im2bw help: image threshold array

Is there any way to get the output of im2bw to go into an array?

I know the function BW = im2bw(I, level) produces a black white image and that bwboundaries(bw) will then draw the boundarys

I want to do this a bunch for the same image when arrays don't seem to work? my code looks like this.

I=imread('matmap.bmp');

b=I(:,:,3);

for a=1:1:20

bw(a)=im2bw(b, a/20);

end

imshow(I)

hold on

for k = 1:numel(bw)

bb(k)=bwboundaries(bw);

plot(bb{k}(:,2), bb{k}(:,1), 'b', 'Linewidth', 1)

end

Answer 1

[Image Analyst]

Why are you doing two separate loops??? You need to put the call to bwboundaries() immediately after im2bw() - right there in the same loop.

[Morpheuskibbe]

you mean something like this?

for a=1:1:20

bb(a)=bwboundaries(im2bw(b, a/20));

end

still doesn't seem to like me using an array

[Image Analyst]

No. Here's a full demo:

% rgbImage = imread('peppers.png');
rgbImage = imread('onion.png');
% Extract blue channel.
b = im2double(rgbImage(:,:,3));
subplot(5,5, 1);
imshow(rgbImage)
subplot(5,5, 2);
imshow(b);
title('Blue Channel', 'FontSize', 13);
for a = 1 : 20
  bw = im2bw(b, a/20);
  subplot(5,5, a + 2);
  imshow(bw);
  caption = sprintf('a/20 = %.4f', a/20);
  title(caption, 'FontSize', 13);
  hold on;
  boundaries = bwboundaries(bw);
  for k = 1 : length(boundaries)
    plot(boundaries{k}(:,2), boundaries{k}(:,1), 'b', 'Linewidth', 1);
  end
  drawnow;
end

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')