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       al_color_distance_ciede2000_lab - Allegro 5 API


              #include <allegro5/allegro_color.h>


       This  function  computes the CIEDE2000 color difference between two RGB colors.  This is a
       visually uniform color difference, unlike for example the RGB distance.

       When using the RGB distance (Euklidean distance between two RGB  triplets)  there  can  be
       color  pairs  with the same distance, where the colors of one pair appear to be almost the
       same color, while the colors of the other pair look quite different.  This is improved  by
       using  the  L*a*b*  color  space  which  was  designed with perceptual uniformity in mind.
       However it  still  is  not  completely  uniform.   The  CIEDE2000  formula  contains  some
       additional transformations to fix that.

       The  returned  color distance is roughly in the range 0 (identical color) to 1 (completely
       different color) - but values greater than one are possible.

              Note: This function uses  al_color_lab(3alleg5)  internally  which  defines  the  L
              component to be in the range 0..1 (and not 0..100 as is sometimes seen).