MATLAB: Measure object width in a depth image (able to choose shoulder width in the image)

Question

How to measure shoulder width of a depth image? I am advice to use these equation so that i will manage to get a shoulder width

Xi,j = ( j – W/2 ) x 320/W x M x Zi,j

Yi,j– = ( j – W/2 ) x 240/h x M x Zi,j

(attached are my depth image) 1st picture is the original image 2nd picture i convert original image from mat2gray. Your advice is greatly appreciate.

Answer 1

Try this:

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 short g;
format compact;
fontSize = 25;
%===============================================================================

% Get the name of the image the user wants to use.
baseFileName = 'depth6.png';
% Get the full filename, with path prepended.
folder = pwd
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
  % The file doesn't exist -- didn't find it there in that folder.
  % Check the entire search path (other folders) for the file by stripping off the folder.
  fullFileNameOnSearchPath = baseFileName; % No path this time.
  if ~exist(fullFileNameOnSearchPath, '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
%===============================================================================
% Read in 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 original image.
subplot(2, 2, 1);
imshow(grayImage, []);
axis on;
caption = sprintf('Original Image, %s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% 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')
% Find the white surround.
binaryImage = grayImage > 45000 & grayImage < 50000;
% Fill the image to get rid of black spot at center.
binaryImage = imfill(binaryImage, 'holes');
% Take the largest blob only.
binaryImage = bwareafilt(binaryImage, 1);
% Display the image.

subplot(2, 2, 2);
histogram(grayImage);
title('Histogram of depth image', 'FontSize', fontSize);
grid on;
subplot(2, 2, 3);
imshow(binaryImage, []);
axis on;
caption = sprintf('Binary Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;
% Get the bounding box of the blob.
props = regionprops(binaryImage, 'BoundingBox');
yTop = props.BoundingBox(2)
xLeft =  props.BoundingBox(1)
width =  props.BoundingBox(3);
height =  props.BoundingBox(4);
% Erase bottom half, assuming shoulders won't be down there.
yBottom = round(yTop + height/2);
binaryImage(yBottom:end, :) = false;
% Display the image.
subplot(2, 2, 4);
imshow(binaryImage, []);
axis on;
caption = sprintf('Binary Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
% Get bounding box again on just the top half
props = regionprops(binaryImage, 'BoundingBox');
boundingBox = props.BoundingBox
yTop = boundingBox(2)
xLeft =  boundingBox(1)
shoulderWidth =  boundingBox(3)
height =  boundingBox(4)
% Put up red rectangle around shoulders:
rectangle('Position', round(boundingBox), 'EdgeColor', 'r', 'LineWidth', 2);
message = sprintf('The shoulder width = %d', shoulderWidth);
title(message, 'FontSize', fontSize, 'Interpreter', 'None');
uiwait(helpdlg(message));