An apparatus to facilitate generation of a light map sensitive to a partially or totally specular surface of an object under inspection, the apparatus including: (a) a screen conforming substantially to a self-sliding surface that is movable relative to the object by sliding motion parametrized by a slide parameter which identifies a position of the screen within its set of positions traversable by the sliding motion, wherein the screen has a latitude and longitude coordinate system such that the sliding motion is longitudinal, characterised in that the screen has a leading edge and a trailing edge which are spaced from one another across a longitudinal dimension of the screen and the sliding motion is such that the trailing edge follows the leading edge on a stationary notional surface between respective start and end positions of the screen, wherein the stationary notional surface that is traversed both by the screen's leading edge and by the screen's trailing edge during the sliding motion of the screen is an encoded scene surface , wherein camera light emulating or passing through the encoded scene surface receives a reflection from at least part of the surface of the object. (b) a latitude-encoding graphic carried by the screen in accordance with its intrinsic latitude and longitude coordinate system, wherein the latitude-encoding graphic consists of latitudinally-varying longitudinal slices, which are latitude codewords, (c) at least one camera , held in a fixed spatial relationship relative to the object, for capturing successive frames of the object during said relative sliding motion of the screen, and (d) a computing device that accepts data of the captured frames for storage or processing, wherein light emanating from any scene point in the encoded scene surface, as a function of the slide parameter, is describable by the scene point's latitude's codeword shifted according to the scene point's longitudinal position in the encoded scene surface. (a) a screen conforming substantially to a self-sliding surface that is movable relative to the object by sliding motion parametrized by a slide parameter which identifies a position of the screen within its set of positions traversable by the sliding motion, wherein the screen has a latitude and longitude coordinate system such that the sliding motion is longitudinal, characterised in that the screen has a leading edge and a trailing edge which are spaced from one another across a longitudinal dimension of the screen and the sliding motion is such that the trailing edge follows the leading edge on a stationary notional surface between respective start and end positions of the screen, wherein the stationary notional surface that is traversed both by the screen's leading edge and by the screen's trailing edge during the sliding motion of the screen is an encoded scene surface , wherein camera light emulating or passing through the encoded scene surface receives a reflection from at least part of the surface of the object. (b) a latitude-encoding graphic carried by the screen in accordance with its intrinsic latitude and longitude coordinate system, wherein the latitude-encoding graphic consists of latitudinally-varying longitudinal slices, which are latitude codewords, (c) at least one camera , held in a fixed spatial relationship relative to the object, for capturing successive frames of the object during said relative sliding motion of the screen, and (d) a computing device that accepts data of the captured frames for storage or processing, wherein light emanating from any scene point in the encoded scene surface, as a function of the slide parameter, is describable by the scene point's latitude's codeword shifted according to the scene point's longitudinal position in the encoded scene surface. <EOS>