Getting a CGImage from CIImage

Swift 3, Swift 4 and Swift 5

Here is a nice little function to convert a CIImage to CGImage in Swift.

func convertCIImageToCGImage(inputImage: CIImage) -> CGImage? {
    let context = CIContext(options: nil)
    if let cgImage = context.createCGImage(inputImage, from: inputImage.extent) {
        return cgImage
    }
    return nil
}

Notes:

• CIContext(options: nil) will use a software renderer and can be quite slow. To improve the performance, use CIContext(options: [CIContextOption.useSoftwareRenderer: false]) - this forces operations to run on GPU, and can be much faster.
• If you use CIContext more than once, cache it as apple recommends.

See the CIContext documentation for createCGImage:fromRect:

CGImageRef img = [myContext createCGImage:ciImage fromRect:[ciImage extent]];

From an answer to a similar question: https://stackoverflow.com/a/10472842/474896

Also since you have a CIImage to begin with, you could use CIFilter to actually crop your image.