Convert UIImage to grayscale keeping image quality

Question

I have this extension (found in obj-c and I converted it to Swift3) to get the same UIImage but grayscaled:

public fun         


        

Answer 1

I'd use CoreImage, which may keep the quality.

func convertImageToBW(image:UIImage) -> UIImage {

    let filter = CIFilter(name: "CIPhotoEffectMono")

    // convert UIImage to CIImage and set as input

    let ciInput = CIImage(image: image)
    filter?.setValue(ciInput, forKey: "inputImage")

    // get output CIImage, render as CGImage first to retain proper UIImage scale

    let ciOutput = filter?.outputImage
    let ciContext = CIContext()
    let cgImage = ciContext.createCGImage(ciOutput!, from: (ciOutput?.extent)!)

    return UIImage(cgImage: cgImage!)
}

Depending on how you use this code, you may want to create the CIContext outside of it for performance reasons.