Controlling image size as a function of distance and wavelength in Fresnel-transform reconstruction of digital holograms

Abstract

A method for controlling the size of amplitude and phase images reconstructed from digital holograms by the Fresnel-transform method is proposed and demonstrated. The method can provide a constant reconstruction pixel width in the reconstructed image plane, independent of the recording and reconstruction distance. The proposed method makes it possible to maintain the size of an object for a sequence of digital holograms recorded at different distances and, therefore, to subtract phase maps for an object recorded at different distances. Furthermore, the method solves the problem of superimposition in multiwavelength digital holography for color display and holographic interferometry applications.

Speckle reduction of reconstructions of digital holograms using three dimensional filtering

“…The DH was interpolated by a factor of 4 in order to be able to sample at a scale that was significantly smaller than the the expected theoretical speckle size. For the direct reconstruction method interpolation of the reconstruction was achieved by zero padding the DH prior to reconstruction, whereas for the spectral method interpolation was achieved by zero padding the DH in the frequency domain using two DFT operations [37]. For the resolution chart hologram [see DH 1 in Table 2 for details of its parameters] the expected speckle size in the x and y directions is 7.16µm and 9.59µm, respectively.…”

Pulsed Full-Color Digital Holography with a Raman Shifter

“…The effects of varying sizes of the reconstructions from the color holograms were compensated by resizing the holograms based on the ratio of wavelengths for a fixed image distance using the relation (Ferraro, 2004):…”

“…The distance of the best-focused image is established by numerically focusing the hologram at various distances and then selecting the sharpest image. For the purposes of comparison, reconstructions from resized holograms are also plotted at the same reconstruction distance (Ferraro et al, 2004). The fixed distance condition corresponds to the reconstruction distance of the blue channel.…”

Three-dimensional Information and Refractive Index Measurement Using a Dual-wavelength Digital Holographic

“…Usually, scanning processes are necessary to measure the refractive indices distribution on the sample in previous work. To calculate the phase of the same point from a hologram with a different wavelength, one should resize the holograms [19][20]. Figure 2 shows a schematic of a dual-wavelength transmission holographic microscope.…”