Distribution of extragalactic objects in the log (f_x/f_r) versus g − i diagram according to L_X. Black;  > 10⁴⁵, red 10⁴⁴ to 10⁴⁵, green 10⁴³ to 10⁴⁴, blue 10⁴² to 10⁴³, yellow 10³⁸ to 10⁴². We only show SDSS entries with a probability of identification with an X-ray source higher than 90%, g and i magnitudes brighter than 22.2 and errors on g − i < 0.2.