MATLAB: How to calculate area region growing

Question

Hi all, i use function region growing. my script as below. it work. but how to know the area of the growing?

i used regionprops but error pop up. anyone can help me?

note: the pixel value for my region is 1, and the rest is 0. i want to know the total area of 1 (in red circle).

clc
clear all
A = im2double(imread('medtest.png'));
figure, imshow(A);
J = regiongrowing(A);
figure, 
B = imshow(A+J);
T = regionprops('table', B,'Area','Centroid')

ERROR!!!!

Error using regionprops
Expected input number 2, L, to be one of these types:
uint8, uint16, uint32, int8, int16, int32, single, double, categorical
Instead its type was matlab.graphics.primitive.Image.
Error in regionprops (line 235)
    validateattributes(L, supportedTypes, supportedAttributes, ...
Error in rg (line 8)
T = regionprops('table', B,'Area','Centroid')

Answer 1

B =A+J;