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14 pages, 5216 KiB

Open AccessArticle

A Sparse Capture Light-Field Coding Algorithm Based on Target Pixel Matching for a Multi-Projector-Type Light-Field Display System

by Qingyu Meng, Haiyang Yu, Xiaoyu Jiang and Xinzhu Sang

Photonics 2023, 10(2), 223; https://doi.org/10.3390/photonics10020223 - 19 Feb 2023

Cited by 2 | Viewed by 1291

Abstract

The traditional light-field coding algorithm used in a multi-projector-type light-field display system requires sophisticated and complex three-dimensional modeling processes or parallax images obtained through dense capture. Here we propose an algorithm based on target pixel matching, which directly uses parallax images without a [...] Read more.

The traditional light-field coding algorithm used in a multi-projector-type light-field display system requires sophisticated and complex three-dimensional modeling processes or parallax images obtained through dense capture. Here we propose an algorithm based on target pixel matching, which directly uses parallax images without a complex modeling process, and can achieve a more accurate light-field reconstruction effect under sparse capture conditions. For the lack of capture information caused by sparse capture, this algorithm compares the pixel similarity of the captured images of the same object point on different cameras to accurately determine the real capture information of the object point at different depths, which is recorded as the target pixel, and then the target pixel is encoded according to the lighting path to obtain the correct projector image array (PIA). By comparing the quality of PIAs generated by the traditional light-field coding algorithm and the display effect after loading the PIAs into the actual display system, we proved the effectiveness of the algorithm. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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17 pages, 3628 KiB

Open AccessArticle

Noise Considerations for Tomographic Reconstruction of Single-Projection Digital Holographic Interferometry-Based Radiation Dosimetry

by Tom Telford, Jackson Roberts, Alicia Moggré, Juergen Meyer and Steven Marsh

Photonics 2023, 10(2), 188; https://doi.org/10.3390/photonics10020188 - 09 Feb 2023

Cited by 1 | Viewed by 1363

Abstract

Optical Calorimetry (OC) is a 2D Digital Holographic Interferometry (DHI)-based measurement technique with potential applications for the 3D dosimetry of ultra-high dose rate (FLASH) radiation therapy beams through tomographic reconstruction. This application requires accurate measurements of DHI signals in environments with low signal-to-noise [...] Read more.

Optical Calorimetry (OC) is a 2D Digital Holographic Interferometry (DHI)-based measurement technique with potential applications for the 3D dosimetry of ultra-high dose rate (FLASH) radiation therapy beams through tomographic reconstruction. This application requires accurate measurements of DHI signals in environments with low signal-to-noise ratios (SNRs) in order to accurately measure absorbed energy to a medium per unit mass (Dose). However, tomographic reconstruction accuracy is sensitive to noise in the measurements. In this study, a virtual model of an OC dosimeter was used to characterize and model major sources of noise within a DHI setup, allowing for the modelled noise sources to be selectively reduced. The tomographic reconstruction of the 3D dose distribution was achieved using the inverse Abel transform. Reducing the noise contribution from atmospheric turbulence and mechanical vibration by one half improved the central axis reconstruction error from 6.5% to 1.3% and 1.1%, respectively, and the mean dose difference from 2.9% to 0.4% and 0.3%, respectively. This indicates the potential of the tomographic DHI-based 3D OC dosimeter to reconstruct accurate 3D dose distributions from a single projection if the specified sources of noise can be reduced to acceptable levels. The used methodology is applicable to any application of tomographic DHI where reconstruction quality is highly sensitive to noise. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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14 pages, 9926 KiB

Open AccessArticle

Enhancement of Imaging Quality of Interferenceless Coded Aperture Correlation Holography Based on Physics-Informed Deep Learning

by Rui Xiong, Xiangchao Zhang, Xinyang Ma, Lili Qi, Leheng Li and Xiangqian Jiang

Photonics 2022, 9(12), 967; https://doi.org/10.3390/photonics9120967 - 11 Dec 2022

Cited by 5 | Viewed by 1315

Abstract

Interferenceless coded aperture correlation holography (I-COACH) was recently introduced for recording incoherent holograms without two-wave interference. In I-COACH, the light radiated from an object is modulated by a pseudo-randomly-coded phase mask and recorded as a hologram by a digital camera without interfering with [...] Read more.

