Basics of MATLAB and Beyond

We define a red disc by setting all the pixels that are within a circle toone; all the other pixels are zero. The circle is defined by the equation:(x − x 0 ) 2 +(y − y 0 ) 2 = R 2 ,where (x 0 ,y 0 ) is the centre of the circle, and R is the radius. We set thecentre of the red disc to (−0.4, −0.4) and the radius to 1.0:R = 1.0;r = zeros(size(x));rind = find((x + 0.4).^2 + (y + 0.4).^2 < R^2);r(rind) = 1;The green and blue discs are defined in the same way, just shifting thecentre of the circle in each case:g = zeros(size(x));gind = find((x - 0.4).^2 + (y + 0.4).^2 < R^2);g(gind) = 1;b = zeros(size(x));bind = find(x.^2 + (y - 0.4).^2 < R^2);b(bind) = 1;Now we concatenate the matrices r, g, and b into one 200 × 200 × 3matrix called rgb:rgb = cat(3,r,g,b);We use rgb as an input to imagesc, which interprets the intensities inthe range 0.0 to 1.0:imagesc(rgb)axis equal offOn your screen you can see these as overlapped discs of coloured light.Exercise 13 Redefine the red, green, and blue discs so thatinstead of a circular disc of light at uniform maximum intensity,the intensity increases within each circle from zero at the centreto one at the edge; outside the circles the intensity should be zero.Create the new overlapped image. (Answer on page 189.)c○ 2000 by CRC Press LLC