image-decode.swift

override func viewDidLoad() {
    super.viewDidLoad()
    
        let url = URL(string: "https://external-preview.redd.it/nL7zG2Q2FkHwyJ15KgT4A7jk2R4cMddQpKb_Kx9YR8U.jpg?width=1080&crop=smart&auto=webp&s=91ee8327fdb33b3bb94cb0eab7e26221763e33f4")!
        
        URLSession.shared.dataTask(with: url) { data, response, error in
            print("Downloaded! Waiting…")
            
            DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(8)) {
                // Immediately spikes approximately 7 MB upon execution
                let newImage = data!.downsample()
                print(newImage)
            }
        }.resume()
    }
}

extension Data {
    func downsample() -> UIImage? {
        let imageSourceOptions = [kCGImageSourceShouldCache: false] as CFDictionary

        guard let imageSource = CGImageSourceCreateWithData(self as CFData, imageSourceOptions) else { return nil }

        let downsampleOptions = [
            kCGImageSourceCreateThumbnailFromImageAlways: true,
            kCGImageSourceShouldCacheImmediately: true,
            kCGImageSourceCreateThumbnailWithTransform: true,
            kCGImageSourceThumbnailMaxPixelSize: 700
        ] as CFDictionary
        
        guard let downsampledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, downsampleOptions) else { return nil }
        
        return UIImage(cgImage: downsampledImage)
    }
}