MATLAB: Image segmentation – Specify an area of interest

circleImage Processing Toolboxposition;size;

Hi guys,
I have two images ('A' and 'B'). On the first image 'A' there are circle-shaped objects e.g. those chips. What I did so far is to identify those objects with their information about coordinates and radii. Here is the toy-code for the first part:
rgb = imread('coloredChips.png');
figure
imshow(rgb)
d = imdistline;
delete(d);
gray_image = rgb2gray(rgb);
imshow(gray_image);
[centers, radii] = imfindcircles(rgb,[20 25],'ObjectPolarity','dark')
[centers, radii] = imfindcircles(rgb,[20 25],'ObjectPolarity','dark', ...
    'Sensitivity',0.9)
imshow(rgb);
h = viscircles(centers,radii);
Based on the information about the position and radii in 'A', I want to run a second edge detection algorithm on image 'B' to identify there a circle-shaped object, that lies somewhere within the object of the first picture 'A'. Both images has the same dimension.
Objective: Get the coordinates and radii of the objects in image 'A' and the same for image 'B'.
My thoughts: My idea was to draw rectangles around the main object in 'image' B and make the background black. This is not the best solution but it would reduce the running time.
Do you have any hints for me, how to solve this problem?
Thanks a lot.

Best Answer

You can use a mask of the circles, determined from A, on B and analyze what is remaining.
% Creates a mask from one image and applies it to an image.
clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
clearvars;
close all;
format long g;
format compact;
fontSize = 20;
rgbImage = imread('coloredChips.png');
% Get the dimensions of the image.  numberOfColorBands should be = 3.
[rows, columns, numberOfColorChannels] = size(rgbImage);
subplot(3, 2, 1);
imshow(rgbImage)
title('Original RGB Image', 'fontSize', fontSize);
% 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')
% d = imdistline;
% delete(d);
grayImage = rgb2gray(rgbImage);
subplot(3, 2, 2);
imshow(grayImage);
drawnow;
title('Gray Scale Image', 'fontSize', fontSize);
% [centers, radii] = imfindcircles(rgbImage,[20 25],'ObjectPolarity','dark')
[centers, radii] = imfindcircles(rgbImage,[20 25],'ObjectPolarity','dark', ...
  'Sensitivity',0.9)
subplot(3, 2, 3);
imshow(rgbImage);
h = viscircles(centers, radii);
title('Original RGB Image with Circles in Overlay', 'fontSize', fontSize);
% Make a binary image mask
subplot(3, 2, 4);
mask = false(rows, columns);
for k = 1 : length(centers)
  % Create a logical image of a circle with specified
  % diameter, center, and image size.
  % First create the image.
  [columnsInImage rowsInImage] = meshgrid(1:columns, 1:rows);
  % Next create the circle in the image.
  centerX = centers(k, 1);
  centerY = centers(k, 2);
  radius = radii(k);
  circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
  % circlePixels is a 2D "logical" array.
  % Now, display it.
  imshow(circlePixels) ;
  mask(circlePixels) = true;
  imshow(mask);
  drawnow;
end
imshow(mask);
title('Binary image mask', 'fontSize', fontSize);
% Mask the image using bsxfun() function
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));
subplot(3, 2, 5);
imshow(maskedRgbImage);
title('Masked RGB Image', 'fontSize', fontSize);
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