function [directions] = etalonnage(spheres, exterieur_masque, centre, rayon)

    taille_noyau = round(rayon/20);
    triangle = @(n)(1+n-abs(-n:n))/n;

    [height, width, N_photo, N_sphere] = size(spheres);
    
    directions = zeros(3, N_photo);
    for p=1:N_photo
        for s=1:N_sphere
            % recup info sphere
            image_sphere = spheres(:,:,p,s);

            % filtrage
            image_filtree = conv2(triangle(taille_noyau), triangle(taille_noyau), image_sphere, 'same');
            image_filtree = image_filtree .* ( 1 - exterieur_masque);

            % recup point brillant
            [~, I] = max(image_filtree, [], 'all');

            % recup des coords
            xc = centre(2);
            yc = centre(1);
            [x, y] = ind2sub([height, width], I);

            % calcul de la normale
            normal = [ x-xc, y-yc, 0 ];
            normal(3) = sqrt(rayon^2 - normal(1)^2 - normal(2)^2);
            normal = normal / norm(normal');

            % calcul de la direction
            axe_optique = [0, 0, 1];
            direction = 2 * (axe_optique * normal') * normal - axe_optique;

            directions(:, p) = directions(:, p) + direction';
        end
        directions(:, p) = directions(:, p) / N_sphere;
        directions(:, p) = directions(:, p) / norm(directions(:, p));
    end
end