Interferenceless coded aperture correlation holography (I-COACH) was recently introduced for recording incoherent holograms without two-wave interference. In I-COACH, the light radiated from an object is modulated by a pseudo-randomly-coded phase mask and recorded as a hologram by a digital camera without interfering with any other beams. The image reconstruction is conducted by correlating the object hologram with the point spread hologram. However, the image reconstructed by the conventional correlation algorithm suffers from serious background noise, which leads to poor imaging quality. In this work, via an effective combination of the speckle correlation and neural network, we propose a high-quality reconstruction strategy based on physics-informed deep learning. Specifically, this method takes the autocorrelation of the speckle image as the input of the network, and switches from establishing a direct mapping between the object and the image into a mapping between the autocorrelations of the two. This method improves the interpretability of neural networks through prior physics knowledge, thereby remedying the data dependence and computational cost. In addition, once a final model is obtained, the image reconstruction can be completed by one camera exposure. Experimental results demonstrate that the background noise can be effectively suppressed, and the resolution of the reconstructed images can be enhanced by three times. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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11 pages, 996 KiB

Open AccessArticle

Circulating Tumor Cell Models Mimicking Metastasizing Cells In Vitro: Discrimination of Colorectal Cancer Cells and White Blood Cells Using Digital Holographic Cytometry

by Marek Feith, Yuecheng Zhang, Jenny L. Persson, Jan Balvan, Zahra El-Schich and Anette Gjörloff Wingren

Photonics 2022, 9(12), 955; https://doi.org/10.3390/photonics9120955 - 09 Dec 2022

Viewed by 1578

Abstract

Colorectal cancer (CRC) is the second most metastatic disease with the majority of cases detected in Western countries. Metastases are formed by circulating altered phenotype tumor cells causing 20% of CRC related deaths. Metastatic cells may show higher expression of surface molecules such [...] Read more.

Colorectal cancer (CRC) is the second most metastatic disease with the majority of cases detected in Western countries. Metastases are formed by circulating altered phenotype tumor cells causing 20% of CRC related deaths. Metastatic cells may show higher expression of surface molecules such as CD44, and changes in morphological properties are associated with increased invasiveness and poor prognosis. In this study, we intended to mimic the environment for metastasizing cells. Here, we used digital holographic cytometry (DHC) analysis to determine cellular morphological properties of three metastatic and two non-metastatic colorectal cancer cell lines to show differences in morphology between the CRC cells and peripheral blood mononuclear cells (PBMCs). By establishing differences in cell area, cell thickness, cell volume, and cell irregularity even when the CRC cells were in minority (5% out of PBMCs), DHC does discriminate between CRC cells and the PBMCs in vitro. We also analyzed the epithelial marker EpCAM and migration marker CD44 using flow cytometry and demonstrate that the CRC cell lines and PBMC cells differ in EpCAM and CD44 expression. Here, we present DHC as a new powerful tool in discriminating cells of different sizes in suspension together with a combination of biomarkers. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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13 pages, 6315 KiB

Open AccessArticle

Watermarking and Encryption for Holographic Communication

by Zehao He, Kexuan Liu and Liangcai Cao

Photonics 2022, 9(10), 675; https://doi.org/10.3390/photonics9100675 - 21 Sep 2022

Cited by 2 | Viewed by 1501

Abstract

Holographic communication is a three-dimensional (3D) video communication technology based on computer-generated holograms (CGHs) which has the potential to give users a more realistic visual perception. As this is an emerging field, the encrypted encoding and decoding methods in holographic communication have not [...] Read more.

Holographic communication is a three-dimensional (3D) video communication technology based on computer-generated holograms (CGHs) which has the potential to give users a more realistic visual perception. As this is an emerging field, the encrypted encoding and decoding methods in holographic communication have not been widely studied. In this work, a watermarking and encryption method for holographic communication is proposed. A watermark is inserted into the original image using the discrete cosine transform before the calculation of the CGH, while a secret key is employed to produce the encrypted CGH during the holographic calculation. Through the proposed watermarking and encryption method, the signal of holographic communication is difficult to decrypt. Even if the signal is decrypted, the source of the leak is easy to trace due to the existence of the watermark. The watermarking and encryption method can provide a practical solution for the privacy protection and copyright protection of 3D video communication. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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12 pages, 8156 KiB

