Patent ID: 7830521

Claim:
A detection apparatus comprising: an acquisition unit that acquires distribution information indicating a light intensity distribution of a light beam which is totally reflected at an interface of an optically transparent member, the light beam being incident at a plurality of angles to the optically transparent member, which has transparency to the light beam, such that the light beam is totally reflected at the interface of the optically transparent member; a derivation unit that performs a spatial frequency resolution on the light intensity distribution indicated by the distribution information acquired by the acquisition unit, to thereby derive the light intensity distribution of each spatial frequency of the light beam; and a detection unit that compares the light intensity distribution derived by the derivation unit, with a threshold value predetermined for each spatial frequency, to thereby detect a detection precision of a dark line position, wherein: the derivation unit derives the light intensity distribution of each spatial frequency by determining the light intensity distribution of a moving average of each predetermined width from the light intensity distribution indicated by the distribution information and by determining a difference between the light intensity distribution of the moving average and the corresponding light intensity distribution indicated by the distribution information, and determines a difference between the maximum and the minimum of the difference, which processing is performed a plurality of times while varying the width, to thereby derive a noise volume of each spatial frequency contained in the light intensity distribution indicated by the distribution information; and the detection unit compares each noise volume derived by the derivation unit with a threshold value that is predetermined for each width when the noise volume is derived, to thereby detect the detection precision of the dark line position.