(a) Because the infrared image which was used in place of the red component image has very high gray-level values.(b) The water appears as solid black (0) in the near infrared image [Fig. 6.27(d)].Threshold the image with a threshold value slightly larger than 0. The result is shown in Fig. P6.17. It is clear that coloring all the black points in the desired shade of blue presents no difficulties.(c) Note that the predominant color of natural terrain is in various shades of red.We already know how to take out the water from (b). Therefore, a method thatactually removes the “background” of red and black would leave predominantlythe other man-made structures, which appear mostly in a bluish light color. Re-moval of the red [and the black if you do not want to use the method as in (b)]can be done by using the technique discussed in Section 6.7.2.