1. Spectral image sensor unit for imaging an object having a movement relative to the sensor, an image of the object being projected along a path over the sensor resulting from said movement, the spectral sensor unit comprising at least two sets of light sensor elements, each element comprising a filter or other means of adapting the spectral response of the element, such that within each sensor set there are elements with at least two types of different spectral responses, the spectral responses in said at least two sensor sets being essentially identical, the sensor sets being arranged in the path direction such that the object image passes each sensor set so as to pass at least twice over each type of spectral response.