gistfile1.txt

import Foundation
import CoreImage
import UIKit

func convertCIImageToUIImage(ciImage: CIImage) -> UIImage {
    let context = CIContext(options: nil)
    let cgImage = context.createCGImage(ciImage, from: ciImage.extent)
    let uiImage = UIImage(cgImage: cgImage!)
    return uiImage
}

func convertUIImageToCIImage(uiImage: UIImage) -> CIImage {
    guard let ciImage = uiImage.ciImage ?? CIImage(image: uiImage) else {
        fatalError("Failed to convert UIImage to CIImage.")
    }
    return ciImage
}

func applyCustomCIFilter(uiImage: UIImage)-> UIImage? {
    let origImage = convertUIImageToCIImage(uiImage: uiImage)


    // custom filter to convert light gray to white and dark gray to black
    let invertWithThresholdKernel = CIColorKernel(source: """
        kernel vec4 invertWithThreshold(__sample pixel, float threshold) {
            // Determine the saturation by comparing the range of colors.
            // If the most intense channel is very close to the least intense channel,
            // then this color is close to gray.
            float minColor = min(pixel.r, min(pixel.g, pixel.b));
            float maxColor = max(pixel.r, max(pixel.g, pixel.b));

            float saturation = maxColor == 0.0 ? 0.0 : (maxColor - minColor) / maxColor;

            if (saturation < threshold) {
                // Invert the color, setting alpha to 1
                // Handling transparency requires first unmultiplying the colors. Rather than mess with that,
                // this code assumes that everything is opaque.
                return vec4(1.0 - pow(pixel.r, 2.2), 1.0 - pow(pixel.g, 2.2), 1.0 - pow(pixel.b, 2.2), 1.0);
            } else {
                return pixel;
            }
        }
    """)

    guard let outImage = invertWithThresholdKernel?.apply(extent: (origImage.extent), arguments: [origImage as Any, 0.1 as Float])! else { return nil }

    return convertCIImageToUIImage(ciImage: outImage);
}

I would be curious to know what's the correct way to use this in a widget since the CIColorKernel is deprecated but Metal shaders don't seem to be supported in widgets?