I have been doing some tests with the code to DownSampling / Scaling Image an Image from WWDC18 Session 416 iOS Memory Deep Dive.In this session they said that: - "Memory use if related the DIMENSION of the image, NOT file size.” - UIImage is expensive for sizing and resizing (will decompress memory first, internal coordinate space transforms are expensive) - Use ImageIO, it will work with out dirty memory (also API is faster)For my tests I used High Resolution Images with dimensions:1920 × 1080, 2560 × 1600, 3840 × 2160, 2560 × 1600, 4712 × 3133, 2560 × 1600 and 3072 × 2048.The following is the code that I used.import UIKit
struct ImageConverter{
static func resize(image: UIImage)-> UIImage{
let size = CGSize(width: 300, height: 300)
let renderer = UIGraphicsImageRenderer(size: size)
let resizedImage = renderer.image { context in
image.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
}
return resizedImage
}
}import UIKit
import ImageIO
struct ImageIOConverter{
static func resize(url: URL)-> UIImage{
guard let imageSource = CGImageSourceCreateWithURL(url as CFURL, nil) else {
fatalError("Can not get imageSource")
}
let options: [NSString: Any] = [
kCGImageSourceThumbnailMaxPixelSize: 300,
kCGImageSourceCreateThumbnailFromImageAlways: true
]
guard let scaledImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, options as CFDictionary) else {
fatalError("Can not get scaledImage")
}
return UIImage(cgImage: scaledImage)
}
}import UIKit
class ViewController: UIViewController {
@IBOutlet weak var imageView: UIImageView! // Constraints Width: 300, Height: 300
let resource = "1"
let ext = ".jpg"
var imageNamed : String {
return resource + ext
}
@IBAction func uploadOriginalImage(_ sender: Any) {
guard let image = UIImage(named: imageNamed) else {
fatalError("Can not get image")
}
imageView.image = image
}
@IBAction func uploadImageScaledUsingUIImage(_ sender: Any) {
guard let image = UIImage(named: imageNamed) else {
fatalError("Can not get image")
}
imageView.image = ImageConverter.resize(image: image)
}
@IBAction func uploadImageUsingImageIO(_ sender: Any) {
guard let url = Bundle.main.url(forResource:resource, withExtension: ext) else {
fatalError("Can not get image url")
}
imageView.image = ImageIOConverter.resize(url: url)
}
}Effectively, I found that with ImageIO, the amount of memory is smaller, but at the same time I also noticed that using ImageIO the final image look to have lower quality than using UIImage.I mean, using UIImage the final image looks more to the original image than using ImageIO.I wonder if, Is this the expected result? (Lower image quality but also lower memory).
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