y being combined to form one pixel and from this u2014 preferably by determining the median value u2014 an image signal value b belonging to this pixel is calculated the totality of the image signal values b calculated from the detector signal values d x y then forms a two dimensional x ray image which can finally be displayed on a monitor or be issued by a printer the apparatus has an erasing unit 20 with which after the read out of the x ray information stored therein the storage phosphor layer 1 is irradiated with erasing light 21 in order to totally erase any x ray information remaining in the storage phosphor layer 1 the erasing device 20 is illustrated in a strongly schematised manner in the example shown here and in addition to a suitable reflector arrangement comprises one or more light sources e g a lamp or light diodes for emitting erasing light 21 in a specific wavelength spectrum alternatively the erasing unit 20 can also comprise light sources which generate erasing light 21 in different wavelength spectra further possible embodiments of the erasing unit 20 are described in greater detail in publications u s pat no 7 633 078 b2 ep 1 895 325 a1 u s pat no 7 498 597 b2 ep 1 895 326 a1 and u s pat no 7 507 984 b2 ep 1 895 327 a1 the contents of which are herewith incorporated as part of the disclosure of preferred embodiments of the invention by this reference the erasing unit 20 can be disposed in different positions relative to the read out unit 2 and 4 to 6 in the example shown u2014 as viewed in the.