A medical system (10) and method measures hemoglobin level of a subject (38). A hemoglobin color scale (HbCS) (22) is projected into afield of view (FOV) (42) of an imaging system (12). The HbCS (22) includes a plurality of blood color regions (26a-f), each blood color region (26a-f) corresponding to a hemoglobin level and colored to represent the color of blood at the corresponding hemoglobin level. An image of blood of the subject (38), and the projected HbCS, is acquired using the imaging system (12).