1. A spectral camera for producing a spectral output, the spectral camera comprising: an objective lens for producing an image; an array of lenses for producing optical copies of segments of the image on different optical channels; an array of filters for the different optical channels and having an interleaved spatial pattern of different passbands across the array; and one or more sensor arrays arranged to detect the copies of the image segments on the different filtered optical channels, the interleaved spatial pattern of the array of filters being arranged so that detected segment copies of spatially adjacent optical channels have different passbands and represent segments of the image which partially overlap each other, and so that at least some of the detected segment copies of the same passband on spatially non-adjacent optical channels represent segments of the image which are adjacent and fit together, wherein at least part of the interleaved spatial pattern comprises segments of width of at least N 1 filters and height of at least N 2 filters and the overlap of spatially adjacent channels in this part of the interleaved spatial pattern is arranged to be by a factor of 1 - 1 /N 1 in a width direction and by a factor of 1 - 1 /N 2 in a height direction.