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Imaging aims to create a correspondence between the distribution of light in an object plane, in which the objects of interest are placed, and in an image plane, where a sensor measures intensity. An imaging device is characterized by resolution, which determines how sharp is the correspondence between the two conjugate planes, and depth of field, which fixes the longitudinal distance range in which the object can move, while its image is still well focused on the sensor. Unfortunately, a natural tradeoff between resolution and depth of field entails that focusing a high-resolution image is much harder than focusing a low-resolution one. Moreover, standard imaging devices are not able to recover information on the out-of-focus planes after the acquisition. The goal of plenoptic imaging is to overcome this limitation, by retrieving combined information on both the spatial distribution and the direction of light in the scene of interest, which opens the possibility to refocus planes of the scene in a much wider range than the natural depth of field of the system, and also to change the point of view on the scene. Though plenoptic imaging is one of the most promising techniques for 3D imaging, in all the devices based on intensity measurements its advantages come at the expense of spatial resolution, which can no longer reach its diffraction limit. In this paper, we review the possibility to avoid loss of resolution by integrating second-order intensity correlation measurements in a simple single-lens imaging setup. The described device, based on the correlation plenoptic imaging (CPI) technique, enables one to perform either standard or plenoptic imaging, while keeping the resolution at the diffraction limit. We show that the proposed setup outperforms both standard imaging and first-order plenoptic imaging in terms of resolution and depth of field.
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