How to convert pixel dimension to CG Size in Swift? - swift

Question

I have large images uploaded by users in Swift and I need to resize them all to 100x100px to create thumbnails to store in my server. So far I have found that this resizes an image given a CGSize:
func resizedImage(image: UIImage, size: CGSize) -> UIImage? {
let renderer = UIGraphicsImageRenderer(size: size)
return renderer.image { (context) in
image.draw(in: CGRect(origin: .zero, size: size))
}
}
Is there any way to create a CGSize knowing that my target size is strictly 100x100px?

Answer 1

Got this to work:
extension UIImage {
func resizedImage(pixelSize: (width: Int, height: Int)) -> UIImage? {
var size = CGSize(width: CGFloat(pixelSize.width) / UIScreen.main.scale, height: CGFloat(pixelSize.height) / UIScreen.main.scale)
let rect = AVMakeRect(aspectRatio: self.size, insideRect: CGRect(x:0, y:0, width: size.width, height: size.height))
let renderer = UIGraphicsImageRenderer(size: size)
return renderer.image { (context) in
self.draw(in: rect)
}
}
}

Answer 2

You should initialize your render based on the user device scale and multiply its width and height instead of dividing it:
extension UIImage {
func aspectFitScaled(to size: CGSize) -> UIImage {
let format = imageRendererFormat
format.opaque = false
format.scale = UIScreen.main.scale
let isLandscape = self.size.width > self.size.height
let ratio = isLandscape ? size.width / self.size.width : size.height / self.size.height
let drawSize = self.size.scaled(by: ratio)
let x = (size.width - drawSize.width) / 2
let y = (size.height - drawSize.height) / 2
let origin = CGPoint(x: x, y: y)
return UIGraphicsImageRenderer(size: size, format: format).image { _ in
draw(in: CGRect(origin: origin, size: drawSize))
}
}
}
usage:
class ViewController: UIViewController {
// imageView frame is 200 x 200
#IBOutlet weak var imageView: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
// original image size is (719.0, 808.0)
let image = UIImage(data: try! Data(contentsOf: URL(string: "https://i.stack.imgur.com/Xs4RX.jpg")!))!
imageView.backgroundColor = .gray
let ivImage = image.aspectFitScaled(to: imageView.frame.size)
imageView.image = ivImage
print("ivImage.size", ivImage.size) // (200.0, 200.0)
print("ivImage.scale", ivImage.scale) // screen scale 3.0 iPhone 8 Plus
// lets check the real image dimension
let data = ivImage.jpegData(compressionQuality: 1)!
let savedSize = UIImage(data: data)!.size
print("savedSize", savedSize) // savedSize (600.0, 600.0)
}
}