As the architectural complexity of integrated circuits and functional nanomaterials advances into the atomic-scale regimes, high-resolution transmission electron microscopy (TEM) has become an essential tool in validating the structure of nanomaterials and devices. In contrast to conventional TEM imaging, which only provides projected 2D information, electron tomography is a powerful tool that can probe the 3D internal structure and chemistry of materials at the nanoscale and the atomic scale. [1] Due to its high resolution, it has been widely used in biological, [2,3] physical, [4,5] and materials science [6-10] applications. Recently, with the development of discrete tomography [11-13] and atomic-scale electron tomography, [14-18] deciphering the structure of materials atom by atom has become possible. Electron tomography renders 3D reconstruction of an object by taking a series of 2D projections from a wide range of orientations. Ideally, projection images from À90 to þ90 around a fixed axis are needed to render a perfect 3D reconstruction. [19] However, due to the limited space in an electron microscope or shadowing from the holder/sample/ support, it is hard to obtain projections for the full tilt range in many conditions. With a specialized tomography holder, images from À70 to þ70 can be obtained in most TEMs, whereas in liquid-cell tomography, the tilt range is very limited to typically <30 , because the liquid flow holders are much bulkier. [20] The limited tilt range unavoidably leads to a "missing wedge" of information, which renders artifacts in the reconstructed tomograms. These artifacts introduced by the missing wedge reduce the resolution and reliability of the reconstructed tomograms and, sometimes, can even lead to serious misinterpretations. [6] So far, the missing-wedge problem has been the main source of systematic error that limits the application of electron tomography. Mathematically speaking, when there are insufficient number of projections, the inverse problem of tomography is ill-posed, because the solution is non-unique. Therefore, to constrain the solution space, strong priors need to be used to regularize the problem. For example, total variance minimization (TVM) combines iterative reconstruction and regularization of total variance to recover the lost information and reduces the artifacts introduced by the missing wedge. [21,22] This method is inspired by compressive sensing, [23,24] and it essentially deploys the sparsity constraint in the gradient domain of the tomogram. Some caveats of TVM are that it is not parameter-free and is also computationally expensive. Keeping these aside, the real problem of TVM or any generalized TVM approach is that they are bound to one regularization that promotes one prior constraint on the solution, which may or may not be suitable for the object of interest. For example, TVM promotes piecewise constants, rendering cartoon-like tomograms lacking gradient details.