detect square in image

i want to detect square shape only in image. how can i do this using matlab?

Answer 1

[Chandra Kurniawan]

Hello,

Is your goal only to detect square in this picture?

If so, you don't need to do shape recognition, etc.

You just need to perform some morphologichal operations only.

I = imread('3617ca70.png');
Ibw = ~im2bw(I,graythresh(I));

Ifill = imfill(Ibw,'holes');
Iarea = bwareaopen(Ifill,100);
Ifinal = bwlabel(Iarea);

stat = regionprops(Ifinal,'boundingbox');
imshow(I); hold on;
for cnt = 1 : numel(stat)
    bb = stat(cnt).BoundingBox;
    rectangle('position',bb,'edgecolor','r','linewidth',2);
end

And the result :

Is this what you need?

[Abdul]

yes, thanks a lot. how about detecting circle in image?

[An Hoang]

thank you so much! How to determine whether a check box option is selected

[N/A]

Can you please explain what do we get in stat variable ? It's something related to border line of each square, but i misunderstand what that means

Thanks

Answer 2

[Sean de Wolski]

Those squares are very well defined.

• Set a less than threshold to make the dark colors true and everything else false. ( BW = I<thresh )
• Perform a connected components analysis ( doc bwconncomp)
• Then regionprops with EulerNumber specified.
• Apply a threshold to the regions matching the EulerNumber ( idx = [stats(:).EulerNumber] == x ) of a sample square.
• Build a new matrix of false. ( BWnew = false(CC.ImageSize))
• Set the indices in the connected components analysis corresponding to the matching EulerNumber to true. ( BWnew(vertcat(CC.PixelIdxList{idx})) = true)

In theory you'll have a mask of the boxes.

Answer 3

[Naz]

I just thought of an alternative idea. Instead of detecting a square, you should register the image (filled form) of interest with the raw image. Then, since you know the coordinates of each square, you can just check the pixels at those coordinates for the white/black values.