Alternatively you could just sum the binary image horizontally and vertically, or use any(), and look for where it's first land last non-zero. Here's the demo for that method:
% Demo to find the bounding box of coins with any() and crop out the subimage.
clc; % Clear the command window.
workspace; % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;
% Check that user has the Image Processing Toolbox installed.
hasIPT = license('test', 'image_toolbox');
if ~hasIPT
% User does not have the toolbox installed.
message = sprintf('Sorry, but you do not seem to have the Image Processing Toolbox.\nDo you want to try to continue anyway?');
reply = questdlg(message, 'Toolbox missing', 'Yes', 'No', 'Yes');
if strcmpi(reply, 'No')
% User said No, so exit.
return;
end
end
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
% Get the full filename, with path prepended.
baseFileName = 'eight.tif';
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
% File doesn't exist -- didn't find it there. Check the search path for it.
fullFileName = baseFileName; % No path this time.
if ~exist(fullFileName, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
uiwait(warndlg(errorMessage));
return;
end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(grayImage);
% Display the original gray scale image.
subplot(2, 3, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off')
% Let's compute and display the histogram.
[pixelCount, grayLevels] = imhist(grayImage);
subplot(2, 3, 2);
bar(pixelCount);
grid on;
title('Histogram of original image', 'FontSize', fontSize);
xlim([0 grayLevels(end)]); % Scale x axis manually.
% Threshold the image to get a binary image.
binaryImage = grayImage < 175;
% Display the image.
subplot(2, 3, 3);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize);
% Get vertical profile.
verticalProfile = any(binaryImage, 2);
subplot(2, 3, 4);
plot(verticalProfile, 'b-', 'LineWidth', 4);
grid on;
title('Vertical Profile', 'FontSize', fontSize);
xlabel('Row', 'FontSize', fontSize);
% Get Horizontal profile.
horizontalProfile = any(binaryImage, 1);
subplot(2, 3, 5);
plot(horizontalProfile, 'b-', 'LineWidth', 4);
grid on;
title('Horizontal Profile', 'FontSize', fontSize);
xlabel('Column', 'FontSize', fontSize);
% Find what index the bounding box is at
topRow = find(verticalProfile, 1, 'first')
bottomRow = find(verticalProfile, 1, 'last')
leftCol = find(horizontalProfile, 1, 'first')
rightCol = find(horizontalProfile, 1, 'last')
% Plot box around original
xBox = [leftCol, rightCol, rightCol, leftCol, leftCol]
yBox = [topRow, topRow, bottomRow, bottomRow, topRow]
subplot(2, 3, 1);
hold on;
plot(xBox, yBox, 'r', 'LineWidth', 2);
% Crop it out of the original:
croppedImage = grayImage(topRow:bottomRow, leftCol:rightCol);
% Display the image.
subplot(2, 3, 6);
imshow(croppedImage, []);
title('Cropped Image', 'FontSize', fontSize);
