A multispectral or thermal imager comprising a lens assembly, an array of IC chips that is arranged in a field of view of the lens assembly, each IC chip comprising an array of thermopile devices, and a filter assembly comprising one or more wavelength filters. The filter assembly comprises a respective wavelength filter for at least one of the three or more rows of IC chips. At least one wavelength filter is transparent in a portion of a wavelength range that passes through the lens assembly. The filter assembly is configured such that radiation of the same wavelength range passes to the rows of IC chips in the pair of non-adjacent rows, and such that the wavelength range that passes to the rows in the pair of non-adjacent rows is different from a wavelength range that passes to the one or more rows other than the pair of non-adjacent rows.