Open AccessArticle

Deep Deconvolution of Object Information Modulated by a Refractive Lens Using Lucy-Richardson-Rosen Algorithm

by P. A. Praveen, Francis Gracy Arockiaraj, Shivasubramanian Gopinath, Daniel Smith, Tauno Kahro, Sandhra-Mirella Valdma, Andrei Bleahu, Soon Hock Ng, Andra Naresh Kumar Reddy, Tomas Katkus, Aravind Simon John Francis Rajeswary, Rashid A. Ganeev, Siim Pikker, Kaupo Kukli, Aile Tamm, Saulius Juodkazis and Vijayakumar Anand

Photonics 2022, 9(9), 625; https://doi.org/10.3390/photonics9090625 - 31 Aug 2022

Cited by 19 | Viewed by 2506

Abstract

A refractive lens is one of the simplest, most cost-effective and easily available imaging elements. Given a spatially incoherent illumination, a refractive lens can faithfully map every object point to an image point in the sensor plane, when the object and image distances [...] Read more.

A refractive lens is one of the simplest, most cost-effective and easily available imaging elements. Given a spatially incoherent illumination, a refractive lens can faithfully map every object point to an image point in the sensor plane, when the object and image distances satisfy the imaging conditions. However, static imaging is limited to the depth of focus, beyond which the point-to-point mapping can only be obtained by changing either the location of the lens, object or the imaging sensor. In this study, the depth of focus of a refractive lens in static mode has been expanded using a recently developed computational reconstruction method, Lucy-Richardson-Rosen algorithm (LRRA). The imaging process consists of three steps. In the first step, point spread functions (PSFs) were recorded along different depths and stored in the computer as PSF library. In the next step, the object intensity distribution was recorded. The LRRA was then applied to deconvolve the object information from the recorded intensity distributions during the final step. The results of LRRA were compared with two well-known reconstruction methods, namely the Lucy-Richardson algorithm and non-linear reconstruction. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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15 pages, 3677 KiB

Open AccessArticle

Speckle Noise Suppression Based on Empirical Mode Decomposition and Improved Anisotropic Diffusion Equation

by Xiaojiang Zhan, Chuli Gan, Yi Ding, Yi Hu, Bin Xu, Dingnan Deng, Shengbin Liao and Jiangtao Xi

Photonics 2022, 9(9), 611; https://doi.org/10.3390/photonics9090611 - 29 Aug 2022

Cited by 5 | Viewed by 1472

Abstract

Existing methods to eliminate the laser speckle noise in quantitative phase imaging always suffer from the loss of detailed phase information and the resolution reduction in the reproduced image. To overcome these problems, this paper proposes a speckle noise suppression method based on [...] Read more.

Existing methods to eliminate the laser speckle noise in quantitative phase imaging always suffer from the loss of detailed phase information and the resolution reduction in the reproduced image. To overcome these problems, this paper proposes a speckle noise suppression method based on empirical mode decomposition. Our proposed method requires only one image without additional equipment and avoids the complicated process of searching the optimal processing parameters. In this method, we use empirical mode decomposition to highlight the high frequency information of the interference image and use the Canny operator to perform edge detection, so the diffusion denoising process is guided by high-precision detection results to achieve better results. To validate the performance of our proposed method, the phase maps processed by our proposed method are compared with the phase maps processed by the improved anisotropic diffusion equation method with edge detection, the mean filter method and the median filter method. The experimental results show that the method proposed in this paper not only has a better denoising effect but also preserves more details and achieves higher phase reconstruction accuracy. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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Review

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28 pages, 8925 KiB

Open AccessReview

Fourier Transform Holography: A Lensless Imaging Technique, Its Principles and Applications

by Sara Mustafi and Tatiana Latychevskaia

Photonics 2023, 10(2), 153; https://doi.org/10.3390/photonics10020153 - 01 Feb 2023

Cited by 2 | Viewed by 6472

Abstract

Fourier transform holography (FTH) is a lensless imaging technique where the wave scattered by an object is superimposed with the wave scattered by a reference source positioned in the same plane. The distribution of the object is then reconstructed by simply calculating the [...] Read more.

Fourier transform holography (FTH) is a lensless imaging technique where the wave scattered by an object is superimposed with the wave scattered by a reference source positioned in the same plane. The distribution of the object is then reconstructed by simply calculating the Fourier transform of the recorded hologram. In this study, we outline the basic principles of FTH and provide an overview of the different types of references and the associated reconstruction algorithms. Current applications of FTH with different waves (light, electron, and X-ray) are presented, and their relationships with other coherent imaging techniques are discussed. Full article

(This article belongs to the Special Issue Advances and Application of Imaging on Digital Holography)

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