code: func (i InterpolationFunction) kernel() (int, func(float64) float64) {
  	switch i {
  	case Bilinear:
  		return 2, linear
  	case Bicubic:
  		return 4, cubic
  	case MitchellNetravali:
  		return 4, mitchellnetravali
  	case Lanczos2:
  		return 4, lanczos2
  	case Lanczos3:
  		return 6, lanczos3
  	default:
  		// Default to NearestNeighbor.
  		return 2, nearest
  	}
  }
docs: // kernal, returns an InterpolationFunctions taps and kernel.