Measuring the shape (coordinates x, y, z ) and spectral characteristics (wavelength-dependent reflectance R (λ_i)) of macroscopic objects as a function of time (t) is of great interest in areas such as medical imaging, precision agriculture, or optical sorting. Here, we present an approach that allows to determine all these quantities with high resolution and accuracy, enabling measurement in five dimensions. We call this approach 5D hyperspectral imaging. We describe the design and implementation of a 5D sensor operating in the visible to near-infrared spectral range, which provides excellent spatial and spectral resolution, great depth accuracy, and high frame rates. The results of various experiments strongly indicate the great benefit of the new technology.

The contactless estimation of vital signs using conventional color cameras and ambient light can be affected by motion artifacts and changes in ambient light. On both these problems, a multimodal 3D imaging system with an irritation-free controlled illumination was developed in this work. In this system, real-time 3D imaging was combined with multispectral and thermal imaging. Based on 3D image data, an efficient method was developed for the compensation of head motions, and novel approaches based on the use of 3D regions of interest were proposed for the estimation of various vital signs from multispectral and thermal video data. The developed imaging system and algorithms were demonstrated with test subjects, delivering a proof-of-concept.

As the main concept, the Digital Twin (DT) shows its potential not only in industry 4.0 but also in other areas. One of the keys that decide the future of DT been known as its model technology. Through models can integrate features, behaviors, and properties of DT artifacts with efficiency, reusability, and interoperability, in order to build a complete mapping between the physical world and digital world, after that realize the ideal DT. This paper aims at comparing and analyzing the DT models in the scientific literature, retracing them from the initial one to the models in most recent researches. Thus, this study also emphasizes several principles of the DT model technology that is related to future work.

Vital signs, such as body temperature, heart rate, respiratory rate, and blood pressure are standard indicators of an individual’s physiological functions in most medical settings.¹ Monitoring these vital parameters is crucial for early diagnosis, medical treatment, risk assessment, and patient recovery monitoring.^2,3 With the advancement of medical measurement technology, oxygen saturation has increasingly become recognized as an indispensable fifth vital sign.⁴ Oxygen saturation indicates the percentage of oxygenated hemoglobin (${\mathrm{HbO}}_2$) and hemoglobin (Hb) in the blood, in which the artery should be in the range of 95% to 100% in healthy individuals.⁵ Many pulmonary diseases cause abnormalities in oxygen saturation values, such as acute pneumonia, chronic obstructive pulmonary disease (COPD), and sleep apnea syndrome (SAS). Furthermore, the outbreak of coronavirus (COVID-19) has further underscored the critical importance of oxygen saturation measurement.

High-speed 3-D imaging matches the increasing demands for real-time capability in nondestructive industrial inspection, human–machine interaction, biomedical and security applications, etc. The common real-time solutions for three-dimensional (3-D) imaging, e.g., passive stereo,^1,2 time-of-flight (ToF) cameras,^3,4 and focal tomography,⁵ are limited by their depth resolution and not suitable for tasks with high-accuracy requirements. A well-established high-accuracy 3-D imaging technique is the pattern projection-based stereo photogrammetry. It solves the stereo matching problem with the pixel-level virtual features created by the projection of a sequence of light patterns. So, the pattern projection method can realize the pixel matching even at a wide baseline, thus improving the depth resolution. Moreover, the virtual features ensure a high measurement robustness at nontextured or sparse-textured surfaces. For such 3-D imaging systems, there are two possible approaches to raise their 3-D frame rates. The first approach is to minimize the number $N$ of patterns for the computation of a single 3-D image, obviously $N=1$. The previous 3-D techniques based on single-frame pattern projection could be classified into two groups according to the pattern type: monochromatic patterns with phase modulation in the frequency domain⁶ 7. ^{– 8} and composite RGB fringe patterns, in which the phase shift is coded with RGB colors.⁹ 10. ^{– 11} However, the decoding of monochromatic patterns will confront a lot of artifacts at objects with shape discontinuities or very sharp edges, and a hard challenge at the RGB fringe projection is that the phase map unwrapping becomes difficult without additional patterns (e.g., gray codes). Moreover, these techniques are affected from nonuniform surface properties and thus are limited by their application occasions.

The fields of optical 3D measurement system applications are continuously expanding and becoming more and more diverse. To evaluate appropriate systems for various measurement tasks, comparable parameters are necessary, whereas the 3D modulation transfer function (3D-MTF) has been established as a further criterion. Its aim is the determination of the system response between the measurement of a straight, sharp-edged cube and its opposite ideal calculated one. Within the scope of this work simulations and practical investigations regarding the 3D-MTF’s influences and its main issues are specifically investigated. Therefore, different determined edge radii representing the high-frequency spectra lead to various decreasing 3D-MTF characteristics. Furthermore, rising sampling frequencies improve its maximum transfer value to a saturation point in dependence of the radius. To approve these results of previous simulations, three fringe projection scanners were selected to determine the diversity. As the best 3D-MTF characteristic, a saturated transfer value of H 3 D ( f N , 3 D ) = 0.79 has been identified at a sufficient sampling frequency, which is reached at four times the Nyquist limit. This high 3D resolution can mainly be achieved due to an improved camera projector interaction. Additionally, too small sampling ratios lead to uncertainties in the edge function determination, while higher ratios do not show major improvements. In conclusion, the 3D-MTF algorithm has thus been practically verified and its repeatability as well as its robustness have been confirmed.