15.1 A handful of light-colored marbles is thrown down on a black tablecloth. Each marble has a diameter of 13 mm. An 8-bit digital photograph is taken of a 10 x 15 cm area of the tablecloth and marbles. A histogram for the image, which contains only eight distinct colors, is described in Table 15.5.

a. How many marbles appear in the photograph?

b. If the marbles are solid in color, how many different colors are there? How many marbles of each color appear in the image?

Table 15.5

Gray Scale Level	Number of Pixels
18	83
20	12171
21	1656
25	42
180	541
188	136
209	119
216	252