code: public ColorImg getPhaseSpectrumImg(){
  		ColorImg phaseImg = new ColorImg(this.getDimension(), false);
  		// compute phase colors
  		phaseImg.forEach(px->{
  			double phase = this.computePhase(px.getIndex());
  			// get phase position on unit circle in a*b* plane
  			double x = Math.cos(phase);
  			double y = Math.sin(phase);
  			// set color (0.2 is ~max radius for which colors are still in RGB gammut at L*=0.74 )
  			px.setValue(1, 0.5+0.2*x);
  			px.setValue(2, 0.5+0.2*y);
  		});
  		// set luminance to 0.74 (greatest RGB range around center here)
  		phaseImg.fill(0, 0.74);
  		// convert from LAB 2 RGB
  		phaseImg.forEach(ColorSpaceTransformation.LAB_2_RGB);
  		return phaseImg;
  	}
docs: Returns a {@link ColorImg} showing the phase of this ComplexImg intended for display.
  The phase angle values are mapped to the a*b* plane of CIE L*a*b* so that same color
  indicates same angle.
  CIE L*a*b* is chosen to ensure a perceived constant luminance of the colors.
  
  @return phase spectrum image for display
  
  @see #getPowerSpectrumImg()
  @see #getPowerPhaseSpectrumImg()