imageToBlackOnWhite function

Future<Image> imageToBlackOnWhite(Image inputImage, { int backgroundBrightNestthreshold_0_255 = 190, })

Binarize an input image by converting it to black and white based on a brightness threshold.

This function takes an input ui.Image and converts it to a black and white image where pixels brighter than the specified backgroundBrightNestthreshold_0_255 become white, and those below become black.

Parameters:

• inputImage: The source image to be binarized.
• backgroundBrightNestthreshold_0_255: Optional. The brightness threshold used to determine black or white pixels. Defaults to 190. Range is 0-255.

Returns: A Future that resolves to a new ui.Image containing the binarized version of the input image.

Throws: An Exception if it fails to get image data from the input image.

Implementation

Future<ui.Image> imageToBlackOnWhite(
  final ui.Image inputImage, {
  final int backgroundBrightNestthreshold_0_255 = 190,
}) async {
  final int width = inputImage.width;
  final int height = inputImage.height;
  final Uint8List pixels = await imageToUint8List(inputImage);

  // Create a new Uint8List for the output image
  final Uint8List outputPixels = Uint8List(width * height * 4);

  for (int i = 0; i < pixels.length; i += 4) {
    final int r = pixels[i];
    final int g = pixels[i + 1];
    final int b = pixels[i + 2];
    // ignore: unused_local_variable
    final int a = pixels[i + 3];

    // Calculate brightness using a weighted average
    final double brightness = (0.299 * r + 0.587 * g + 0.114 * b);

    // If brightness is above the threshold, set pixel to white, otherwise black
    if (brightness > backgroundBrightNestthreshold_0_255) {
      // make this the background paper
      outputPixels[i] = 255; // R
      outputPixels[i + 1] = 255; // G
      outputPixels[i + 2] = 255; // B
    } else {
      // make this the foreground ink
      outputPixels[i] = 0; // R
      outputPixels[i + 1] = 0; // G
      outputPixels[i + 2] = 0; // B
    }

    // remove alpha
    outputPixels[i + 3] = 255; // A
  }

  return await createImageFromPixels(outputPixels, width, height);
}