vImage를 사용한 이미지 리사이징 (가장 빠르고 정확)

UIImage+Extension.swift

extension UIImage {
    func resizeVI(size:CGSize) -> UIImage? {
        let cgImage = self.CGImage!
            
            var format = vImage_CGImageFormat(bitsPerComponent: 8, bitsPerPixel: 32, colorSpace: nil,
                                              bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.First.rawValue),
                                              version: 0, decode: nil, renderingIntent: CGColorRenderingIntent.RenderingIntentDefault)
            var sourceBuffer = vImage_Buffer()
            defer {
                sourceBuffer.data.dealloc(Int(sourceBuffer.height) * Int(sourceBuffer.height) * 4)
            }
            
            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 = CGImageGetBitsPerPixel(self.CGImage) / 8
            let destBytesPerRow = destWidth * bytesPerPixel
            let destData = UnsafeMutablePointer<UInt8>.alloc(destHeight * destBytesPerRow)
            defer {
                destData.dealloc(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
            let 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) }
            return resizedImage
    }
}