UIImage+Downsampling.swift

        let url = Bundle.main.url(forResource: "cat1", withExtension: "jpg")!
        
        let size: CGSize = CGSize(width: 60, height: 90)
        let scale = UIScreen.main.scale
        
        // Bind the URL to the object without decoding (will not use memory yet).
        let options = [kCGImageSourceShouldCache:false] as CFDictionary
        let source = CGImageSourceCreateWithURL(url as CFURL, options)        
        
        let dimension = max(size.width, size.height) * scale
        let downsamplingOptions = [
            kCGImageSourceCreateThumbnailFromImageAlways: true,
            // CoreGraphics decode/cache the data into image memory
            // buffer when `CGImageSourceCreateThumbnailAtIndex(...)` called.
            kCGImageSourceShouldCacheImmediately: true,
            kCGImageSourceCreateThumbnailWithTransform: true,
            kCGImageSourceThumbnailMaxPixelSize: dimension
        ] as CFDictionary
        
        let image = CGImageSourceCreateThumbnailAtIndex(source!, 0, downsamplingOptions)!