2D Lookup Table Research Articles

NILUT: Conditional Neural Implicit 3D Lookup Tables for Image Enhancement

3D lookup tables (3D LUTs) are a key component for image enhancement. Modern image signal processors (ISPs) have dedicated support for these as part of the camera rendering pipeline. Cameras typically provide multiple options for picture styles, where each style is usually obtained by applying a unique handcrafted 3D LUT. Current approaches for learning and applying 3D LUTs are notably fast, yet not so memory-efficient, as storing multiple 3D LUTs is required. For this reason and other implementation limitations, their use on mobile devices is less popular. In this work, we propose a Neural Implicit LUT (NILUT), an implicitly defined continuous 3D color transformation parameterized by a neural network. We show that NILUTs are capable of accurately emulating real 3D LUTs. Moreover, a NILUT can be extended to incorporate multiple styles into a single network with the ability to blend styles implicitly. Our novel approach is memory-efficient, controllable and can complement previous methods, including learned ISPs. Code at https://github.com/mv-lab/nilut

AdvLUT: Cloaking Geographic Location With Semantic-Based Adversarial 3D LookUp Tables

AdvLUT: Cloaking Geographic Location With Semantic-Based Adversarial 3D LookUp Tables

Dynamic Dead-Time Compensation Method Based on Switching Characteristics of the MOSFET for PMSM Drive System

In order to effectively avoid the shoot-through issue of the semiconductor device (such as the power metal-oxide-semiconductor field-effect transistor (MOSFET)) adopted in the phase leg of the motor drives, a dead-time zone should be inserted. However, the nonlinearity caused by the dead-time effect will bring about voltage/current distortion, as well as high-order harmonics, which largely degrades the performance of motor drives, especially in low-speed operations with slight loads. In this paper, a dead-time compensation method is proposed to suppress such side effects caused by dead-time zones and improve the performance of motor drives. Compared with other existing methods, the proposed method is mainly focused on the switching characteristics of the power MOSFET, which is directly relative to the compensation time in each pulse-width modulation (PWM) period. Firstly, a detailed derivation process is elaborated to reveal the relationship between compensation time and the switching performance of the MOSFET. Meanwhile, the switching process of the MOSFET is also well analyzed, which summarizes the variations in the switching time of the MOSFET with a varied load current. Then, the multipulse test (MPT) is carried out to obtain accurate values of the switching time with the varied load current in a wide range (0–80 A) and form a 2D lookup table. As a result, the compensation method can easily be realized by combining the lookup table and linear interpolation based on the phase current of the motor dynamically. Finally, the effectiveness of the proposed method is verified based on a 12 V permanent magnet synchronous machine (PMSM) drive system. According to the relative experiment results, it can be clearly observed that the time-domain waveform distortion, high-order harmonics, and total harmonic distortion (THD) value are reduced significantly with the proposed dynamic compensation method.

Model-based nonlinear dynamic optimisation for the optimal flow rate of vanadium redox flow batteries

The control of the electrolyte flow rate is crucial to ensure the efficient operation of a vanadium redox flow battery (VRFB) system. In this paper, a model-based nonlinear dynamic optimisation (MNDO) method is proposed and implemented in MATLAB/Simulink to study the optimal flow rate under constant current (CC) and constant current–constant voltage (CC–CV) charging methods for a VRFB. A 5 kW/3 kWh VRFB system is considered to investigate the feasibility and accuracy of the established model. System efficiency is the optimisation objective in this study, where all case studies are carried out within 15% to 85% state of charge (SOC). The simulation results show that the proposed method enhanced battery performance by improving the overall VRFB system efficiency under different charging methods. Furthermore, the simulation results show that the CC–CV method is more energy-efficient than the CC method but requires more charging time. An in-depth analysis is carried out to discuss the underlying merits of the proposed method in balancing the losses caused by the concentration overpotential and pump energy consumption in a varying power environment. Moreover, further analyses are carried out to highlight the merits of the CC–CV charging method in saving energy while charging and reducing system imbalance. Finally, a 2D lookup table is designed based on the results from the proposed MNDO method that offers a practical controller of the electrolyte flow rate without requiring excessive computational resources. The performance of the 2D lookup table has been evaluated within 100 charging/discharging cycles. It achieves a system efficiency gain of up to 1.48% under CC–CV charging operation compared with the CC charging method and optimal conventional flow rate control method.

