.frame;
if (kMaxImageViewSize.width / aspectRatio <= kMaxImageViewSize.height) 
{
    frame.size.width = kMaxImageViewSize.width;
    frame.size.height = frame.size.width / aspectRatio;
} 
else 
{
    frame.size.height = kMaxImageViewSize.height;
    frame.size.width = frame.size.height * aspectRatio;
}
imageView.frame = frame;

This works fine for me Swift 2.x:

imageView.contentMode = .ScaleAspectFill
imageView.clipsToBounds = true;

one can resize an UIImage this way

image = [UIImage imageWithCGImage:[image CGImage] scale:2.0 orientation:UIImageOrientationUp];

UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://farm4.static.flickr.com/3092/2915896504_a88b69c9de.jpg"]]];
UIImageView *imageView = [[UIImageView alloc] initWithImage:image]; 


//set contentMode to scale aspect to fit
imageView.contentMode = UIViewContentModeScaleAspectFit;

//change width of frame
//CGRect frame = imageView.frame;
//frame.size.width = 100;
//imageView.frame = frame;

//original lines that deal with frame commented out, yo.
imageView.frame = CGRectMake(10, 20, 60, 60);

...

//Add image view
[myView addSubview:imageView]; 

The original code posted at the top worked well for me in iOS 4.2.

I found that creating a CGRect and specifying all the top, left, width, and height values was the easiest way to adjust the position in my case, which was using a UIImageView inside a table cell. (Still need to add code to release objects)

Set your ImageView by selecting Mode to Aspect Fill and check the Clip Subviews box.

Set your UIimageview by scale.........

For Swift :

self.imageViews.contentMode = UIViewContentMode.ScaleToFill

UIImageView+Scale.h:

#import <Foundation/Foundation.h>

@interface UIImageView (Scale)

-(void) scaleAspectFit:(CGFloat) scaleFactor;

@end

UIImageView+Scale.m:

#import "UIImageView+Scale.h"

@implementation UIImageView (Scale)


-(void) scaleAspectFit:(CGFloat) scaleFactor{

    self.contentScaleFactor = scaleFactor;
    self.transform = CGAffineTransformMakeScale(scaleFactor, scaleFactor);

    CGRect newRect = self.frame;
    newRect.origin.x = 0;
    newRect.origin.y = 0;
    self.frame = newRect;
}

@end

If the solutions proposed here aren't working for you, and your image asset is actually a PDF, note that XCode actually treats PDFs differently than image files. In particular, it doesn't seem able to scale to fill properly with a PDF: it ends up tiled instead. This drove me crazy until I figured out that the issue was the PDF format. Convert to JPG and you should be good to go.

I used following code.where imageCoverView is UIView holds UIImageView

if (image.size.height<self.imageCoverView.bounds.size.height && image.size.width<self.imageCoverView.bounds.size.width)
{
    [self.profileImageView sizeToFit];
    self.profileImageView.contentMode =UIViewContentModeCenter
}
else
{
    self.profileImageView.contentMode =UIViewContentModeScaleAspectFit;
}

Usually I use this method for my apps (Swift 2.x compatible):

// Resize UIImage
func resizeImage(image:UIImage, scaleX:CGFloat,scaleY:CGFloat) ->UIImage {
    let size = CGSizeApplyAffineTransform(image.size, CGAffineTransformMakeScale(scaleX, scaleY))
    let hasAlpha = true
    let scale: CGFloat = 0.0 // Automatically use scale factor of main screen
    
    UIGraphicsBeginImageContextWithOptions(size, !hasAlpha, scale)
    image.drawInRect(CGRect(origin: CGPointZero, size: size))
    
    let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return scaledImage
}

I think you can do something like

image.center = [[imageView window] center];

Here is how you can scale it easily.

This works in 2.x with the Simulator and the iPhone.

UIImage *thumbnail = [originalImage _imageScaledToSize:CGSizeMake(40.0, 40.0) interpolationQuality:1];