How to resize an UIImage based on device size and scale?

Question

I've an UIImage of size (1008, 669) how can I resize it based on my device size (so for eg if I'm viewing this in iPhone4s its width will be 640 x 960 ((320 * retina_scale) x (480 * retina_scale)). I'm using below method to do so, but my image just stretched in UIImageView . How to handle this? How to make it dynamic so that it'll work will all kind of images?

- (UIImage *) hResizeImage:(UIImage *)image withTargetSize:(CGSize)targetSize {
    CGSize size = image.size;
    CGFloat widthRatio = targetSize.width / image.size.width;
    CGFloat heightRatio = targetSize.height / image.size.height;

    // Figure out what our orientation is, and use that to form the rectangle
    CGSize newSize;
    if(widthRatio > heightRatio) {
        newSize = CGSizeMake(size.width * heightRatio, size.height * heightRatio);
    } else {
        newSize = CGSizeMake(size.width * widthRatio,  size.height * widthRatio);
    }

    // This is the rect that we've calculated out and this is what is actually used below
    CGRect scaledRect = CGRectMake(0, 0, newSize.width * [UIScreen mainScreen].scale, newSize.height * [UIScreen mainScreen].scale);

    // Actually do the resizing to the rect using the ImageContext stuff
    UIGraphicsBeginImageContextWithOptions(scaledRect.size, false, [UIScreen mainScreen].scale);
    [image drawInRect:scaledRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

Answer 1

Since the scale factor is specified in UIGraphicsBeginImageContextWithOptions, it is not needed to multiply the width and height by the screen scale when scaledRect is calculated.

And If you specify a value of 0.0 in UIGraphicsBeginImageContextWithOptions, the scale factor is automatically set to the scale factor of the device's main screen.

- (UIImage *)hResizeImage:(UIImage *)image withTargetSize:(CGSize)targetSize {
    CGSize size = image.size;
    CGFloat widthRatio = targetSize.width / image.size.width;
    CGFloat heightRatio = targetSize.height / image.size.height;

    // Figure out what our orientation is, and use that to form the rectangle
    CGSize newSize;
    if(widthRatio > heightRatio) {
        newSize = CGSizeMake(size.width * heightRatio, size.height * heightRatio);
    } else {
        newSize = CGSizeMake(size.width * widthRatio,  size.height * widthRatio);
    }

    // This is the rect that we've calculated out and this is what is actually used below
    CGRect scaledRect = CGRectMake(0, 0, newSize.width, newSize.height);

    // Actually do the resizing to the rect using the ImageContext stuff
    UIGraphicsBeginImageContextWithOptions(scaledRect.size, false, 0.0f);
    [image drawInRect:scaledRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}