A Constant Frequency ZVS Modulation Scheme for Four-Switch Buck–Boost Converter With Wide Input and Output Voltage Ranges and Reduced Inductor Current

The pseudo continuous current mode (PCCM) four-switch buck-boost (FSBB) converter with negative valley inductor current is suitable for applications where zero-voltage-switching (ZVS) and voltage step-up and step-down are required. To improve its efficiency, many ZVS modulation schemes have been proposed to minimize the root mean square (RMS) inductor current. However, when both input and output voltage ranges are wide, the three-dimensional (3D) look-up table (LUT) with huge data quantity or the switching frequency with wide variation range is typically required in previous schemes. In this paper, a ZVS modulation scheme with constant switching frequency and simple real-time calculation is proposed. Only with a 2D LUT in a small range of input and output voltage, RMS inductor current can be minimized. Moreover, the switching frequency is constant with the proposed scheme. In addition, ZVS conditions, which are accurate and simple, are derived to facilitate the minimization of RMS inductor current. A 1500W FSBB prototype with input and output voltage ranges of 200-400V is built to verify the proposed modulation scheme and derived ZVS conditions.

High-efficiency and high-fidelity optical signal transmission in free space through scattering media using 2D random amplitude-only patterns and look-up table

A new approach using 2D random amplitude-only patterns and look-up table (LUT) is proposed to realize high-efficiency and high-fidelity optical signal transmission in free space through scattering media. Any digital signal only containing 0 and 1 can be optically transmitted with high fidelity in free space through scattering media using only 4 pre-generated 2D random amplitude-only patterns stored in a database. Any grayscale image with values ranging from 0 to 255 can also be transmitted with high fidelity in a direct mode using only 512 pre-generated 2D random amplitude-only patterns stored in a database. For analog signals, a LUT can also be constructed to facilitate optical signal transmission in free space through scattering media. Optical experiments are carried out to verify feasibility and effectiveness of the proposed method. The proposed method can provide a novel insight for high-efficiency and high-fidelity optical signal transmission in free space through scattering media.

Modeling and Evaluation of Mutual Coupling Effect in Conventional Switched Reluctance Machines Using Space Vector Representation

This paper presents a non-linear model for conventional switched reluctance machines (CSRMs) that considers the mutual coupling between phases. Although CSRMs are based on single-phase excitation, there is usually an overlapping between the excited phases. During this overlapping, the CSRM is at 2-phase excitation and the single-phase representation of motor dynamics is not accurate. Hence, a dynamic model is presented in this paper that that accounts for the the mutual coupling between phases in addition to the effects of saturation and spatial harmonics. The proposed method is based on modeling the resultant current vector due to 2-phase excitation in space. The relationship between the resultant current and flux linkage vectors is obtained at different rotor positions using finite element method (FEM). This relationship is saved as a 3D lookup table (LUT). These 3D LUTs are reduced into 2D LUTs independent of rotor position by representing the phase currents as vectors instead of instantaneous values. Similarly, the relationship between the resultant current vector and the electromagnetic torque is obtained and saved as a 3D lookup table. The proposed method is compared with a conventional model where the mutual coupling is not considered. This comparison is conducted using FEM on two different motors; the first motor is 12/8 3-phase 2kW CSRM and the second motor is 24/16 3-phase 75kW CSRM. FEM results show that the mutual coupling is significant for high power motors. The proposed dynamic model is compared with experimental results using the 12/8 3-phase 2kW CSRM.

Improved CYGNSS Wind Speed Retrieval Using Significant Wave Height Correction

This article presents the methodology for an improved estimation of the sea surface wind speed measured by the cyclone global navigation satellite system (CYGNSS) constellation of satellites using significant wave height (SWH) information as external reference data. The methodology consists of a correcting 2D look-up table (LUT) with inputs: (1) the CYGNSS wind speed given by the geophysical model function (GMF); and (2) the collocated reference SWH given by the WW3 model, which is forced by winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) organization. In particular, the analyzed CYGNSS wind speeds are the fully developed seas (FDS) obtained with the GMF 3.0, and the forcing winds are the ECMWF forecast winds. Results show an increase in sensitivity to large winds speeds and an overall reduction in the root mean square difference (RMSD) with respect to the ECMWF winds from 2.05 m/s to 1.74 m/s. The possible influence of the ECWMF winds on the corrected winds (due to their use in the WW3 model) is analyzed by considering the correlation between: (1) the difference between the ECMWF winds and those from another reference; and (2) the difference between the corrected CYGNSS winds and those from the same reference. Results using ASCAT, WindSat, Jason, and AltiKa as references show no significant influence.

