In Cone Beam Radiography, raw digital data for reconstruction is obtained from:

All computed tomographic (CT) scanners consist of an X-ray source and detector mounted on a rotating gantry. During rotation of the gantry, the X-ray source produces radiation, while the receptor records the residual X-rays after attenuation by the patient’s  tissues. These recordings constitute the “raw data” that is reconstructed by a computer algorithm to generate cross-sectional images. The basic component of these grayscale images is the picture element (pixel) values. The grayscale value or intensity of each pixel is related to the intensity of the photons incident on the detector. Although providing similar images, CBCT imaging represents a separate evolutionary arm to CT imaging employing multidetector computed tomographic (MDCT) imaging equipment.  Reference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 184