compute method

@override double compute(Image image)

Implementation

@override
double compute(img.Image image) {
  final width = image.width;
  final height = image.height;
  final data = Float64List(width * height);

  for (int y = 0; y < height; y++) {
    for (int x = 0; x < width; x++) {
      data[y * width + x] = pixelToGray(image, x, y);
    }
  }

  List<double> haarTransform(List<double> data, int size) {
    if (size == 1) return data;

    final halfSize = size ~/ 2;
    final result = List<double>.generate(size, (i) => 0.0);

    for (int i = 0; i < halfSize; i++) {
      result[i] = (data[2 * i] + data[2 * i + 1]) / sqrt(2);
      result[halfSize + i] = (data[2 * i] - data[2 * i + 1]) / sqrt(2);
    }

    final transformed = haarTransform(result.sublist(0, halfSize), halfSize);
    transformed.addAll(result.sublist(halfSize, size));
    return transformed;
  }

  final result = haarTransform(data.toList(), width * height);
  double sum = 0;

  for (double value in result) {
    sum += value * value;
  }

  return sqrt(sum) / (width * height);
}