Dynamic Vector Modeling of Three-Phase Mutually Coupled Switched Reluctance Machines with Single dq-Quadrant Look-up Tables

This paper presents a dynamic modeling method for a 3-phase mutually coupled switched reluctance machine (MCSRM) considering spatial harmonics, and saturation. The conventional modeling methods of MCSRMs are based on 3D look-up tables (LUTs), where the phase flux linkages are considered as state variables. These 3D LUTs describe the phase currents with respect to phase flux linkages, and rotor position. The 3D LUTs represent two $dq$ quadrants, and are obtained from finite element analysis (FEA) by multi-phase excitation where the excitation currents cover two quadrants in the $dq$ synchronous reference frame. The LUTs used in the proposed method represent the phase current, and electro-magnetic torque as vectors. The magnitude, and the angle of these vectors are represented by the sine, and cosine Fourier coefficients. Hence, rotor position is not an input to the LUTs, and the proposed method uses 2D LUTs. Additionally, the flux linkages in the four $dq$ quadrants possess symmetry for MCSRMs. Therefore, LUTs corresponding to only one $dq$ quadrant are required. The single-quadrant based LUTs reduces the number of FEA steps, and the size of the LUTs by 50% compared to the two-quadrant LUT based models. Finally, the proposed method is validated using FEA, and experiments for a 12/8 MCSRM.

Learning Image-Adaptive 3D Lookup Tables for High Performance Photo Enhancement in Real-Time.

Recent years have witnessed the increasing popularity of learning based methods to enhance the color and tone of photos. However, many existing photo enhancement methods either deliver unsatisfactory results or consume too much computational and memory resources, hindering their application to high-resolution images (usually with more than 12 megapixels) in practice. In this paper, we learn image-adaptive 3-dimensional lookup tables (3D LUTs) to achieve fast and robust photo enhancement. 3D LUTs are widely used for manipulating color and tone of photos, but they are usually manually tuned and fixed in camera imaging pipeline or photo editing tools. We, for the first time to our best knowledge, propose to learn 3D LUTs from annotated data using pairwise or unpaired learning. More importantly, our learned 3D LUT is image-adaptive for flexible photo enhancement. We learn multiple basis 3D LUTs and a small convolutional neural network (CNN) simultaneously in an end-to-end manner. The small CNN works on the down-sampled version of the input image to predict content-dependent weights to fuse the multiple basis 3D LUTs into an image-adaptive one, which is employed to transform the color and tone of source images efficiently. Our model contains less than 600K parameters and takes less than 2 ms to process an image of 4K resolution using one Titan RTX GPU. While being highly efficient, our model also outperforms the state-of-the-art photo enhancement methods by a large margin in terms of PSNR, SSIM and a color difference metric on two publically available benchmark datasets. Code will be released at https://github.com/HuiZeng/Image-Adaptive-3DLUT.

Strawberry ripeness calibrated 2D colour lookup table for field-deployable computer vision

Efficient strawberry harvesting using semi-autonomous robotic pickers requires a method for fast, automatic discrimination between ripe and unripe berries. In this paper we present a strawberry ripeness algorithm that has been developed and tested on images obtained with commercial cameras, recorded under daylight illumination on an outdoor strawberry farm. The method uses a 2D lookup table seeded such that regions for ripe strawberry, unripe strawberry and strawberry calyx exist in distinct locations in the table. Measurements show the ratio of ripe to unripe area provides a good estimator of ripeness and that the approach was practical for further extension to real-time use.

