code: public static void diffAbs( GrayU8 imgA , GrayU8 imgB , GrayU8 output ) {
  		InputSanityCheck.checkSameShape(imgA,imgB);
  		output.reshape(imgA.width,imgA.height);
  
  		if( BoofConcurrency.USE_CONCURRENT ) {
  			ImplPixelMath_MT.diffAbs(imgA, imgB, output);
  		} else {
  			ImplPixelMath.diffAbs(imgA, imgB, output);
  		}
  	}
docs: <p>
  Computes the absolute value of the difference between each pixel in the two images.<br>
  d(x,y) = |img1(x,y) - img2(x,y)|
  </p>
  @param imgA Input image. Not modified.
  @param imgB Input image. Not modified.
  @param output Absolute value of difference image. Can be either input. Modified.