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distance between edges in video processing.

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i have to find the distance between edges. attached images of micro-gripper. smaller arm will deflect when voltage is supplied . i have to monitor gap between arms continuously for designing control algorithm. i'm using video processing (webcam).

Accepted Answer

Image Analyst
Image Analyst on 9 Dec 2015
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 long g;
format compact;
fontSize = 20;
% Read in a gray scale demo image.
folder = pwd;
baseFileName = 'microgripper_grayscale.jpg';
% Get the full filename, with path prepended.
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.
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);
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
% It's not really gray scale like we expected - it's color.
% Convert it to gray scale by taking only the green channel.
grayImage = grayImage(:, :, 2); % Take green channel.
% Display the image.
subplot(2, 2, 1);
imshow(grayImage, []);
axis on;
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Crop the image
grayImage = grayImage(1:160,50:250);
% Display the image.
subplot(2, 2, 2);
imshow(grayImage, []);
axis on;
title('Cropped Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
% 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')
% Let's compute and display the histogram.
[pixelCount, grayLevels] = imhist(grayImage);
subplot(2, 2, 3);
bar(grayLevels, pixelCount); % Plot it as a bar chart.
grid on;
title('Histogram of original image', 'FontSize', fontSize, 'Interpreter', 'None');
xlabel('Gray Level', 'FontSize', fontSize);
ylabel('Pixel Count', 'FontSize', fontSize);
xlim([0 grayLevels(end)]); % Scale x axis manually.
% Get the average vertical profile
horizontalProfile = mean(grayImage, 1);
% Plot the profile
subplot(2, 2, 4);
plot(horizontalProfile, 'LineWidth', 2);
grid on;
title('Average Horizontal Profile', 'FontSize', fontSize, 'Interpreter', 'None');
% Get the width of all the bright regions.
% First we need to binarize the profile.
binaryImage = horizontalProfile > 100;
% Label the regions.
labeledRegions = bwlabel(binaryImage);
% Make the area measurements, which is really the length of the region.
measurements = regionprops(labeledRegions, 'Area');
% Get the width of the second region, which is the intergripper gap.
gripperGap = measurements(2).Area;
% Tell user
message = sprintf('The average gap between the gripper fingers is %.3f pixels', gripperGap);

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