code: public Pixel setRGB_fromDouble_preserveAlpha(double r, double g, double b){
  		return setValue((getValue() & 0xff000000) | (0x00ffffff & Pixel.rgb_fromNormalized(r, g, b)));
  	}
docs: Sets an RGB value at the position currently referenced by this Pixel.
  The present alpha value will not be altered by this operation. <br>
  Each channel value is assumed to be within [0.0 .. 1.0]. Channel values
  outside these bounds will be clamped to them.
  @param r normalized red
  @param g normalized green
  @param b normalized blue
  @throws ArrayIndexOutOfBoundsException if this Pixel's index is not in
  range of the Img's data array.
  
  @see #setRGB_preserveAlpha(int, int, int)
  @since 1.2