downsample.swift

func downsampledImage(at url: URL, to size: CGSize, scale: CGFloat) -> UIImage? {    
    guard let imageResource = CGImageSourceCreateWithURL(url as CFURL, [kCGImageSourceShouldCache: false] as CFDictionary) else { return nil }
    let maxDimensionPixels = max(size.height, size.width) * scale
    let options = [
        kCGImageSourceShouldCacheImmediately: true,
        kCGImageSourceCreateThumbnailWithTransform: true,
        kCGImageSourceCreateThumbnailFromImageAlways: true,
        kCGImageSourceThumbnailMaxPixelSize: maxDimensionPixels
    ] as CFDictionary

    guard let cgImage = CGImageSourceCreateThumbnailAtIndex(imageResource, 0, options) else { return nil }
    return UIImage(cgImage: cgImage)
}