MATLAB - Colour an Area around a bounding box with Black - matlab

Question

I have a code that detects a face in an image and places a bounding box around the image like below.
But I want to go further and colour the area outside the bounding box black so that only the face can be seen and the background becomes black.
Original code..
FDetect = vision.CascadeObjectDetector;
I = imread('PresidentClinton.jpg');
%Returns Bounding Box values based on number of objects
BB = step(FDetect,I);
figure,
imshow(I); hold on
for i = 1:size(BB,1)
rectangle('Position',BB(i,:),'LineWidth',5,'LineStyle','-','EdgeColor','r');
end
title('Face Detection');
hold off;

Answer 1

Here is a simple method in which you first create a target image of the same size/class as your original image and fill it with black. Then you get the rectangle coordinates and assign the data from the original image to the target image:
clear
close all
A = imread('peppers.png');
B = zeros(size(A),class(A)); % //Pre-define target image of identical size and class than original.
%// You could also use this line:
%//B = zeros(size(A),'like',A);
hRect = rectangle('Position',[100 100 200 160],'LineWidth',3); %// Define rectangle
RectPos = get(hRect, 'Position'); %// Get the coordinates of the rectangle.
x = RectPos(1):RectPos(1)+RectPos(3); %// Define x- and y-span
y = RectPos(2):RectPos(2)+RectPos(4);
B(x,y,:) = A(x,y,:); %// Assign the selected part of the image to B
figure
subplot(1,2,1)
imshow(A)
subplot(1,2,2)
imshow(B)
Giving something like this:
There are other ways of course but I think this one is straightforward and easy to implement in a loop.