p120fig03.43 Four paintings by Monet of the Rouen cathedral under different lighting conditions (top row) and their monochromatic versions (bottom row).  See the text for details.<BR>|| p119c2h0.25 "... Monet uses nearby colors that are nearly equiluminant, and sharp, high-contrast luminance defined edges are sparse.  He hereby creates weaker boundary signals within and between the parts of many forms, and stronger boundary signals between the forms. This combination facilitates color spreading within the forms and better separation of brightness and collor differences between forms. ... The grayscale versions of these paintings demonstrate the near equiluminance of the brushstrokes within forms, and places in which brightness and color differences significantly influence the groupings that differentiate between forms, including the differentiation between the cathedral and the sky.  ..."