Improving the Quality of Digital Holographic Images Using Subpixel Spatial Shifts

A new method for improving the quality of images reconstructed from digital holograms is considered. It is based on spatial subpixel shifts, i.e., shifts by a certain value smaller than the resolution provided by the recording devices. In digital holography, photodetector arrays are used as a medium for recording holograms. The resolution is determined by the type of the photodetector arrays. Holograms are recorded using a camera with a photodetector array with a resolution of 9000× 6752 and a single element size of 0.86× 0.86 μ m. The size of the photodetector array is 7.7× 5.8 mm, the spatial resolution of such devices is about 500–1000 lines per mm. This already makes it possible to obtain digital holograms. However, to improve the quality of reconstructed images, it is necessary to increase the hologram resolution during registration. A device for introducing a spatial subpixel shift of the photodetector array is used to increase the resolution. The insufficient resolution of the arrays is compensated for using subpixel spatial shifts. The shift is performed along the X and Y coordinates by 430 nm, which amounted to half the size of one array element. The digital hologram size increases fourfold ( 18\,000× 13\,504 pixels). Images are reconstructed using a fast Fourier transform. To speed up the process, a graphics accelerator is used to reconstruct images from holograms.