A method and apparatus for generating a digital X-ray image is disclosed. The method comprises starting an exposure period wherein an array of X-ray receptors are exposed to X-ray radiation, varying the energy of the X-ray radiation during the exposure period and generating a data value for each receptor in the array of X-ray receptors. Each data value corresponds to the time elapsed between the start of the exposure period and the time at which the magnitude of the X-ray radiation incident upon the corresponding receptor passes a reference value. The data values are processed to generate an image. The apparatus includes an X-ray generator, a clock, an array of X-ray receptors, a comparator, a storage medium, and a processor.