function f = retroprojection(sinogramme, theta, n_rayons, n_lignes, n_colonnes)

    n_theta = length(theta);
    f = zeros(n_lignes, n_colonnes);

    theta = theta * pi / 180;

    for k=1:n_theta

        angle = theta(k);

        for i=1:n_lignes
            for j=1:n_colonnes

                x = j - n_colonnes/2;
                y = -i + n_lignes/2;

                t = x * cos(angle) + y * sin(angle);
                t = t + n_rayons/2;
                t = min(max(round(t),1), n_rayons);

%                 if t > 501 || t <= 0
%                     continue
%                 end

                f(i, j) = f(i, j) + sinogramme(t, k);

            end
        end
    end

    f = f / n_rayons;

end