Identification of look-up tables using gradient algorithm

In view of the relatively low computational load, look-up tables (or maps) are usually used to approximate nonlinear function or characterize operating-point-dependent system variables in typical embedded applications. Aiming at the problem of off-line identifying the look-up tables, a method based on the gradient algorithm is presented to estimate the look-up table parameters in this paper. The nonlinear function is approximated in terms of the piecewise linear interpolation model with the look-up table parameters, which can be rewritten as a dot product between the regression vector and unknown parameter vector using membership function. With the approximation error of the nonlinear function, a method for updating look-up tables using the gradient algorithm is given, and the relationship between the parameter estimation error and model approximation error is explicitly derived. To guarantee the convergence of the look-up table parameters estimation, a condition for the persistent excitation of the look-up table input is derived, which also provides a theoretical basis for the data characteristics of the look-up table input required to identify look-up table parameters offline using dynamic data. The validity of the proposed method is verified respectively by updating a one-dimensional (1D) look-up table, and the identification of the two-dimensional (2D) look-up table for the throttle discharge coefficient of a spark ignition gasoline engine form engine simulation tool enDYNA.

A fast iron loss calculation model for switched reluctance motors

A fast method to calculate the iron loss of switched reluctance motor (SRM) is proposed. The key of the method is that the flux density waveforms in different parts of the motor can be obtained quickly. First, the static flux density data varying with phase current and rotor position in various parts of SRM are obtained by finite element method (FEM). Then, the static flux density data are stored in 2D look-up tables in Matlab/Simulink to get the flux density waveforms by look-up table method, and the obtained flux density waveforms are verified by FEM results. Since the flux waveforms are non-sinusoidal and non-linear, an accurate and fast model for the iron loss prediction is presented, and different modified factors are applied to calculate the hysteresis loss according to the classification of flux density waveforms. Based on that, the calculation model is established in Matlab/Simulink, and iron losses of a three-phase 6/4 structure SRM under different turn-on and turn-off angles and load conditions are calculated and analysed. Finally, measured results are presented to verify the precision of the calculation model.

Color correction with 3D lookup tables in diffractive optical imaging systems

Diffractive optical elements (DOE) have significant advantage over refractive optics in linear dimensions and weight. However, the quality of images produced by a diffractive optics-based system suffers from strong distortions. In previous papers, we introduced and enhanced post-capture computational image reconstruction for diffractive Fresnel lens. In this paper, we revise chromatic shift correction method. Energy redistribution between diffractive orders results in chromatic shift and affects image quality. Each of the RGB channels has nonlinear flare spots from two other channels. In this paper, we present multicomponent color correction using three-dimensional lookup tables that takes into account the nonlinear relationship between color channels. PSNR values are used to compare the quality of the presented multicomponent approach with a previously described single-channel method.

Prototype of 6-DOF Magnetically Levitated Stage Based on Single Axis Lorentz force Actuator

We present a prototype of 6-DOF magnetically levitated stage based on single axis Lorentz force actuator is capable of positioning down to micron in several millimeter travel range with a simple and compact structure. The implementation of the Lorentz force actuators, instrument modeling, and motion controller of the maglev system are described. With the force-gap relationship of the actuator solved by Gaussian quadrature, 2-demsional (2D) lookup table is employed to store the result for the designing of control system. Based on the force-gap relationship, we choose the suitable stroke of each actuator to develop the stability of the maglev stage. Complete decoupling matrix is analyzed here to establish a decoupled dynamics between resulting six axis motion and eight outputs to the actuators. The design travel volume of the stage is 2mm×2mm×2mm in translation and 80mrad×80mrad×40mrad in rotation. With a constant gain and critical damping PID controller, the resolution of the translation is 2.8um and 4um root mean square in horizontal and vertical direction respectively. Experimental results are presented to illustrate the positioning fluctuations, step responds and multi axis motion. Some comparative tests are taken to highlight the advantage resulted from the accurate force-gap relationship, suitable stroke, and complete decoupling matrix.

