1974 年 43 巻 12 号 p. 1213-1218
A hologram conversion technique by a computer method is proposed and an experiment to convert Fresnel-transform holograms into Fourier-transform holograms is conducted. A photographically recorded acoustical hologram constructed with a 15 kHz sound-wave is sampled with 64×64 sampling points and quantized into 5 levels for numerical processing. The hologram conversion is done by calculating the product of the Fourier spectra of the Fresneltransform hologram with a propagation function. The calculated Fourier-transform hologram is displayed by an X-Y plotter or a line printer and reduced photographically for optical image reconstruction. Images are reconstructed by performing the Fourier transform of the converted hologram in a suitable optical Fourier transform configuration. Some discussions on this numerical hologram conversion technique are conducted with reference to the experimental results.