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

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.

Image degradation characteristics and restoration based on regularization for diffractive imaging

In this paper, we focus on the 2D LUT (2-dimension look-up table) techniques for the mitigation of HPAs' (high power amplifiers') memory effects when transmitting WCDMA wideband signal. On the basis of the previous method, an improved two-dimensional LUT indexing method for HPA predistortion with memory is proposed. Simulation and experimental results show that the proposed method has more effective predistortion capabilities compared with the previous method.

Researchers have applied 3D Lookup Tables (LUTs) in cameras, offering new possibilities for enhancing image quality and achieving various tonal effects. However, these approaches often overlook the non-uniformity of color distribution in the original images, which limits the performance of learnable LUTs. To address this issue, we introduce a lightweight end-to-end image enhancement method called Simulated Infrared Fusion Guided Image-adaptive 3D Lookup Tables (SIRLUT). SIRLUT enhances the adaptability of 3D LUTs by reorganizing the color distribution of images through the integration of simulated infrared imagery. Specifically, SIRLUT consists of an efficient Simulated Infrared Fusion (SIF) module and a Simulated Infrared Guided (SIG) refinement module. The SIF module leverages a cross-modal channel attention mechanism to perceive global information and generate dynamic 3D LUTs, while the SIG refinement module blends simulated infrared images to match image consistency features from both structural and color aspects, achieving local feature fusion. Experimental results demonstrate that SIRLUT outperforms state-of-the-art methods on different tasks by up to 0.88 ~ 2.25dB while reducing the number of parameters. Code is available at https://github.com/riversky2025/SIRLUT.git .

In general, k lenses with different materials can achieve at most (k+1) color correction (k≥2). A superachromat containing three lenses is designed to achieve five-color correction in the 600-1600 nm waveband, where the maximum chromatic focal shift is controlled within 1/100,000 of the focal length, achieving an almost unprecedented result. Conditions for lens power combination of three thin lenses in contact are first derived based on the Buchdahl dispersion equation; then a metric is introduced to verify the five-color correction, and a correction method is proposed to improve the refractive index fitting accuracy of the Buchdahl model from ∼10-3 to ∼10-7. By traversing 197 ecofriendly glass materials in the CDGM glass library iteratively, 113 initial structures are obtained in only 61.75 s, from which the structure with the minimum chromatic focal shift is selected to be optimized with Opticstudio. By setting up required operands, the final structure being within the diffraction limit in a field of view of ±0.05∘ is obtained within only 6 s, where the maximum longitudinal chromatic aberration is close to the maximum chromatic focal shift. We provide a complete theoretical basis and important guidance for designing broadband superachromats with (k+2) color correction using only k lenses and the smallest chromatic focal shift, and based on the theories, we have developed a broadband interferometer.

In recent years, the demand for low-cost high-performance optical interconnect components has increased. One solution has been found with the development of the vertical cavity surface emitting laser (VCSEL) [1]. The VCSEL has a number of attractive characteristics for interconnects such as low operating voltage and current, low divergence circular beam, and the possibility of on-wafer testing and flip-chip mounting. While simple beam shaping can be accomplished using refractive optics, monolithically or in hybrid, more complex beam shaping such as combined beam splitting and focusing for optical fan-out can only be accomplished using diffractive optical elements (DOEs) [2]. Ideally, the DOE should be monolithically integrated with the VCSEL.

Snapshot Compressive Spectral Imaging Systems (SCSI) compress the scenes by capturing 2D projections of the encoded underlying signals. A decoder, trained with pre-acquired datasets, reconstructs the spectral images. SCSI systems based on diffractive optical elements (DOE) provide a small form factor and the single DOE can be optimized in an end-to-end manner. Since the spectral image is highly compressed in a SCSI system based on a single DOE, the quality of image reconstruction can be insufficient for diverse spectral imaging applications. This work proposes a multishot spectral imaging system employing a double-phase encoding with a double DOE architecture (DoDo), to improve the spectral reconstruction performance. The first DOE is fixed and provides the benefits of the diffractive optical systems. The second DOE provides the variable encoding of the multishot architectures. The work presents a differentiable mathematical model for the multishot DoDo system and optimizes the parameters of the DoDo architecture in an end-to-end manner. The proposed system was tested using simulations and a hardware prototype. To obtain a low-cost system, the implementation uses a deformable mirror for the variable DOE. The proposed DoDo system shows an improvement of up to 4dB in PSNR in the reconstructed spectral images compared with the single DOE system.

I present an optical system for the polar formatting of data in a spotlight-mode synthetic aperture radar. This system is implemented with only one diffractive optical element (DOE). Previously such a DOE could not be produced because the phase of the required transmission function of the DOE does not obey the continuity condition, which is a prerequisite for the conventional implementation of such optical transforms. Here I show how a DOE can be produced to perform the complete polar-formatting transform by incorporating branch-point phase singularities in the transmission function of the DOE. The computation of the transmission function is shown, and numerically computed diffraction patterns obtained from this DOE are also shown.

