arXiv subjects

Tobias Birnbaum

Publications and source records attributed to Tobias Birnbaum.

4 recordsLinked to original sources

arXiv2021

Optimization of phase-only holograms calculated with scaled diffraction calculation through deep neural networks

Computer-generated holograms (CGHs) are used in holographic three-dimensional (3D) displays and holographic projections. The quality of the reconstructed images using phase-only CGHs is degraded because the amplitude of the reconstructed image is difficult to control. Iterative optimization methods such as the Gerchberg-Saxton (GS) algorithm are one option for improving image quality. They optimize CGHs in an iterative fashion to obtain a higher image quality. However, such iterative computation is time consuming, and the improvement in image quality is often stagnant. Recently, deep learning-based hologram computation has been proposed. Deep neural networks directly infer CGHs from input image data. However, it is limited to reconstructing images that are the same size as the hologram. In this study, we use deep learning to optimize phase-only CGHs generated using scaled diffraction computations and the random phase-free method. By combining the random phase-free method with the scaled diffraction computation, it is possible to handle a zoomable reconstructed image larger than the hologram. In comparison to the GS algorithm, the proposed method optimizes both high quality and speed.

cs.CV↗

arXiv2020

Comprehensive Performance Analysis of Objective Quality Metrics for Digital Holography

Objective quality assessment of digital holograms has proven to be a challenging task. While prediction of perceptual quality of the recorded 3D content from the holographic wavefield is an open problem; perceptual quality assessment from content after rendering, requires a time-consuming rendering step and a multitude of possible viewports. In this research, we use 96 Fourier holograms of the recently released HoloDB database to evaluate the performance of well-known and state-of-the-art image quality metrics on digital holograms. We compare the reference holograms with their distorted versions: (i) before rendering on the real and imaginary parts of the quantized complex-wavefield, (ii) after converting Fourier to Fresnel holograms, (iii) after rendering, on the quantized amplitude of the reconstructed data, and (iv) after subsequently removing speckle noise using a Wiener filter. For every experimental track, the quality metric predictions are compared to the Mean Opinion Scores (MOS) gathered on a 2D screen, light field display and a holographic display. Additionally, a statistical analysis of the results and a discussion on the performance of the metrics are presented. The tests demonstrate that while for each test track a few quality metrics present a highly correlated performance compared to the multiple sets of available MOS, none of them demonstrates a consistently high-performance across all four test-tracks.

eess.IV↗

arXiv2019

Suitability Analysis of Holographic vs Light Field and 2D Displays for Subjective Quality Assessment of Fourier Holograms

Visual quality assessment of digital holograms is facing many challenges. Main difficulties are related to the limited spatial resolution and angular field of view of holographic displays in combination with the complexity of steering and operating them for such tasks. Alternatively, non-holographic displays - and in particular light-field displays - can be utilized to visualize the numerically reconstructed content of a digital hologram. However, their suitability as alternative for holographic displays has not been validated. In this research, we have investigated this issue via a set of comprehensive experiments. We used Fourier holographic principle to acquire a diverse set of holograms, which were either computer-generated from point clouds or optically recorded from real macroscopic objects. A final public data set comprising 96 holograms was created using three compression methods which encoded the holograms at four bit-depths. Three separate subjective-tests were conducted using a holographic display, a light field display and a 2D display. For these subjective experiments, a double stimulus, multi-perspective, multi-depth subjective testing methodology was designed and implemented. The tests show that the non-holographic displays indicate a higher sensitivity to artifacts than the holographic display, though at the same time it is demonstrated they are highly correlated. This indicates that the numerically reconstructed holograms rendered on a light field or 2D display have a high predictive value for the perceived quality on holographic display.

eess.IV↗

arXiv2017

Tolerant Compressed Sensing With Partially Coherent Sensing Matrices

Most of compressed sensing (CS) theory to date is focused on incoherent sensing, that is, columns from the sensing matrix are highly uncorrelated. However, sensing systems with naturally occurring correlations arise in many applications, such as signal detection, motion detection and radar. Moreover, in these applications it is often not necessary to know the support of the signal exactly, but instead small errors in the support and signal are tolerable. Despite the abundance of work utilizing incoherent sensing matrices, for this type of tolerant recovery we suggest that coherence is actually beneficial. We promote the use of coherent sampling when tolerant support recovery is acceptable, and demonstrate its advantages empirically. In addition, we provide a first step towards theoretical analysis by considering a specific reconstruction method for selected signal classes.

cs.IT↗