image_resize.swift

import UIKit
import Photos

private func imageWithImage(originImage:UIImage, targetSize:CGSize, contentMode: PHImageContentMode) -> UIImage {
    
  let originSize = CGSize(width: originImage.size.width * originImage.scale,
                          height: originImage.size.height * originImage.scale)
  let originRatio = originImage.size.width / originImage.size.height
  let targetSizeRatio = targetSize.width / targetSize.height
  var newSize: CGSize;
  
  if (targetSize.width >= originSize.width && targetSize.height >= originSize.height) {
    return originImage;
  }
  
  if ((originRatio*10).rounded() == (targetSizeRatio*10).rounded()) {
    if (targetSize.width > originSize.width) {
      return originImage
    } else {
      newSize = targetSize
    }
  } else if (targetSizeRatio > originRatio && contentMode == .aspectFit) {
    let height = min(originSize.height, targetSize.height)
    newSize = CGSize.init(width: originRatio * height, height: height)
  } else {
    let width = min(originSize.width, targetSize.width)
    newSize = CGSize.init(width: width, height: width / originRatio)
  }
  
  if #available(iOS 10.0, *) {
    let renderer = UIGraphicsImageRenderer(size: newSize)
    let newImage = renderer.image { _ in
      originImage.draw(in: CGRect.init(origin: CGPoint.zero, size: newSize))
    }
    return newImage.withRenderingMode(originImage.renderingMode)
  } else {
    UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0)
    originImage.draw(in: CGRect.init(origin: .zero, size: newSize))
    let newImage:UIImage = UIGraphicsGetImageFromCurrentImageContext() ?? originImage
    UIGraphicsEndImageContext()
    return newImage
  }
}


func test1() {
  let img = UIImage.init(named: "IMG_3118_copy.jpg")
  let newImage = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 50, height: 50), contentMode: .aspectFill);
  
  let newImage1 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 150, height: 50), contentMode: .aspectFill);


  let newImage2 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 5000, height: 5000), contentMode: .aspectFill);


  let newImage3 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 756/2, height: 1008/2), contentMode: .aspectFill);


  let newImage4 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 756*2, height: 1008*2), contentMode: .aspectFill);
}

test1()

func test2() {
  let img = UIImage.init(named: "IMG_3118_copy.jpg")
  let newImage = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 50, height: 50), contentMode: .aspectFit);
  
  let newImage1 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 150, height: 50), contentMode: .aspectFit);

  let newImage2 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 5000, height: 5000), contentMode: .aspectFit);


  let newImage3 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 756/2, height: 1008/2), contentMode: .aspectFit);


  let newImage4 = imageWithImage(originImage: img!, targetSize: CGSize.init(width: 756*2, height: 1008*2), contentMode: .aspectFit);
}

test2()