This overlay compares the relative depths of Back (I) and Back (II) up to a difference of 5 centimeters, precisely visualizing the two directions of his work. Areas of blue and purple record where Back (II) is 3 to 5 centimeters higher (where Matisse added new plaster to the surface of the Back [I] cast); areas of yellow and orange identify features that are 2 to 3 centimeters lower (where he carved away the surface). Gray areas indicate more than 5 cm of difference.