如何使用Matlab检测局部矩形并对齐图像？

Question

I was wondering how it would be possible to detect the bottom right corner of a paper square I manually made (which is probably not perfectly a square, because I drew it myself) on top of another object. What I want to do is use this square as a reference and align the image according to the bottom right corner of the square. I'm quite a Matlab amateur. Can anybody help?

The top left square is the paper square I need to detect which is the reference point.

Answer 1

You have a lot of choices to detect the square; it's actually a rectangle; you want to detect, but the easiest way is using morphological operations. Here I provided a commented script to help you; since you are a MATLAB amateur.

ShowMaskAsOverlay is not a built-in command in MATLAB, though, It is very useful. If you want to download it visit this link .

Another way I would suggest from what I understood from your question. You can save the image before making the square, and save another image after making the square. Then you will only need to get the difference between the two images.

close all;clear all;clc;

% Read in Image
im = imread('stack.png');

[r, c, ch] = size(im);

% Convert Image to Gray if it's RGB
if ch == 3
    gray = rgb2gray(im);
end

% Threshold Value; > 0.87 = 1 and  < 0.87 = 0
thresh = 0.87;
bw = im2bw(gray, thresh);

% Removing unwanted white pixels
bw = bwareaopen(bw, 400);
bw = imerode(bw, strel('disk', 3));
bw = imfill(bw, 'holes');
bw = bwareaopen(bw, 600);
bw = imdilate(bw, strel('disk', 3)); %optional. Could be omitted

% Calculating the BoundingBox of the Square
s = regionprops(bw, 'BoundingBox');
box = struct2cell(s);
pos = cell2mat(box);

%% Displaying Images
figure(1)
imshow(im)
rectangle('position', pos, 'edgecolor', 'red', 'linewidth', 1.5)
str = ['Bounding Box Bottom Right Corner Coordinate Value = ', num2str(pos(4))];
h = text(pos(3), pos(4), num2str(pos(4)));
set(h, 'Color', 'k', 'FontSize', 12, 'FontWeight', 'bold')
title(str)

figure(2)
imshow(gray)
showMaskAsOverlay(0.5, bw, 'g')