The X-ray transmission technology is commonly used in inspection of cargos in a container in places such as airports, customs etc. The X-ray transmission technology utilizes a linear detector array to obtain a two-dimensional transmission image of the container. For example, X-rays are collimated to form a fan-shaped ray beam, which is transmitted through an inspected object for detection. When the object is stationary, the detector receives only a one-dimensional projection of the object on a ray layer. When the object moves in a direction perpendicular to the ray layer, all parts of the object sequentially pass through the ray beam, and the detector obtains a two-dimensional projection image of the whole object by line scanning. However, in the inspection manner described above, projections of the object in the container in a depth direction overlap together, which results in a loss of depth information. Especially for materials with light atomic numbers such as explosives and dangerous articles etc., grayscale attenuation after X-ray transmission is not obvious enough, which seriously affects recognition and identification of features such as a shape, a position etc. of such an object.
Common measures which are currently available for acquiring a three-dimensional transmission image are CT tomography and stereo matching technology etc. The CT tomography technology is complicated and expensive, and has a long imaging time, which limits its application in industrial real-time detection. In a process of stereo matching for an complex object, grayscale reconstruction and boundary processing are complex, the calculation complexity is also very large, and therefore the stereo matching is difficult to be applied in practice. Therefore, it is necessary to study other technologies to acquire three-dimensional imaging information of the object in the container.