Matlab crop a polygon from an image - matlab

Question

I have an image of a product on a solid background that I would like to crop as close as possible to the product.
I brighten it and find the edges with the following code:
limits = stretchlim(original, 0.01);
img1 = imadjust(original, limits, []);
img = rgb2gray(img1);
BW = edge(img,'canny',0.2);
[B,L,N,A] = bwboundaries(BW);
figure; imshow(BW); hold on;
for k=1:length(B),
if(~sum(A(k,:)))
boundary = B{k};
plot(boundary(:,2),boundary(:,1),'r','LineWidth',2);hold on;
end
end
Which give me the following image:
The following code gives me rectangles on every blob/line detected:
blobMeasurements = regionprops(logical(BW), 'BoundingBox');
numberOfBlobs = size(blobMeasurements, 1);
rectCollection = [];
for k = 1 : numberOfBlobs % Loop through all blobs.
rects = blobMeasurements(k).BoundingBox; % Get list ofpixels in current blob.
x1 = rects(1);
y1 = rects(2);
x2 = x1 + rects(3);
y2 = y1 + rects(4);
x = [x1 x2 x2 x1 x1];
y = [y1 y1 y2 y2 y1];
rectCollection(k,:,:,:) = [x1; y1; x2; y2];
end
I'm able to then draw a bounding rectangle and crop with all these points collected with the following code:
% get min max
xmin=min(rectCollection(:,1))-1;
ymin=min(rectCollection(:,2))-1;
xmax=max(rectCollection(:,3))+1;
ymax=max(rectCollection(:,4))+1;
% define outer rect:
outer_rect=[xmin ymin xmax-xmin ymax-ymin];
crop = imcrop(original,outer_rect);
Which gives me the following result:
My question is how can I get a polygon as close as possible to the product and crop it with the polygon or, alternatively, just crop as close as possible to the product and its cap?

Answer 1

If you don't want to get a bounding box but a polygon, I think you need to generate a mask - a matrix with the same size of your image, value 1 if the pixel in on your object, 0 if not.
I heard about an algorithm (sorry I can't find the name, I'll edit this post if I find it) which works with a lasso :
step 0 : your lasso is your bounding box.
step i : segment the lasso and for each part, you retract it if the color (or any other) gradient in the image is less than a fixed value.
step n (last) : you cannot retract any part of the lasso, it is finished. Inside your lasso : your object. Outside : the background.
As I remember there is a lot of work with this method : the definition of the lasso, the retractation step, the solidity of your lasso (to avoid too much deformation of the lasso).
Beside the lasso method you can search about the watershed transform, it can also work with your problem.
Finally, if you generate the pictures, take shots with a plained background (green, pink, blue, etc) and use a simple chromakey.

Answer 2

Using active contours also looks like a good approach but getting a nice mask is troublesome.
original = imread('1.jpg');
level = graythresh(original);
img = rgb2gray(original);
mask = im2bw(img,level+0.1);
mask = imfill(~mask,'holes');
bw = activecontour(img,mask);
rows = numel(original(:,1,1));
columns = numel(original(1,:,1));
for i = 1:rows
for j = 1:columns
if ( bw(i,j,1) == 0 )
original(i,j,:) = 255;
end
end
end
imshow(original);