# Encryption of 3D or Higher-Dimensional Images: A Review
## 2 Plenoptic Images
### Light Field Images  
Light field images are typically captured using a dense array of cameras, as can be seen in the illustration presented in Figure 1a, in which we have several cameras arranged in a two-dimensional plane. In the case of a light field image captured by a dense array of cameras, the result is an array of images, each providing the viewpoint and angle corresponding to its respective camera within the same scene. In Figure 1b, one observes an example of a light field image acquired by such a system of cameras.  
Another approach is employing a special camera with a single photosensitive sensor, called a lenslet camera, in conjunction with a microlens array, which samples light beams emanating from various directions. Light field images acquired using lenslet cameras [21] exhibit a raw format resembling what is commonly referred to as the fly's-eye pattern due to the acquisition method employed by these devices. Figure 2 presents a simplified schematic for capturing light information through a lenslet camera. It is important to note that between the objective lens and the photosensitive sensor there exists an array of microlenses. This arrangement allows for the capture of information from different directions originating from a single point. Consequently, the fly's-eye pattern manifests in the images obtained from such devices, as illustrated in Figure 3. It is possible to notice in the enlarged portion of Figure 3 the occurrence of the fly's-eye pattern, in which for each point in the scene we have a set of pixels, each one coming from a different angle. This visualization format, also known as microarrays, enables the representation of the light field image as a single two-dimensional image.  
For the sake of convenience, light field images can also be represented within a four-dimensional structure; the captured light beams are parameterized by the coordinates of their intersection with two planes [24]. The coordinate system is denoted by \((s,t)\) for the first plane and \((u,v)\) for the second. A light beam defined within this system first intersects the \(st\) plane at the coordinate \((s,t)\) and subsequently intersects the \(uv\) plane at the coordinate \((u,v)\), thereby being denoted as \(L(s,t,u,v)\). Consequently, instead of a single two-dimensional image composed of microarrays, a 4D light field can be represented as an array of 2D images. It is illustrated in Figure 4, where all possible views of the light field shown in Figure 3 can be visualized. This representation method is employed for images acquired using both dense camera arrays and lenslet cameras.  
Figure 1: **(a)** An illustration of a camera array used to capture light field images and (b) an image captured by such a system.  
Figure 4: Visualization of all views of a light field image captured by a lenslet device, where each view is referenced by a coordinate system \((s,t)\), along with an expanded central view, in which each pixel is referenced by a coordinate system \((u,v)\).  
Figure 3: Raw image obtained from a lenslet camera and an expanded portion of the same image.  
Figure 2: Schematic of light information captured in a lenslet camera.