Comparison between a planetary transit and blended eclipsing binary. Panel a: uncontaminated transit by a planet with radius ratio of 0.1 observed in the i′ band, panelb: faint M-dwarf transited by an object with a radius ratio of 0.32 strongly contaminated by a G star (c = 0.9, i.e. 10% of the total flux comes from the M dwarf, and 90% from the G star) leading to an apparent radius ratio of 0.1 in the i′ band, and panel c: same contaminated transit observed in g′, r′, i′, and z′ bands.