UIImageJpgRepresentation doubles image resolution - ios

Question

I am trying to save an image coming from the iPhone camera to a file. I use the following code:
try UIImageJPEGRepresentation(toWrite, 0.8)?.write(to: tempURL, options: NSData.WritingOptions.atomicWrite)
This results in a file double the resolution of the toWrite UIImage. I confirmed in the watch expressions that creating a new UIImage from UIImageJPEGRepresentation doubles its resolution
-> toWrite.size CGSize (width = 3264, height = 2448)
-> UIImage(data: UIImageJPEGRepresentation(toWrite, 0.8)).size CGSize? (width = 6528, height = 4896)
Any idea why this would happen, and how to avoid it?
Thanks

Answer 1

Your initial image has scale factor = 2, but when you init your image from data you will get image with scale factor = 1. Your way to solve it is to control the scale and init the image with scale property:
#available(iOS 6.0, *)
public init?(data: Data, scale: CGFloat)
Playground code that represents the way you can set scale
extension UIImage {
class func with(color: UIColor, size: CGSize) -> UIImage? {
let rect = CGRect(origin: .zero, size: size)
UIGraphicsBeginImageContextWithOptions(size, true, 2.0)
guard let context = UIGraphicsGetCurrentContext() else { return nil }
context.setFillColor(color.cgColor)
context.fill(rect)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return image
}
}
let image = UIImage.with(color: UIColor.orange, size: CGSize(width: 100, height: 100))
if let image = image {
let scale = image.scale
if let data = UIImageJPEGRepresentation(image, 0.8) {
if let newImage = UIImage(data: data, scale: scale) {
debugPrint(newImage?.size)
}
}
}