Recently, a novel look-up table (N-LUT) method to dramatically reduce the number of pre-calculated interference
patterns required for generation of digital holograms was proposed. In this method, the number of the fringe patterns to
be stored in the LUT can be dramatically reduced by employing a new concept of the principal fringe pattern (PFP). In
this method, the fringe patterns for other object points on each image plane can be obtained by simply shifting this precalculated
PFP according to the displaced location values from the center to those points and adding them together.
Fringe patterns for all object points located on each image plane can be generated by adding the shifted versions of the
PFP. Therefore, the final CGH pattern for an object volume can be obtained by overlapping all PFPs generated on each
depth-dependent image plane. Therefore, the size of LUT is determined by the amount of shift of the PFP. But, if the
resolution of object is increased, the size of PFP is increased. Thus the size of LUT is increased. And also, if the pixel
pitch of hologram is decreased, the amount of shift is increased. Thus the size of LUT is also increased. Therefore, in this
paper, we propose the memory reduction method using the relation of pixel pitch of hologram and reconstruction
distance. That is, size of PFP is reduced by controlling of the distance of object and pixel pitch while maintaining the
quality of the video. Some experiments with a test 3-D object are carried out and the reduction ratio of LUT is analyzed.