The objective of this investigation was to develop and investigate methods for point cloud generation by image matching using aerial image data collected by quadrocopter type micro unmanned aerial ...vehicle (UAV) imaging systems. Automatic generation of high-quality, dense point clouds from digital images by image matching is a recent, cutting-edge step forward in digital photogrammetric technology. The major components of the system for point cloud generation are a UAV imaging system, an image data collection process using high image overlaps, and post-processing with image orientation and point cloud generation. Two post-processing approaches were developed: one of the methods is based on Bae Systems' SOCET SET classical commercial photogrammetric software and another is built using Microsoft(®)'s Photosynth™ service available in the Internet. Empirical testing was carried out in two test areas. Photosynth processing showed that it is possible to orient the images and generate point clouds fully automatically without any a priori orientation information or interactive work. The photogrammetric processing line provided dense and accurate point clouds that followed the theoretical principles of photogrammetry, but also some artifacts were detected. The point clouds from the Photosynth processing were sparser and noisier, which is to a large extent due to the fact that the method is not optimized for dense point cloud generation. Careful photogrammetric processing with self-calibration is required to achieve the highest accuracy. Our results demonstrate the high performance potential of the approach and that with rigorous processing it is possible to reach results that are consistent with theory. We also point out several further research topics. Based on theoretical and empirical results, we give recommendations for properties of imaging sensor, data collection and processing of UAV image data to ensure accurate point cloud generation.
Automated count of Nile Red fluorescent microplastics allows fast and reliable quantification. However, factors involving staining, digital camera conditions and settings introduce variability to the ...results. The objective of this paper is to identify and propose solutions to these factors and improve on the previous MP-VAT script. While removal of digital sensor defects had little influence on results and staining can be reduced to 5 min, Nile Red concentrations cannot be reduced <0.01 mg mL−1, the 470 nm LED lantern emission must be >1600 lx, and photographic conditions should be maintained as stable as possible ideally improving the filter membrane area and using the recommended settings of 2 s, ISO100, F5.6. It was also found that Nile Red can be removed from microplastics using acetone or hydrogen peroxide with iron. More importantly, both particles and fluorescent are lost with time and thus quantification should be conducted within a week. Finally, MP-VAT 2.0 was developed to remove unselected areas and to identify only red particles, excluding white reflections from quantification. This updated version of MP-VAT produced improved recovery rates of 98.2 ± 6.9 for spiked samples and 95.9 ± 10.3 on actual environmental samples, presenting a cheap and reliable complementary method for microplastic identification.
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•Stable conditions are needed for proper quantification of fluorescent microplastics.•Staining with 0.01 mg mL−1 of Nile Red under 5 min produced good fluorescence.•Camera should be set to 2 s, ISO100, F5.6 and focused to maximize sample area.•Light emission from the 470 nm LED lantern should be >1600 lx.•Improved MP-VAT 2.0 presents recovery rates of 95.9 ± 10 in environmental samples.
Effective measurement and management of soil organic carbon (SOC) are essential for ecosystem function and food production. SOC has an important influence on soil properties and soil quality. ...Conventional SOC analysis is expensive and time-consuming. The development of spectral imaging sensors enables the acquisition of larger amounts of data using cheaper and faster methods. In addition, satellite remote sensing offers the potential to perform surveys more frequently and over larger areas. This research aimed to measure SOC content with colour as an indirect proxy. The measurements of soil colour were made at an agricultural site of the Czech Republic with an inexpensive digital camera and the Sentinel-2 remote sensor. Various soil colour spaces and colour indices derived from the (i) reflectance spectroscopy in the selected wavelengths of the visible (VIS) range (400–700 nm), (ii) RGB digital camera, and (iii) Sentinel-2 visible bands were used to train models for prediction of SOC. For modelling, we used the machine learning method, random forest (RF), and the models were validated with repeated 5-fold cross-validation. For prediction of SOC, the digital camera produced R2 = 0.85 and RMSEp = 0.11%, which had higher R2 and similar RMSEp compared to those obtained from the spectroscopy (R2 = 0.78 and RMSEp = 0.09%). Sentinel-2 predicted SOC with lower accuracy than other techniques; however, the results were still fair (R2 = 0.67 and RMSEp = 0.12%) and comparable with other methods. Using a digital camera with simple colour features was efficient. It enabled cheaper and accurate predictions of SOC compared to spectroscopic measurement and Sentinel-2 data.
