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(gè)圖片類型的上下文。調(diào)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(jìn)行繪圖，并生成圖片
 
 size：表示所要?jiǎng)?chuàng)建的圖片的尺寸
 opaque：表示這個(gè)圖層是否完全透明，如果圖形完全不用透明最好設(shè)置為YES以優(yōu)化位圖的存儲(chǔ)，這樣可以讓圖層在渲染的時(shí)候效率更高
 scale：指定生成圖片的縮放因子，這個(gè)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(wǎng)膜屏上看起來都會(huì)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(dāng)設(shè)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
 }
}