distance method

@override double distance(List<double> one, List<double> two)

Standard CIE 1976 delta E formula also takes the square root, unneeded here. This method is used by quantization algorithms to compare distance, and the relative ordering is the same, with or without a square root.

This relatively minor optimization is helpful because this method is called at least once for each pixel in an image.

Implementation

@override
double distance(List<double> one, List<double> two) {
  final dL = one[0] - two[0];
  final dA = one[1] - two[1];
  final dB = one[2] - two[2];
  return dL * dL + dA * dA + dB * dB;
}