How to remove specified part in image and count number of objects in the image

There are more general ways to erase anything outside of the circle, but you don't need that if all you want to do is erase the micron bar and it's in the same location for all your images -- you can simply set that portion to zero like I did above.

However if you want to see the more general way, even though you don't need it, let me know. It probably involves imclose, imclearborder, and bwareafilt

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Image Analyst on 30 Dec 2022

Edited: Image Analyst on 30 Dec 2022

Open in MATLAB Online

objects in circle.png

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 = 18;
fileName = 'Objects in circle.png'
grayImage = imread(fileName);
[rows, columns, numberOfColorChannels] = size(grayImage)
if numberOfColorChannels > 1
	grayImage = grayImage(:, :, 1); % Take red channel only.
end
subplot(2, 2, 1);
imshow(grayImage)
axis on
impixelinfo
title('Original Image', 'FontSize', fontSize);
% Get a mask of white blobs.
mask = grayImage > 0;
% Get rid of white frame around his screenshot image.
mask = imclearborder(mask);
% Fill holes
se = strel('disk', 10, 8);
mask2 = imclose(mask, se);
mask2 = imfill(mask2, 'holes');
% Take largest and invert it.
mask2 = ~bwareafilt(mask2, 1);
% Display image.
subplot(2, 2, 2);
imshow(mask2)
axis on
impixelinfo
title('Mask Image', 'FontSize', fontSize);
% Use mask to erase pixels.
grayImage(mask2) = 0;
% Display image.
subplot(2, 2, 3);
imshow(grayImage)
axis on
impixelinfo
title('Masked Image', 'FontSize', fontSize);
% Count number of particles in mask
mask(mask2) = false;
% Label each blob with 8-connectivity, so we can make measurements of it
[labeledImage, numberOfBlobs] = bwlabel(mask, 4);
% Apply a variety of pseudo-colors to the regions.
coloredLabelsImage = label2rgb (labeledImage, 'hsv', 'k', 'shuffle');
% Display the pseudo-colored image.
subplot(2, 2, 4);
imshow(mask);
imshow(coloredLabelsImage);
% Get all the blob properties.  Can only pass in originalImage in version R2008a and later.
props = regionprops(labeledImage, 'Area');
numberOfBlobs = numel(props)
caption = sprintf('%d particles', numberOfBlobs)
title(caption, 'FontSize', fontSize);