X-ray transmission radiograms of Aluminum alloy contain relatively low contrast features induced by variations of the material chemical composition. Generally, these variations are strongly connected with grains of the metal, where these differ from each to other. Although grains of the studied material have typically dimensions of tens of micrometers only, the material variations can enable the observation of geometry and orientations of grains in the specimen volume employing advanced X-ray micro tomographic method. Analysis of such tiny structures requires high dynamic range of acquired radiograms with high signal to noise ratio and appropriate geometrical magnification. These requirements can be fully satisfied by using the pixelated single photon counting device Medipix, a precise micro-tomographic setup and appropriate data processing. Results will be demonstrated with an Aluminum alloy bar specimen.