Fast compression of computer-generated holographic images based on a GPU-accelerated skip-dimension vector quantization method

A method for fast and low bit-rate compression of digital holograms based on a new vector quantization （VQ） method known as the skip-dimension VQ （SDVQ） is proposed. Briefly, a complex hologram is converted into a real off-axis hologram, and partitioned into a set of image vectors. The image vectors are passed into a graphic processing unit （GPU）, and compressed through SDVQ into a set of code indices considerably smaller in data size than the source hologram. Experimental evaluation reveals that our scheme is capable of compressing a digital hologram to a compression ratio of over 500 times, in approximately 20-22 ms.

Minimizing the effects of unmodulated light and uneven intensity profile on the holographic images reconstructed by pixelated spatial light modulators

A simple and effective approach is proposed to minimize the effect of unmodulated light and uneven intensity caused by the pixelated structure of the spatial light modulator in a holographic display. A more uniform image is produced by purposely shifting the holographic images of multiple reconstructed lights with different incident angles from the zero-diffraction-order and overlapping those selected different orders. The simulation and optical experimental results show that the influence of the zero-diffraction-order can be reduced, while keeping the good uniformity of the target images by this new approach.

Electromagnetic holographic sensitivity field of two-phase flow in horizontal wells

Electromagnetic holographic data are characterized by two modes, suggesting that image reconstruction requires a dual-mode sensitivity field as well. We analyze an electromagnetic holographic field based on tomography theory and Radon inverse transform to derive the expression of the electromagnetic holographic sensitivity field （EMHSF）. Then, we apply the EMHSF calculated by using finite-element methods to flow simulations and holographic imaging. The results suggest that the EMHSF based on the partial derivative of radius of the complex electric potential φ is closely linked to the Radon inverse transform and encompasses the sensitivities of the amplitude and phase data. The flow images obtained with inversion using EMHSF better agree with the actual flow patterns. The EMHSF overcomes the limitations of traditional single-mode sensitivity fields.

3D displays: toward holographic video displays of 3D images

As the fiat panel displays （Liquid Crystal Displays, AMOLED, etc.） reach near perfection in their viewing qualities and display areas, it is natural to seek the next level of displays, including 3D displays. There is a strong surge in 3D liquid crystal displays as a result of the successful movie Avatar. Most of these 3D displays involve the employment of special glasses that allow one view perspective for each of the eyes to achieve a depth perception. Such displays are not real 3D displays. In fact, these displays can only provide one viewing perspective for all viewers, regardless of the viewer＇s position. In addition, a fundamental viewing problem of focusing and accommodation exist that can lead to discomfort and fatigue for many viewers. In this paper, the authors review the current status of stereoscopic 3D displays and their problems. The authors will also discuss the possibility of using fiat panels for the display of both phase and intensity of video image information, leading to the ultimate display of 3D holographic video images. Many of the fundamental issues and limitations will be presented and discussed.

Harnessing the magic of light:spatial coherence instructed swin transformer for universal holographic imaging

.Holographic imaging poses significant challenges when facing real-time disturbances introduced by dynamic environments.The existing deep-learning methods for holographic imaging often depend solely on the specific condition based on the given data distributions,thus hindering their generalization across multiple scenes.One critical problem is how to guarantee the alignment between any given downstream tasks and pretrained models.We analyze the physical mechanism of image degradation caused by turbulence and innovatively propose a swin transformer-based method,termed train-with-coherence-swin(TWC-Swin)transformer,which uses spatial coherence(SC)as an adaptable physical prior information to precisely align image restoration tasks in the arbitrary turbulent scene.The light-processing system(LPR)we designed enables manipulation of SC and simulation of any turbulence.Qualitative and quantitative evaluations demonstrate that the TWC-Swin method presents superiority over traditional convolution frameworks and realizes image restoration under various turbulences,which suggests its robustness,powerful generalization capabilities,and adaptability to unknown environments.Our research reveals the significance of physical prior information in the optical intersection and provides an effective solution for model-to-tasks alignment schemes,which will help to unlock the full potential of deep learning for all-weather optical imaging across terrestrial,marine,and aerial domains.

