In the field of radiological diagnostics, especially for the computed tomography a large number of photodetector elements (so called Pixels) is needed to assemble a large-area X-Ray-sensitive detector. These pixels should provide very high sensitivity, a very large dynamic range and a high signal-to-noise-ratio. Moreover, an in-pixel digitization of the signals is desired. To meet these specifications, a digital CMOS-Pixel comprising a special type of photodiode and a single-loop sigma-delta-modulator was developed, theoretically analyzed, fabricated and characterized. A matrix of 4x4 digital CMOS-pixels with each of them consuming an area of 1mm² has been fabricated. For further signal processing the concept of a multichannel decimation filter is presented.