use axes coordinate to generate an image without plotting it, in Matlab

I have an image full of objects 开发者_运维知识库of the shape of an ellipse. I need to design an ellipse for each object that is the best fit for the object itself. I have found a code that helps me to plot the ellipses on the image here.

I have changed the final part saving x and y in a 3D matrix (one dimension for x, the other for y, and the 3rd for the number of objects). Because this code is in a for loop, I do not want to generate the figure plot ellipses on top of it, save it and upload with imread to pass it to the rest of the code.

Is there a way to convert this 3D matrix in a bw image full of the fitting ellipses in the correct position in the image?

Ellipses are drawn on top of the existing figure because of the hold on statement after the image is shown using imshow. So, instead of this:

imshow(bw)
hold on

Simply create a new figure using the figure statement:

figure

[Edit]

Ok, first of all, storing only (x, y) gives you ellipse centers only. To draw an ellipse, you will also need to store its majos/minor axis size (a, b) and its orientation angle (theta).

I would simply reuse the loop that you already have, but replace plot with simply setting a bw image pixel to 1 for each coordinate:

% get image dimensions
dim = size(bw);

% preallocate a blank bw image
target = false(dim);

% for each ellipse
for k = 1:length(s)

    % this part remains the same:
    xbar = s(k).Centroid(1);
    ybar = s(k).Centroid(2);

    a = s(k).MajorAxisLength/2;
    b = s(k).MinorAxisLength/2;

    theta = pi*s(k).Orientation/180;
    R = [ cos(theta)   sin(theta)
         -sin(theta)   cos(theta)];

    xy = [a*cosphi; b*sinphi];
    xy = R*xy;

    x = xy(1,:) + xbar;
    y = xy(2,:) + ybar;

    % ----------
    % but replace plot(x,y) with this:

    % limit to image dimensions (1:256)
    x(x<1) = 1; x(x>dim(1))=dim(1);
    y(y<1) = 1; y(y>dim(2))=dim(2);    

    % set those pixels to 1
    target(sub2ind(dim, round(x),round(y))) = 1;

end

imshow(target);

Right now, there are ellipses which are half outside the image boundaries. That's why their x,y coordinates need to be limited to (1:256); otherwise you get an out-of-range error. You still need to rethink whether these ellipses should be removed entirely, or drawn partially as done here.