[Swift] 이미지 크기 Resize 방법 세 가지

1. UIGraphicsBeginImageContextWithOptions

extension UIImage {
    func resize(targetSize: CGSize) -> UIImage? {
        let size = self.size
        let widthRatio  = targetSize.width  / size.width
        let heightRatio = targetSize.height / size.height
        let newSize = CGSize(width: size.width * min(widthRatio, heightRatio),
                             height: size.height * min(widthRatio, heightRatio))
        
        let rect = CGRect(origin: .zero, size: newSize)
        
        UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0)
        self.draw(in: rect)
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        return newImage
    }
}

 

2. UIGraphicsImageRenderer

extension UIImage {
    func resize(targetSize size: CGSize) -> UIImage? {
        let renderer = UIGraphicsImageRenderer(size: size)
        let image = renderer.image { _ in
            self.draw(in: CGRect(origin: .zero, size: size))
        }
        return image
    }
}

3. CGImageSourceCreateThumbnailAtIndex

extension UIImage {
    func resize(targetSize size: CGSize) -> UIImage? {
        guard let data = self.pngData() else { return nil }
        guard let source = CGImageSourceCreateWithData(data as CFData, nil) else { return nil }

        let options: [CFString: Any] = [
            kCGImageSourceThumbnailMaxPixelSize: max(size.width, size.height),
            kCGImageSourceCreateThumbnailFromImageAlways: true
        ]
        guard let cgImage = CGImageSourceCreateThumbnailAtIndex(source, 0, options as CFDictionary) else { return nil }

        return UIImage(cgImage: cgImage)
    }
}

 

각각의 차이에 대해서는 아래 블로그 참고

https://ios-development.tistory.com/1591

[iOS - swift] 7. Memory Deep Dive - 이미지 로드 매커니즘, 이미지 핸들링 최적화 (UIGraphicsBeginImageContextWit

https://ios-development.tistory.com/1592

[iOS - swift] 8. Memory Deep Dive - 이미지 리사이징, 이미지 다운 샘플링 (ImageIO, ImageSource)