extension UIImage {
 
 //UIKit
 func resizeUI(size: CGSize) -> UIImage? {
 
 let hasAlpha = false
 let scale: CGFloat = 0.0 // Automatically use scale factor of main screen
 
 /**
 創(chuàng)建一個圖片類型的上下文。調用UIGraphicsBeginImageContextWithOptions函數(shù)就可獲得用來處理圖片的圖形上下文。利用該上下文，你就可以在其上進行繪圖，并生成圖片
 
 size：表示所要創(chuàng)建的圖片的尺寸
 opaque：表示這個圖層是否完全透明，如果圖形完全不用透明最好設置為YES以優(yōu)化位圖的存儲，這樣可以讓圖層在渲染的時候效率更高
 scale：指定生成圖片的縮放因子，這個縮放因子與UIImage的scale屬性所指的含義是一致的。傳入0則表示讓圖片的縮放因子根據(jù)屏幕的分辨率而變化，所以我們得到的圖片不管是在單分辨率還是視網膜屏上看起來都會很好
 */
 UIGraphicsBeginImageContextWithOptions(size, !hasAlpha, scale)
 self.draw(in: CGRect(origin: .zero, size: size))
 
 let resizedImage = UIGraphicsGetImageFromCurrentImageContext()
 UIGraphicsEndImageContext()
 return resizedImage!
 }
}

extension UIImage {
 
 //CoreGraphics
 func resizeCG(size:CGSize) -> UIImage? {
 
 guard let cgImage = self.cgImage else { return nil }
 
 let bitsPerComponent = cgImage.bitsPerComponent
 let bytesPerRow = cgImage.bytesPerRow
 let colorSpace = cgImage.colorSpace
 let bitmapInfo = cgImage.bitmapInfo
 
 guard let context = CGContext(data: nil,
  width: Int(size.width),
  height: Int(size.height),
  bitsPerComponent: bitsPerComponent,
  bytesPerRow: bytesPerRow,
  space: colorSpace!,
  bitmapInfo: bitmapInfo.rawValue) else {
 return nil
 }
 
 context.interpolationQuality = .high
 
 context.draw(cgImage, in: CGRect(origin: .zero, size: size))
 
 let resizedImage = context.makeImage().flatMap {
 UIImage(cgImage: $0)
 }
 return resizedImage
 }
}

extension UIImage {
 
 //ImageIO
 func resizeIO(size:CGSize) -> UIImage? {
 
 guard let data = UIImagePNGRepresentation(self) else { return nil }
 
 let maxPixelSize = max(size.width, size.height)
 
 //let imageSource = CGImageSourceCreateWithURL(url, nil)
 guard let imageSource = CGImageSourceCreateWithData(data as CFData, nil) else { return nil }
 
 //kCGImageSourceThumbnailMaxPixelSize為生成縮略圖的大小。當設置為800，如果圖片本身大于800*600，則生成后圖片大小為800*600，如果源圖片為700*500，則生成圖片為800*500
 let options: [NSString: Any] = [
 kCGImageSourceThumbnailMaxPixelSize: maxPixelSize,
 kCGImageSourceCreateThumbnailFromImageAlways: true
 ]
 
 let resizedImage = CGImageSourceCreateImageAtIndex(imageSource, 0, options as CFDictionary).flatMap{
 UIImage(cgImage: $0)
 }
 return resizedImage
 }
}

extension UIImage {
 
 //CoreImage
 func resizeCI(size:CGSize) -> UIImage? {
 
 guard let cgImage = self.cgImage else { return nil }
 
 let scale = (Double)(size.width) / (Double)(self.size.width)
 
 let image = CIImage(cgImage: cgImage)
 
 let filter = CIFilter(name: "CILanczosScaleTransform")!
 filter.setValue(image, forKey: kCIInputImageKey)
 filter.setValue(NSNumber(value:scale), forKey: kCIInputScaleKey)
 filter.setValue(1.0, forKey:kCIInputAspectRatioKey)
 
 guard let outputImage = filter.value(forKey: kCIOutputImageKey) as? CIImage else { return nil}
 
 let context = CIContext(options: [kCIContextUseSoftwareRenderer: false])
 
 let resizedImage = context.createCGImage(outputImage, from: outputImage.extent).flatMap {
 UIImage(cgImage: $0)
 }
 return resizedImage
 }
}

extension UIImage {
 
 //vImage
 func resizeVI(size:CGSize) -> UIImage? {
 
 guard let cgImage = self.cgImage else { return nil }
 
 var format = vImage_CGImageFormat(bitsPerComponent: 8, bitsPerPixel: 32, colorSpace: nil,
  bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.first.rawValue),
  version: 0, decode: nil, renderingIntent: .defaultIntent)
 
 var sourceBuffer = vImage_Buffer()
 defer {
 free(sourceBuffer.data)
 }
 
 var error = vImageBuffer_InitWithCGImage(&sourceBuffer, &format, nil, cgImage, numericCast(kvImageNoFlags))
 guard error == kvImageNoError else { return nil }
 
 // create a destination buffer
 let scale = self.scale
 let destWidth = Int(size.width)
 let destHeight = Int(size.height)
 let bytesPerPixel = cgImage.bitsPerPixel / 8
 let destBytesPerRow = destWidth * bytesPerPixel
 
 let destData = UnsafeMutablePointer<UInt8>.allocate(capacity: destHeight * destBytesPerRow)
 defer {
 destData.deallocate(capacity: destHeight * destBytesPerRow)
 }
 var destBuffer = vImage_Buffer(data: destData, height: vImagePixelCount(destHeight), width: vImagePixelCount(destWidth), rowBytes: destBytesPerRow)
 
 // scale the image
 error = vImageScale_ARGB8888(&sourceBuffer, &destBuffer, nil, numericCast(kvImageHighQualityResampling))
 guard error == kvImageNoError else { return nil }
 
 // create a CGImage from vImage_Buffer
 var destCGImage = vImageCreateCGImageFromBuffer(&destBuffer, &format, nil, nil, numericCast(kvImageNoFlags), &error)?.takeRetainedValue()
 guard error == kvImageNoError else { return nil }
 
 // create a UIImage
 let resizedImage = destCGImage.flatMap {
 UIImage(cgImage: $0, scale: 0.0, orientation: self.imageOrientation)
 }
 
 destCGImage = nil
 return resizedImage
 }
}