has different attenuation properties for different X-ray energy levels. Whenever a single X-ray energy value is desired the range of energies within the beam can be narrowed by applying filters at the X-ray source [@Buzug]. Some detectors are capable of separating the incoming photons into energy bins while counting (e.g. HEXITEC [@HEXITEC]). In these cases spectral or multi-channel projection data is acquired, providing additional information about the object at different energies. Compared to the single-channel setting, where each material has a single attenuation value in the reconstructed image, in the multi-channel setting the attenuation value for each material varies along the channels. In this way, a tomographic dataset of the object is acquired for each channel, where the attenuation value of the materials changes throughout these datasets. This multi-channel imaging can potentially yield extra information about the materials. With more materials in the object, especially with similar attenuation features at a fixed energy, having data from multiple channels enables a better separation during segmentation. A conceptual example of this is shown in Figure \[fig:Separation\]. It is hard to separate points based on their attenuation values in a one-dimensional energy space. For instance, the right side of the blue area might 