Find Black Squares in Image ( matlab )

Question

i have hundreds of paper-forms and i want to automatically read this forms. The first step would be to calibrate the scanned paper. ( find the coordinates of the 4 squares )

But i don't know how to do it in matlab :(

here is the picture :

What have you tried to do or do you have an idea how you would do this in ? — Egon, Jul 29 '12 at 11:08

score 2 · Accepted Answer · edited May 23 '17 at 11:53

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Here is a solution using OpenCV. For detecting the paper sheet itself, see this.

edited May 23 '17 at 11:53

Community

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answered Jul 29 '12 at 11:57

Håvard Geithus

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score 1 · Answer 2 · answered Jul 29 '12 at 14:01

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Thanks Havard,

this solution helped me. This is what i did :

I = imread('inv-small.png');
BW = edge(I,'canny',0.3);
imshow(BW);
C = corner(BW,4);
imshow(I);
hold on
plot(C(:,1), C(:,2), 'r*');
hold off

results in : enter image description here

answered Jul 29 '12 at 14:01

fragant1996

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Did you try it when the inner part of the document is not blurred? – Håvard Geithus Jul 29 '12 at 15:42
If the input image has colors in it, you could e.g. do this: BW = im2bw(I,level), where level is some threshold like Otsu's: level = graythresh(I); – Håvard Geithus Jul 29 '12 at 15:45

Find Black Squares in Image ( matlab )

2 Answers2