  In this theoretical study, the author firstly discusses the wave interference
of Bragg diffraction inside 3D crystal, followed by quantum mechanical
interpretation on the diffraction process, and proves that the interference
fringe between Bragg diffraction and the incident beam is identical to the
lattice plane. By introducing the beam expander concept, we may explain the
image projection mechanism of Bragg diffractions propagating through TEM:
Transmission Electron Microscope. In practice, we will take projection images
at zone axes, because of its symmetric high-density diffractions associated
with flat Ewald sphere and minimum overlap with the neighboring molecules. By
precessing the illuminating beam around the zone axis, and introducing annular
objective aperture, we select only the kinematic Bragg diffractions which
correctly contribute to the real image reconstruction on the 2D electron
detector. The outcome should be a positive contrast, clean image with no
dynamical diffractions nor Moir\'e patterns. Importantly, the image should be
insensitive to the defocus, and the spatial resolution may not be limited by
the spherical and the chromatic aberrations of objective lens. Therefore, the
imaging of small molecules, such as, the drug structure will be
straightforward. By taking multiple projection images at the different zone
axes from many micro-crystals, or from surrounding thin edges of a large
crystal, we may reconstruct 3D structure of the larger protein complex in
atomic resolution.