To address the loss of the ability to maintain zero-voltage switching (ZVS) in low-voltage, high-current four-switch buck-boost (FSBB) converters, this paper proposes an adaptive variable-frequency control strategy. From the perspective of extending the ZVS range, a frequency variation trajectory is proposed. Next, power inductor design principles are presented to address the filter design challenges arising from the wide operating frequency range. Finally, control variables are decoupled and DSP memory footprint is minimized through a 2D lookup table (LUT) combined with a PI feedback controller. Experimental validation on a 500 W FSBB converter prototype demonstrates full-load range ZVS maintenance at a 40 A output current with the peak efficiency reaching 98.528%.

Color space transformation using a 3D lookup table (LUT) with interpolation is used to correlate the source and destination color values in the lattice points of a 3D table, where nonlattice points are interpolated by using the nearest lattice points. This method has been used in many applications with quite satisfactory results, and incorporated into the ICC profile standard. In this chapter, the structure of the 3D-LUT approach is discussed and the mathematical formulations of interpolation methods are given. These methods are tested using several sets of data points. The similarities and differences of these interpolation methods are discussed.

This paper introduces a novel lensless full colour diffractive computational imaging system with a planar Multilevel Phase Mask (MPM) as a diffractive optical element (DOE). The novelty concerns: a methodology of MPM design for improved depth of focus (DoF); design of PSFs for RGB imaging and an inverse imaging algorithm with sparse colour image modelling simultaneous for all RGB channels. MPMs are step-wise invariant. The cubic wavefront coding (WFC) is incorporated in MPMs with optimization of number of levels and width of invariant steps. This design of MPM makes the system robust with respect to defocus (improves DoF) and diminish chromatic aberrations typical for DOEs. Broadband multichannel test-images are exploited for design and testing of the lensless system. We consider two alternative optical setups: Wavelength Multiplexing (WM) and Wavelength Division (WD). In WM, the light beam is broadband multichannel with light sources radiating all wavelengths simultaneously and a CMOS sensor is equipped with a Bayer colour filter array (CFA) for registration of spectral measurements. In this setup, a single MPM is designed for the broadband multichannel light beams. In WD, separate exposures of RGB channels are registered by a broadband grey-scale CCD sensor. Different MPMs are designed for each of the RGB channels. Simulation experiments demonstrate the essentially extended DoF of the designed lensless systems and the advanced accuracy and quality of imaging with respect to the corresponding WM and WD systems with refractive lenses. Due to robustness of the designed lensless system to chromatic aberrations, this advantage has a place even with respect to the lens-system.

In this paper, we propose a modeling equipment that obtains every equilibrium point of a magnetic levitation system automatically. To obtain every equilibrium point, we develop an automatic modeling equipment that measures the magnetic force exerted on the levitation object, the coil current of electromagnet, and the distance between the levitation object and the electromagnet. The modeling equipment is composed of two parts : the load cell equipment and the control board. The load cell equipment measures the magnetic force by a load cell and maintains certain position between the levitation object and electromagnet. The control board controls the voltage applied to the electromagnet and the position of load cell, and measures magnetic force, distance between the levitation object and electromagnet, and the coil current of electromagnet. An automatic algorithm for making a 2D lookup table from the experimentally measured data is proposed. Because a 2D lookup table reflects every equilibrium point, it is valid for various mass of levitation objects and the controller can be designed using the 2D lookup table without any further experiment.

In order to solve the problems of color distortion and blurring common in underwater images, this paper uses color channel compensation and grayscale equalization to correct color cast, and uses the total variation of the reweighted graph to estimate the fuzzy kernel to achieve image restoration. Based on the average gray value of the color channel, the color channel with serious information loss is compensated to reduce the deviation of the gray distribution between the color channels, and the gray distribution balance is further realized by segmented stretching. Combined with the reweighted graph total variation prior algorithm and the improved L-R unblinded restoration algorithm to restore the final image to remove blurring. Several sets of different data sets were selected to compare the proposed algorithm with several classical algorithms, and the evaluation results of subjective vision and three objective indicators were analyzed. The results show that the proposed algorithm can be applied to underwater image restoration, and the algorithm has good general applicability, which can effectively correct color cast, remove blur and improve image clarity.

The development of diffractive and refractive optics from ancient times (2000 years ago) to the present is traced from a theoretical and practical point of view. A comparative analysis of the possibilities of the two fields in optics is presented. The possibility for achromatization and corrections that exceed the boundary of diffractive and refractive optical elements is pointed out.

Diffractive and refractive optical elements have become an integral part of most high-resolution X-ray microscopes. However, they suffer from inherent chromatic aberration. This has to date restricted their use to narrow-bandwidth radiation, essentially limiting such high-resolution X-ray microscopes to high-brightness synchrotron sources. Similar to visible light optics, one way to tackle chromatic aberration is by combining a focusing and a defocusing optic with different dispersive powers. Here, we present the first successful experimental realisation of an X-ray achromat, consisting of a focusing diffractive Fresnel zone plate (FZP) and a defocusing refractive lens (RL). Using scanning transmission X-ray microscopy (STXM) and ptychography, we demonstrate sub-micrometre achromatic focusing over a wide energy range without any focal adjustment. This type of X-ray achromat will overcome previous limitations set by the chromatic aberration of diffractive and refractive optics and paves the way for new applications in spectroscopy and microscopy at broadband X-ray tube sources.