Image rendering of spatial light modulators (SLMs) is often degraded by various effects. Some efficient methods to get around nonuniformity, nonlinearity, and remanence and improve image rendering are presented. Optical laboratory results are presented for an analog ferroelectric liquid-crystal SLM using a high-speed camera. Focus is made on a preprocessing compensation method, using a spatial-dependant correction table. A high-speed "on-the-fly" implementation is also suggested.
KEYWORDS: Digital signal processing, Reconstruction algorithms, Optoelectronics, Computed tomography, Distortion, Signal to noise ratio, Prototyping, Electro optical modeling, Optical engineering, Surgery
This paper presents a hybrid processor dedicated to the reconstruction algorithm in multislice spiral computed tomography. The described architecture focuses on the advanced single-slice rebinning algorithm, which is a basic 2-D-to-3-D rebinning method developed in 2000. The hybrid processor is composed of four cores (rebinning, filtering, backprojection, and interpolation), including an optical processor for the backprojection. The system is modeled with a multi-abstraction-level approach. The model permits one to evaluate the dependence of both the reconstruction quality and the computation time with different parameters (reconstruction parameters, device features, etc.). It is used in a substantial simulation process allowing the identification of predominant degradation sources and the evaluation of their impact, and leading to the specification of each subsystem. A prototype of each core has been realized. The optical core has been identified as the most critical element, although results are very encouraging. This study has underlined that a computational speedup of more than two orders of magnitude could be reached. This is expected to be very useful for future challenging applications in the field of image-guided computer-assisted surgery, where the reconstruction rate would become critical to ensuring acceptable responsiveness.
Filtered backprojection (FBP) is the basic operation of image reconstruction algorithms in tomography. It is widely used but very time-consuming. We propose a new implementation, based on an optoelectronic architecture, providing a speedup of about two orders of magnitude over a classical digital implementation. The realization of the optical core, based on a rotated Dove prism, requires careful attention in order to ensure good image quality. This aspect has been studied in simulation with a suitable model of the architecture, and in practice with an experimental setup. Results are very encouraging.
Most of the present high-speed light modulator technologies perform only binary modulation, which is not sufficient for visualization applications. A greyscale images could be obtained using temporal accumulation of binary images. This technique, known as temporal multiplexing, is applied without difficulties in applications with incoherent light (e.g. DMD video projectors). In coherent application, where the phase of the light is to take into account, temporal decomposition could introduce errors. In this paper, this point will be studied theoretically and with simulations on an optical image processor.
A VHDL-AMS model of a surface-stabilized ferroelectric liquid crystal cell is presented in this paper. The model is based on the uniform FLC theory known since 1990. Although not quantitative, this approach gives us a good idea of the behaviour of such crystals. The model will be characterized and the results will be compared. Many related phenomena (effect of the temperature, ion transport...) will be introduced to complete the behavioural description. The purpose of this work is the design of virtual prototype for a high-speed spatial light modulator.