A multi-spectral X-ray detector (10a, 10b, 10c) comprising: - a first X-ray detector configured to receive incident X-ray radiation; - a structured spectral filter configured to receive intermediate X-ray radiation propagating out of the first X-ray detector; and - a second X-ray detector axially aligned with the first X-ray detector and the structured spectral filter, and configured to receive filtered intermediate X-ray radiation propagating out of the structured spectral filter; wherein the first X-ray detector comprises a contiguous plurality of pixels forming a superpixel (SP 1, SP 2, SP 3, SP 4); wherein the second X-ray detector comprises a first plurality of pixels (P 11, P 21, P 31, P 41) and a second plurality of pixels (P 12, P 22, P 32, P 42), each aligned to receive a portion of the filtered intermediate X-ray radiation having passed through the superpixel; wherein the structured spectral filter comprises a filter structure aligned with pixels of the superpixel, and comprising a first region aligned with the first plurality of pixels of the second X-ray detector, and a second region aligned with the second plurality of pixels of the second X-ray detector, wherein the first region is configured to alter the spectrum of the intermediate X-ray radiation incident on the first plurality of pixels of the second X-ray detector to form the filtered intermediate X-ray radiation; and wherein the contiguous plurality of pixels forming the superpixel of the first X-ray detector are in alignment with at least the first and the second pluralities of pixels of the second X-ray detector, so as to provide, when the multi-spectral X-ray detector is in use, at least three X-ray spectra per superpixel (SP 1, SP 2, SP 3, SP 4). - a first X-ray detector configured to receive incident X-ray radiation; - a structured spectral filter configured to receive intermediate X-ray radiation propagating out of the first X-ray detector; and - a second X-ray detector axially aligned with the first X-ray detector and the structured spectral filter, and configured to receive filtered intermediate X-ray radiation propagating out of the structured spectral filter; wherein the first X-ray detector comprises a contiguous plurality of pixels forming a superpixel (SP 1, SP 2, SP 3, SP 4); wherein the second X-ray detector comprises a first plurality of pixels (P 11, P 21, P 31, P 41) and a second plurality of pixels (P 12, P 22, P 32, P 42), each aligned to receive a portion of the filtered intermediate X-ray radiation having passed through the superpixel; wherein the structured spectral filter comprises a filter structure aligned with pixels of the superpixel, and comprising a first region aligned with the first plurality of pixels of the second X-ray detector, and a second region aligned with the second plurality of pixels of the second X-ray detector, wherein the first region is configured to alter the spectrum of the intermediate X-ray radiation incident on the first plurality of pixels of the second X-ray detector to form the filtered intermediate X-ray radiation; and wherein the contiguous plurality of pixels forming the superpixel of the first X-ray detector are in alignment with at least the first and the second pluralities of pixels of the second X-ray detector, so as to provide, when the multi-spectral X-ray detector is in use, at least three X-ray spectra per superpixel (SP 1, SP 2, SP 3, SP 4).