A novel approach for characterization of semiconductor pixel detectors using X-rays is presented. A precise gold grid placed in front of the sensor chip segments the incoming X-ray beam into a matrix of precisely defined micro-beams irradiating all pixels in well-defined positions. Analysis of the resulting moiré pattern allows evaluation of the charge sharing effect and determination of its influence on the spectrometric properties of the detector. As opposed to currently used single micro-beam studies realized at synchrotron sources, the whole pixel matrix is investigated at once. This offers a great tool for the investigation of charge sharing phenomena and verification of theoretical models used to describe these detectors. Similarly, such an absorption grid can be used for masking the pixel borders thus suppressing the charge sharing effect. As we demonstrate, this approach significantly improves the spectrometric properties of the pixelated detector at the cost of lower detection efficiency. This technique can be used for energy sensitive X-ray imaging of inanimate objects where the radiation dose does not present an issue.