Image Quality Evaluation of a Computer-Generated Phase Hologram
Quality of reconstructed image from computer-generated phase hologram is evaluated objectively on its peak signal-to-noise ratio and brightness.
Hologram can record and reconstruct or playback an optical wavefront on the hologram plane. It uses interference between two waves, an object wave from the object to be recorded and a reference wave. The interference intensity pattern is recorded on a photosensitive material. Computer-generated hologram (CGH) simulates this optical phenomenon in a computer (Lohmann and Paris 1967). CGH is widely used to show not only for 2D images but also complex 3D images. Image quality of the reconstructed image from CGH is usually evaluated subjectively. For example, an observer compares two images and scores. Here shows basic research to evaluate reconstructed image quality of phase-type CGH objectively on its peak signal-to-noise ration and brightness (Yoshikawa and Yamaguchi 2015).
Calculation Without the Object Self-Interference
Numerical Reconstruction of Phase Hologram
Then t(X,Y) is inverse Fourier transformed to obtain the reconstructed image. In the case of a sine-wave phase grating, the maximum diffraction efficiency of 33.8% is obtained at Δφ = 0.59. Therefore, this value is used unless denoted.
The diffraction efficiency (DE) is defined as the ratio of the intensities of the reconstructed image and the illumination light. It gives the brightness of the reconstructed image. In the numerical experiments, the reconstructed image intensity is obtained by summing up all intensities in the reconstructed image area as same size and position of the original image in the input image plane.
Peak Signal-to-Noise Ratio
Numerical Experimental Results
Conclusion and Discussion
Image quality of phase CGH is evaluated objectively on the diffraction efficiency and the peak signal-to-noise ratio. For the transmission phase hologram, although it is obtained over ten times of diffraction efficiency against amplitude hologram (DE = 0.77%, PSNR = 38.9 dB), PSNR is not as good as that of the amplitude hologram. Since the evaluated hologram is very simple phase hologram, it is expected to evaluate other type of phase hologram.
- Yoshikawa, H.: Image Quality Evaluation of a Computer-Generated Hologram, OSA topical meeting on Digital Holography and 3D Imaging. Shanghai, OSA (2015)Google Scholar
- Yoshikawa, H., Yamaguchi, T.: Image quality evaluation of a computer-generated phase hologram. In: 10th International Symposium on Display Holography, paper 4–4 (2015)Google Scholar