Developing Calibrating Curves for a Trilinear Interpolation Model During Display Characterization

Trilinear interpolation is a method of multivariate interpolation on a three-dimensional regular grid. It approximates the value of an intermediate point using data on the lattice points, and thus is frequently used for display characterization with 3D lookup tables (3D LUTs). However, large color errors are usually caused by the nonlinear relationship between the source RGB space and the destination CIELAB space. In this article the display characterization is improved by modifying the traditional trilinear interpolation model. First, the Yule–Nielsen n-factor is applied to the destination functions, for the purpose of reducing the nonlinearity between the source and destination color spaces. Afterward, different calibrating curves are developed to calculate the effective values of the source RGB values. The input/source RGB values are usually called nominal values, and the effective values can be regarded as the optimized RGB values which improve the matching degree of the predicted and measured destination CIELAB values. In experiment, a Toshiba M5 liquid crystal display is characterized by using the modified trilinear interpolation model, and the forward and inverse characterization errors of different methods are calculated and compared. The evaluation results demonstrate that both the average and the maximum color errors have significantly decreased when calibrating curve III (one of the three types of curves developed) is employed in combination with the optimal n-factor. Thus, the method of developing effective calibrating curves and finding optimal n-factors proposed in this article can be adopted during display characterization. © 2016 Society for Imaging Science and Technology.

Developing Calibrating Curves for a Trilinear Interpolation Model During Display Characterization

Trilinear interpolation is a method of multivariate interpolation on a three-dimensional regular grid. It approximates the value of an intermediate point using data on the lattice points, and thus is frequently used for display characterization with 3D lookup tables (3D LUTs). However, large color errors are usually caused by the nonlinear relationship between the source RGB space and the destination CIELAB space. In this article the display characterization is improved by modifying the traditional trilinear interpolation model. First, the Yule‐Nielsen n-factor is applied to the destination functions, for the purpose of reducing the nonlinearity between the source and destination color spaces. Afterward, different calibrating curves are developed to calculate the effective values of the source RGB values. The input/source RGB values are usually called nominal values, and the effective values can be regarded as the optimized RGB values which improve the matching degree of the predicted and measured destination CIELAB values. In experiment, a Toshiba M5 liquid crystal display is characterized by using the modified trilinear interpolation model, and the forward and inverse characterization errors of different methods are calculated and compared. The evaluation results demonstrate that both the average and the maximum color errors have significantly decreased when calibrating curve III (one of the three types of curves developed) is employed in combination with the optimal n-factor. Thus, the method of developing effective calibrating curves and finding optimal n-factors proposed in this article can be adopted during display characterization.

Electromagnetic modeling and control of switched reluctance motor using finite elements

This paper considered the implementation of a current control method for switched reluctance motors (SRMs) and presented a novel approach to the accurate online modeling of a three phase 6/4 SRM drive. A three phase 6/4 SRM is given theoretical calculation of inductance of the SRM model. The SRM was then tested in a Matlab/Simulink environment and numerically analyzed by using nonlinear 2D look-up tables created from its calculated flux linkage and static torque data. The simulation studied the hysteresis and voltage control strategies. The ideal waveform of stator current under the voltage-current condition and improved shape of rotor were proposed.

Synchronized 2D/3D optical mapping for interactive exploration and real-time visualization of multi-function neurological images

Efficient software with the ability to display multiple neurological image datasets simultaneously with full real-time interactivity is critical for brain disease diagnosis and image-guided planning. In this paper, we describe the creation and function of a new comprehensive software platform that integrates novel algorithms and functions for multiple medical image visualization, processing, and manipulation. We implement an opacity-adjustment algorithm to build 2D lookup tables for multiple slice image display and fusion, which achieves a better visual result than those of using VTK-based methods. We also develop a new real-time 2D and 3D data synchronization scheme for multi-function MR volume and slice image optical mapping and rendering simultaneously through using the same adjustment operation. All these methodologies are integrated into our software framework to provide users with an efficient tool for flexibly, intuitively, and rapidly exploring and analyzing the functional and anatomical MR neurological data. Finally, we validate our new techniques and software platform with visual analysis and task-specific user studies.

Modelling Electromagnetic Suspension Force Using Measured Inductance-Airgap Data

Electromagnetic suspension system is commonly used in the field of high-speed vehicle, conveyor system, tool machines and frictionless bearing. Modelling a magnetic system requires modelling the magnetic force characteristics to- gether with the current and the position. In this work; a 1D look-up table, of measured data, was used to represent the in- ductance as a function of the airgap. A 2D look-up table was generated to represent the electromagnetic force as a function of the current and the airgap. The proposed model account for both inductance variation and current variation as the airgap is changing.