code: public int getGrey(final int redWeight, final int greenWeight, final int blueWeight){
  		return Pixel.getGrey(getValue(), redWeight, greenWeight, blueWeight);
  	}
docs: Calculates the grey value of this pixel using specified weights.
  @param redWeight weight for red channel
  @param greenWeight weight for green channel
  @param blueWeight weight for blue channel
  @return grey value of pixel for specified weights
  @throws ArithmeticException divide by zero if the weights sum up to 0.
  @throws ArrayIndexOutOfBoundsException if this Pixel's index is not in
  range of the Img's data array.
  @see #getLuminance()
  @see #getGrey(int, int, int, int)
  @since 1.2