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detect checkerboard pattern (non-solid dark colour)

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zepp
zepp on 30 Mar 2017
Answered: Image Analyst on 31 Mar 2017
I am trying to detect the checkerboard points in the image below. If that's not possible, I would like to split the image into 64 different blocks, one for each square.
Now, detectCheckerboardPoints won't work here because of the dashed lines. Is there an easy way to do this?
Thanks

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Accepted Answer

Image Analyst
Image Analyst on 31 Mar 2017
OK, try this code:
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
clear; % Erase all existing variables. Or clearvars if you want.
workspace; % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 15;
%===============================================================================
% Get the name of the image the user wants to use.
baseFileName = '1.png'; % Assign the one on the button that they clicked on.
% Get the full filename, with path prepended.
folder = []; % Determine where demo folder is (works with all versions).
fullFileName = fullfile(folder, baseFileName);
%===============================================================================
% Read in a demo image.
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
% It's not really gray scale like we expected - it's color.
% Use weighted sum of ALL channels to create a gray scale image.
grayImage = rgb2gray(grayImage);
% ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
% which in a typical snapshot will be the least noisy channel.
% grayImage = grayImage(:, :, 2); % Take green channel.
end
% Display the image.
figure;
imshow(grayImage, []);
axis on;
caption = sprintf('Original Gray Scale Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo();
% 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')
hold on;
drawnow;
checkerBoardRows = round(linspace(14, 1268, 9));
checkerBoardColumns = round(linspace(11, 1257, 9));
for row = 1 : length(checkerBoardRows)
thisRow = checkerBoardRows(row);
line([thisRow, thisRow], [checkerBoardRows(1), checkerBoardRows(end)],...
'Color', 'r', 'LineWidth', 2);
end
for col = 1 : length(checkerBoardColumns)
thisCol = checkerBoardColumns(col);
line([checkerBoardColumns(1), checkerBoardColumns(end)], [thisCol, thisCol],...
'Color', 'r', 'LineWidth', 2);
end
figure;
plotNumber = 1;
% Now crop out 64 chunks.
for row = 1 : length(checkerBoardRows)-1
row1 = checkerBoardRows(row);
row2 = checkerBoardRows(row+1) - 1;
for col = 1 : length(checkerBoardColumns)-1
col1 = checkerBoardColumns(col);
col2 = checkerBoardColumns(col+1) - 1;
subplot(8, 8, plotNumber);
subImage = grayImage(row1:row2, col1:col2);
imshow(subImage);
drawnow;
if plotNumber == 1
% 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')
hold on;
drawnow;
end
plotNumber = plotNumber + 1;
end
end

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More Answers (1)

Image Analyst
Image Analyst on 30 Mar 2017
Edited: Image Analyst on 31 Mar 2017
The image is well aligned. Just do this:
axis on;
So you can see what elements each square starts and stops on. Then make up a 1-D array of rows and columns that divide each square.
rows = [1, 100, ..... whatever
columns = [1, 100, ..... whatever
To see all 64, just extract and show
for k = 1 : length(rows)
r1 = rows(k);
r2 = rows(k+1)-1;
%etc........
end

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