Research project
Crepe and Stamp method
One of the most efficient approaches for fast CGH calculation is a look-up table (LUT), which precalculates the wavefronts of point light sources (PLSs); however, enormous memory space for LUT is required. Crepe and Stamp method is an algorithm for reducing the required memory space for LUT with effective compression and decompression techniques using computer graphics (CG) techniques for drawing digital circles. Our method can compress required memory space to 1/1000 compared to conventional LUT method, and can calculate 2-9 times faster than conventional CGH calculation.

Utilizing a circular symmetry feature of a wavefront

A wavefront of a PLS created on a planar surface has a circular symmetric shape as shown in the left picture. In our method, the wavefronts are compressed to the data on a line and decompressed by drawing concentric circles using CG techniques. Because the CG techniques can draw digital circles only with integer operation, our method effectively decompresses a wavefront. In addition, our method includes a compensation method for quantization error that occurs when drawing concentric circles. Therefore, the image quality is sufficient.

Fast drawing algorithm for concentric circles

To increase the calculation speed, we should avoid a random memory access occurred when drawing concentric circles on circumferential direction. We developed a recurrence relation-based algorithm for drawing concentric circles. Our method calculates the radial distribution of concentric circles (as shown in the left picture) along the x-axis with minimal computational cost and copies the data. Because the efficiency of memory access increases when data are written or read along the x-axis, our method effectively decompress the wavefronts.

References

  1. Takashi Nishitsuji, Tomoyoshi Shimobaba, Takashi Kakue, Nobuyuki Masuda, Tomoyoshi Ito, "Fast calculation of computer-generated hologram using circular symmetry of zone plate", Optics Express, 20, 27496-27502 (2012). [link]
  2. Takashi Nishitsuji, Tomoyoshi Shimobaba, Takashi Kakue, Tomoyoshi Ito, "Fast calculation of computer-generated hologram using run-length encoding based recurrence relation," Optics Express, 23, 9852-9857 (2015). [link]