[Octave-bug-tracker] [bug #44100] image package: regionprops could easily deliver more properties

[H. G.]

Follow-up Comment #4, bug #44100 (project octave):

Sorry for the confusion. Here is a shorter version that does the very same: 


   case "majoraxislength"
        for k = 1:num_labels
          [Y, X] = find (L == k);
          if (numel(Y) > 1)
            % calculate (centralised) second moment of region
            C = cov ([X(:), Y(:)]);
            lambda = eig (C);
            retval (k).MajorAxisLength = 4 * sqrt(max(lambda));            
          else
            retval (k).MajorAxisLength = 1;
          endif
        endfor 

     case "minoraxislength" 
        for k = 1:num_labels
          [Y, X] = find (L == k);
          if (numel(Y) > 1)
            % calculate (centralised) second moment of region
            C = cov ([X(:), Y(:)]);
            lambda = eig (C);            
            retval (k).MinorAxisLength = 4 * sqrt(min(lambda));
          else
            retval (k).MinorAxisLength = 1;
          endif
        endfor    

    case "eccentricity" 
        for k = 1:num_labels
          [Y, X] = find (L == k);
          if (numel(Y) > 1)
            % calculate (centralised) second moment of region
            C = cov ([X(:), Y(:)]);
            lambda = eig (C);
            major =  2 * sqrt(max(lambda));
            minor =  2 * sqrt(min(lambda));
            retval (k).Eccentricity = sqrt((major)^2 - (minor)^2) / major; 
          else
            retval (k).Eccentricity = 0; % a circle has 0 eccentricity
          endif
        endfor 


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