How can I solve this - Undefined operator '.^' for input arguments of type 'struct'. ?

clc;
close all;
clear all;

      Im = imread('B1_16.tif');
      I=rgb2gray(Im);
      I=adapthisteq(I);
      [row col]=size(I)
      double(I);
      figure
      imshow(I)

       % DoG filter (to improve the edge)
      sigma = 4;
  gauss1 = fspecial('gaussian', round([10*sigma 10*sigma]), sigma);
  sigma = 0.1;
  gauss2 = fspecial('gaussian', round([10*sigma 10*sigma]), sigma);
  blur1 = imfilter(I, gauss1, 'replicate', 'same');
  blur2 = imfilter(I, gauss2, 'replicate', 'same');
  dog = blur1 - blur2;
  figure
  imshow(dog)

      str = 'Click to select initial contour location. Double-click to confirm and proceed.';
      title(str,'Color','b','FontSize',12);
      disp(sprintf('\nNote: Click close to object boundaries for more accurate result.'));

      % Select region interactively
      mask = roipoly;

      figure, imshow(mask)
      title('Initial MASK');

      % Segment the image using active contours
      maxIterations = 1; % More iterations may be needed to get accurate segmentation. 
      bw = activecontour(I, mask, maxIterations, 'Chan-Vese');

      % Display segmented image
      figure, imshow(bw)
      title('Segmented Image');

      % find the features of the segmented area using function
      g=regionprops(bw,'all')
      % finding the area of the white area segmented from the previous images
      % area is the number of white pixel in the image

      numofpixels=sum(bw(:))% correct (num of pixels indicates the area of the segmented image)
      % numofpixels1=sum(I(:)) just to confirm that the algorithm used is
      % correct

      % measure the perimeter
      Perimeter=regionprops(bw,'perimeter')

      % determine the circularities 
      Circularities=Perimeter.^2/(4*pi*numofpixels)

      %perimeter
      pm=bwperim(bw,8)

      red=Im(:,:,1);
      green=Im(:,:,2);
      blue=Im(:,:,3);

      red(pm)=255;
      green(pm)=255;
      blue(pm)=0;
      out=cat(3,red,green,blue);

      figure 
      imshow(pm)

      figure 
      imshow(out)

Answer 1

[Walter Roberson]

Change

Perimeter=regionprops(bw,'perimeter')

to

rinfo = regionprops(bw,'perimeter');
Perimeter = [rinfo.Perimeter];

[matlab noob]

Hi Walter Roberson! thank you so much in solving my problem. But can you explain to me how [rinfo.Perimeter] work? sorry to ask such noob question.

[Walter Roberson]

regionprops will return a structure array with one element for each region found. You asked for perimeter so there will be one field, rinfo(1).Perimeter, rinfo(2).Perimeter and so on existing

When you name a structure array and a field, rinfo.Perimeter, then MATLAB converts that into a comma separated list, as if you had written rinfo(1).Perimeter, rinfo(2).Perimeter and so on at that point. With [] there, that becomes

Perimeter = [rinfo(1).Perimeter, rinfo(2).Perimeter, ....]

which is the horizontal concatenation of the Perimeter values for all of the elements. The effect is the same as

for K = 1 : length(rinfo)
  Perimeter(K) = rinfo(K).Perimeter;
end

since all of the items are scalar.

[matlab noob]

Thank you so much!