Holographic imaging of full-color real-existing three-dimensional objects with computer-generated sequential kinoforms

We propose a computational method for generating sequential kinoforms of real-existing full-color three- dimensional （3D） objects and realizing high-quality 3D imaging. The depth map and color information are obtained using non-contact full-color 3D measurement system based on binocular vision. The obtained full-color 3D data are decomposed into multiple slices with RGB channels. Sequential kinoforms of each channel are calculated and reconstructed using a Fresnel-diffraction-based algorithm called the dynamic- pseudorandom-phase tomographic computer holography （DPP-TCH）. Color dispersion introduced by different wavelengths is well compensated by zero-padding operation in the red and green channels of object slices. Numerical reconstruction results show that the speckle noise and color-dispersion are well suppressed and that high-quality full-color holographic 3D imaging is feasible. The method is useful for improving the 3D image quality in holographic displays with pixelated phase-type spatial light modulators （SLMs）.

Advances in the light field displays based on integral imaging and holographic techniques(Invited Paper)

Light field displays comprise three-dimensional （3D） visual information presentation devices capable of providing realistic and full parallax autostereoscopic images. In this letter, the recent advances in the light field displays based on integral imaging （II） and holographic techniques are presented. Several advanced approaches to demonstrate the light field displays including viewing angle enhancement techniques of the II display, a fast hologram generation method using graphics processing unit （GPU） and multiple WRPs, and a holographic microscopy to display the living cells are reported. These methods improve some important constraints of the light field displays and add new features.

Review of Fresnel incoherent correlation holography with linear and non-linear correlations

Fresnel incoherent correlation holography(FINCH)is a well-established incoherent imaging technique.In FINCH,three selfinterference holograms are recorded with calculated phase differences between the two interfering,differently modulated object waves and projected into a complex hologram.The object is reconstructed without the twin image and bias terms by a numerical Fresnel back propagation of the complex hologram.A modified approach to implement FINCH by a single camera shot by pre-calibrating the system involving recording of the point spread function library and reconstruction by a nonlinear cross correlation has been introduced recently.The expression of the imaging characteristics from the modulation functions in original FINCH and the modified approach by pre-calibration in spatial and polarization multiplexing schemes are reviewed.The study reveals that a reconstructing function completely independent of the function of the phase mask is required for the faithful expression of the characteristics of the modulating function in image reconstruction.In the polarization multiplexing method by non-linear cross correlation,a partial expression was observed,while in the spatial multiplexing method by non-linear cross correlation,the imaging characteristics converged towards a uniform behavior.

Pixel super-resolution using wavelength scanning

Undersampling and pixelation affect a number of imaging systems, limiting the resolution of the acquired images, whichbecomes particularly significant for wide-field microscopy applications. Various super-resolution techniques have been implemented to mitigate this resolution loss by utilizing sub-pixel displacements in the imaging system, achieved, for example, byshifting the illumination source, the sensor array and/or the sample, followed by digital synthesis of a smaller effective pixel bymerging these sub-pixel-shifted low-resolution images. Herein, we introduce a new pixel super-resolution method that is basedon wavelength scanning and demonstrate that as an alternative to physical shifting/displacements, wavelength diversity can beused to boost the resolution of a wide-field imaging system and significantly increase its space-bandwidth product. We confirmedthe effectiveness of this new technique by improving the resolution of lens-free as well as lens-based microscopy systems anddeveloped an iterative algorithm to generate high-resolution reconstructions of a specimen using undersampled diffraction patterns recorded at a few wavelengths covering a narrow spectrum (10–30 nm). When combined with a synthetic-aperture-baseddiffraction imaging technique, this wavelength-scanning super-resolution approach can achieve a half-pitch resolution of250 nm, corresponding to a numerical aperture of ~ 1.0, across a large field of view (420 mm^(2)). We also demonstrated theeffectiveness of this approach by imaging various biological samples, including blood and Papanicolaou smears. Compared withdisplacement-based super-resolution techniques, wavelength scanning brings uniform resolution improvement in all directionsacross a sensor array and requires significantly fewer measurements. This technique would broadly benefit wide-field imagingapplications that demand larger space-bandwidth products.