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Deflectometric techniques

: Pak, Alexey; Höfer, Sebastian; Burke, Jan

Frontpage ()

EP 3582183 A1: 20180611
Patent, Electronic Publication
Fraunhofer IOSB ()

There is described an apparatus (50, 52, 110, 160) for deriving properties of an object (53) on the basis of:- a sequence (170) of reference patterns (70) displayed by a reference device (56), the sequence of reference patterns (70) being displayed at subsequent time instants by the reference device (56) so that light emitted by the reference device (56) is incident on the object (53);- a sequence (190) of images (90), the images (90) being obtained at time instants from the light emitted by the reference device (56) according to the reference patterns (70) and transported to a sensing device (54) via optical paths (57a, 57b, 57', 57", 58"') which involve inner and/or outer reflections from the surface (53a, 53b) and/or propagation through the volume of the object (53),the apparatus being configured, for at least one image pixel position in each of the images (90) of the sequence (190) of images (90), to:- perform a processing of images to obtain a similarity function (121) between:∘ a plurality of reference codes, each reference code being associated to one reference pixel position in the reference patterns, each reference code carrying information on the evolution of the optical radiation intensity of the reference device position (p) modulated by the value of the reference pattern pixel at the reference pixel position during the time instants; and∘ an acquired code associated to the image pixel position, the acquired code carrying information on the evolution, in the sequence of images, of the optical radiation intensity acquired for the image pixel position;- find (122):∘ at least one peak in the similarity function, the peak being a local peak or a global peak between the values of the similarity function; and∘ for at least one found peak, a maximizing reference pixel position (93, 94) associated to the at least one peak; and- for each found peak (123):∘ associate the maximizing reference pixel position to the image pixel position.