Done http://hg.code.sf.net/p/octave/image/rev/7cf22a478792

I'm sorry. You pasted the code on the comment and I didn't notice the attached file. I copied the code from your comment into the file and made the commit with your name.

You did everything right, I just didn't notice the file.

Would be nice if you could follow the coding guidelines a bit better next time, i.e., use spaces between function names and brackets but not after variables and brackets used to index, e.g.:

this_is_a_function (these, are, arguments);
this_is_a_variable(these_are_indexes)

Since we use () both for indexing and calling functions, this helps distinguish them when reading. Also, no trailing whitespace. I also grouped the tests together since they were all sharing the sam einput.

It is done.

http://hg.code.sf.net/p/octave/image/rev/f044c717ad03

But please note that this is not meant to be the email for contact for help. It will probably only be used for copyright issues (which will hopefully not arise), important stuff so do not use an email that you do not check.

Also, I used the other email as author of the changeset. I changed the address on the source but on the author of the changeset. Would bw great if you cloned the image package repo and submitted a cset file next time. These are the instructions for Octave core but for the image package it's the same thing https://www.gnu.org/software/octave/doc/interpreter/Basics-of-Generating-a-Changeset.html

Thank you for the patch. I have pushed it as http://hg.code.sf.net/p/octave/image/rev/d54065343186

A good improvement would be to avoid the basic computations for each property. For example, when computing Orientation and Eccentricity, it could reuse the computed values of Major and Minor axis length instead of computing them again.

Why does you patch reimplements the orientation option? Is it fixing anything there? The orientation is not commented on the repository

http://hg.code.sf.net/p/octave/image/file/c5c645f29103/inst/regionprops.m

Here is a new version for the 4 "ellipse" properties in the regionprops.m file. (They are slightly improved with respect to the last version, now they are more accurate for very small regions.)

    case "majoraxislength"
        if (N > 2)
          warning ("regionprops: skipping majoraxislength for Nd image");
          break
        endif

        for k = 1:num_labels
          [Y, X] = find (L == k);

          if (numel(Y) > 1)
            % calculate (centralised) second moment of region
            C = cov ([X(:), Y(:)], 1);    % option 1 for normalisation with n instead of n-1
            C = C + 1/12.*eye(size(C,1)); % centralised second moment of 1 pixel is 1/12
            lambda = eig (C);
            retval (k).MajorAxisLength =4 * sqrt(max(lambda));
          else
            retval (k).MajorAxisLength = 1;
          endif
        endfor

     case "minoraxislength"
         if (N > 2)
          warning ("regionprops: skipping minoraxislength for Nd image");
          break
        endif

        for k = 1:num_labels
          [Y, X] = find (L == k);
          if (numel(Y) > 1)
            % see case majoraxislength for explanations
            C = cov ([X(:), Y(:)], 1);
            C = C + 1/12.*eye(size(C,1));
            lambda = eig (C);
            retval (k).MinorAxisLength =4 * sqrt(min(lambda));
          else
            retval (k).MinorAxisLength = 1;
          endif
        endfor

     case "eccentricity"
         if (N > 2)
          warning ("regionprops: skipping eccentricity for Nd image");
          break
        endif

        for k = 1:num_labels
          [Y, X] = find (L == k);
          if (numel(Y) > 1)
            % see case majoraxislength for explanations
            C = cov ([X(:), Y(:)], 1);
            C = C + 1/12.*eye(size(C,1));
            lambda = eig (C);
            major =  2 * sqrt(max(lambda));
            minor =  2 * sqrt(min(lambda));
            retval (k).Eccentricity = sqrt(1-(minor/major)^2);
          else
            retval (k).Eccentricity = 0; % a circle has 0 eccentricity
          endif
        endfor

     case "orientation"
        if (N > 2)
          warning ("regionprops: skipping orientation for Nd image");
          break
        endif

        for k = 1:num_labels
          [Y, X] = find (L == k);
          if (numel (Y) > 1)
            % see case majoraxislength for explanations
            C = cov ([X(:), Y(:)], 1);
            C = C + 1/12.*eye(size(C,1));
            [V, lambda] = eig (C);
            [max_val, max_idx] = max (diag (lambda));
            max_vec = V(:, max_idx);
            retval (k).Orientation = -(180/pi)  * atan (max_vec (2) / max_vec (1));
          else
            retval (k).Orientation = 0;
          endif
        endfor

As you can see, I've also added the Orientation feature to my code. Those 4 properties are consistent now. And I think they should be Matlab compatible as well. (It may be worth checking the results of the tests with a real Matlab nevertheless. I don't have access to it for the next months.)

And here are a few tests for those 4 new features:

a = eye(4);
t = regionprops(a, 'majoraxislength');
assert(t.MajorAxisLength, 6.4291,  1e-3);

b = ones(5);
t = regionprops(b, 'majoraxislength');
assert(t.MajorAxisLength, 5.7735 , 1e-3);

c = [0 0 1; 0 1 1; 1 1 0];
t = regionprops(c, 'majoraxislength');
assert(t.MajorAxisLength, 4.1633 , 1e-3);

a = eye(4);
t = regionprops(a, 'minoraxislength');
assert(t.MinorAxisLength, 1.1547 , 1e-3);

b = ones(5);
t = regionprops(b, 'minoraxislength');
assert(t.MinorAxisLength, 5.7735 , 1e-3);

c = [0 0 1; 0 1 1; 1 1 0];
t = regionprops(c, 'minoraxislength');
assert(t.MinorAxisLength, 1.8037 , 1e-3);

a = eye(4);
t = regionprops(a, 'eccentricity');
assert(t.Eccentricity, 0.98374 , 1e-3);

b = ones(5);
t = regionprops(b, 'eccentricity');
assert(t.Eccentricity, 0 , 1e-3);

c = [0 0 1; 0 1 1; 1 1 0];
t = regionprops(c, 'eccentricity');
assert(t.Eccentricity, 0.90128 , 1e-3);

a = eye(4);
t = regionprops(a, 'orientation');
assert(t.Orientation, -45 , 1e-3);

b = ones(5);
t = regionprops(b, 'orientation');
assert(t.Orientation, 0 , 1e-3);

c = [0 0 1; 0 1 1; 1 1 0];
t = regionprops(c, 'orientation');
assert(t.Orientation, 45 , 1e-3);

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

Sorry, I didn't know about the long history of those features.

Currently I do not have access to Matlab, so I won't be of any help for clarifying compatibility issues. Once I regain access to Matlab at the end of this year I could try to work on this.

In the source code file "regionprops.m" of the release image-2.2.2 the properties "orientation", "majoraxislength" and "minoraxislength" are included but commented out (and not listed in the all_props list at the beginning of the file). I found their output reasonable and useful, would it be possible to comment them in for the next release of the image package?

Additionally the property "eccentricity" could be easily implemented: with a=majoraxislength and b=minoraxislength it is definded as eccentricity=sqrt(1-(b/a)^2) .