A digital detector for radiography and fluoroscopy. The detector comprises a large area, flat panel which easily fits into the conventional X-ray room bucky tray. The detector utilizes a layer of photoconductor (i.e. a-Se in the preferred embodiment) to detect X-rays and convert the X-ray energy to charge, and an active matrix TFT array in the form of a very large area integrated circuit, for readout of the charge. A dual gate structure is used for the TFT array wherein the top gate is formed as an extension of the pixel electrode, so as to provide high voltage protection of the TFT. An integrated pixel storage capacitor is provided for enhanced absorption of X-ray energy with low pixel voltage, low leakage current and a large charge leakage time constant. In the preferred embodiment, the integrated pixel storage capacitor is created by overlapping the pixel electrode with an adjacent gate line or a separate groundline of the active matrix readout array. Image charge collection efficiency is enhanced in the imager of the present invention by manipulating the electric field distribution in the photoconductor layer so that image charges land on the pixel electrodes, and not on the TFT readout devices. Also, a photo-timer is integrated into the imaging detector for measuring X-ray exposure.