Check out example codes for "swift set image size". It will help you in understanding the concepts better.

Code Example 1

extension UIImage {

    func imageResize (sizeChange:CGSize)-> UIImage{

        let hasAlpha = true
        let scale: CGFloat = 0.0 // Use scale factor of main screen

        UIGraphicsBeginImageContextWithOptions(sizeChange, !hasAlpha, scale)
        self.draw(in: CGRect(origin: CGPoint.zero, size: sizeChange))

        let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        return scaledImage!
    }

}

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