Resizing CGImage in Swift 3

cgimage.swift

func resize(_ image: CGImage) -> CGImage? {
        var ratio: Float = 0.0
        let imageWidth = Float(image.width)
        let imageHeight = Float(image.height)
        let maxWidth: Float = 1024.0
        let maxHeight: Float = 768.0
        
        // Get ratio (landscape or portrait)
        if (imageWidth > imageHeight) {
            ratio = maxWidth / imageWidth
        } else {
            ratio = maxHeight / imageHeight
        }
        
        // Calculate new size based on the ratio
        if ratio > 1 {
            ratio = 1
        }
        
        let width = imageWidth * ratio
        let height = imageHeight * ratio
        
        guard let colorSpace = image.colorSpace else { return nil }
        guard let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: image.bitsPerComponent, bytesPerRow: image.bytesPerRow, space: colorSpace, bitmapInfo: image.alphaInfo.rawValue) else { return nil }
        
        // draw image to context (resizing it)
        context.interpolationQuality = .high
        context.draw(image, in: CGRect(x: 0, y: 0, width: Int(width), height: Int(height)))
        
        // extract resulting image from context
        return context.makeImage()

    }

lanczos.swift

let ciImage = CIImage(cgImage: image)

let filter = CIFilter(name: "CILanczosScaleTransform")!
filter.setValue(ciImage, forKey: "inputImage")
filter.setValue(ratio, forKey: "inputScale")
filter.setValue(1.0, forKey: "inputAspectRatio")
let outputImage = filter.value(forKey: "outputImage") as! CIImage

let context = CIContext(options: [kCIContextUseSoftwareRenderer: false])
return context.createCGImage(outputImage, from: outputImage.extent)

Just had a look at your resize function, but for me the CGContext (line 24) is always nil?!? Any ideas? I am running it on macOS

Same issue here

Why are you passing alphaInfo as bitmapInfo?

    if ratio > 1 {
        ratio = 1
    }
    
  what if ratio needed to be > 1?