my output value is double not logical

clear all;
clc;
img = imread('green2.jpg');
img_gray = rgb2gray(img);
level = graythresh(img);
img_bw = im2bw(img_gray,level);
imshow(img_bw);
[L2,num2]=bwlabel(img_bw,8); %連通區域標記
B2=false(size(L2));
for i=1:num2
    [r,c] = find(L2==i);
    left  = min(c);
    right = max(c);
    up    = min(r);
    down  = max(r);
    d     = (down-up) / (right-left);
    if d > 0.8 & d < 1
        % [x,y]=find(L2==i);  % Done above already
        B2 = B2 + bwselect(img_bw, c, r, 8); %%%把滿足長寬比在0.8到2的區域留下
    end
end
figure,imshow(B2);

why my B2 set logical but output is double value?

[Stephen23]

>> class(true+true)
ans = double

Answer 1

[KSSV]

A = logical(round(rand(2))) ;  % a logical class
B = rand(2) ;  % a double class
C = A+B   ;   % operation between logical and double gives double

So in your case B2 is logical and the output from bwselect(img_bw, c, r, 8) is double....so the result is double.

Have a look on logical and double if you want any conversions.