•Various colour spaces and indices were used to model SOC.•Potential of RGB camera and S2 to assess SOC were compared to reflectance spectroscopy.•Applying colour indices was preferable to using simple colour spaces.•Digital camera is a promising tool for fast and cheap estimation of SOC.
STUDY OF DIGITAL CAMERA CALIBRATION ON A FLAT TEST OBJECT Govorov, A. V.; Chibunichev, A. G.; Makarov, S. B.
International archives of the photogrammetry, remote sensing and spatial information sciences.,
08/2020, Letnik:
XLIII-B2-2020
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
The paper presents a method for calibration of digital cameras based on the use of a flat test object. The main distinctive feature of this method is that the camera is fixed and does not change its ...position in space. A series of images of a flat test object (for example, a chessboard) is taken at various distances and inclination of the test object. One should tilt the test object relative to the image plane in order to avoid ambiguity in solving the problem. All these images are measured separately, and processing is performed together, counting them as one image with common exterior orientation elements. Experimental studies have shown sufficient efficiency of such calibration, which is easily implemented and gives positive results in comparison with the classical calibration of the camera on a spatial test object. The results of experimental studies on real images have shown that proposed calibration method gives the comparable with conventional method accuracy. Thus, it is possible to use simple and cheap flat calibration test object instead of spatial one. To achieve the maximum result in camera calibration accuracy, use this method to tilt the chessboard at angles in the range of 30–40 degrees to the optical axis of the camera being calibrated.
The development of full-field, accurate vibration testing techniques has been vastly valued by the academic and engineering community. However, due to the limited data transmission speed of digital ...cameras, the contradiction between speed and resolution remains in the traditional full-field vibration measurement systems based on image measurement, failing to acquire high-resolution images at high-speed simultaneously. In this paper, a high-speed and high-resolution full-field vibration displacement measurement system is established based on the grid CCD moiré method. A periodic grid is arranged on the surface of the sample as a deformation carrier, and the periodic pixel of the digital camera is used as a reference grating that ‘enlarges’ the grid on the surface of the sample to form a grid CCD moiré with a geometry significantly larger than the original, capturing images for deformation analysis. This approach lowers the requirement of digital image resolution for high-resolution deformation measurement, reducing the contradiction between speed and resolution in full-field vibration measurement. In this paper, the principle and implementation of full-field vibration measurement using the CCD moiré method are introduced, and the experiment results of full-field in-plane vibration displacement measurement are included, verifying the effectiveness and reliability of the system.
•A full-field vibration displacement measurement system is established based on CCD moiré method.•A series of experiments are used to verify the measurement accuracy and advantages of the grid CCD moiré method.•An experimental study of in-plane full-field vibration displacement measurement based on the CCD moiré method is conducted.
•An UAV was used for multi-temporal quantification of vegetation fraction.•Overall classification accuracy up to 92% were achieved with visible vegetation.•The excess green index reported the best ...result for vegetation mapping with UAV imagery.•Flight altitude scarcely affected classification accuracy.•UAV imagery is suitable for analysis of narrow row crops as wheat.
Mapping vegetation in crop fields is an important step in remote sensing applications for precision agriculture. Traditional aerial platforms such as planes and satellites are not suitable for these applications due to their low spatial and temporal resolutions. In this article, a UAV equipped with a commercial camera (visible spectrum) was used for ultra-high resolution image acquisition over a wheat field in the early-season period. From these images, six visible spectral indices (CIVE, ExG, ExGR, Woebbecke Index, NGRDI, VEG) and two combinations of these indices were calculated and evaluated for vegetation fraction mapping, to study the influence of flight altitude (30 and 60m) and days after sowing (DAS) from 35 to 75 DAS on the classification accuracy. The ExG and VEG indices achieved the best accuracy in the vegetation fraction mapping, with values ranging from 87.73% to 91.99% at a 30m flight altitude and from 83.74% to 87.82% at a 60m flight altitude. These indices were also spatially and temporally consistent, allowing accurate vegetation mapping over the entire wheat field at any date. This provides evidence that visible spectral indices derived from images acquired using a low-cost camera onboard a UAV flying at low altitudes are a suitable tool to use to discriminate vegetation in wheat fields in the early season. This opens the doors for the utilisation of this technology in precision agriculture applications such as early site specific weed management in which accurate vegetation fraction mapping is essential for crop-weed classification.
Cataract is one of the major causes of blindness in the world. Its early detection and treatment could greatly reduce the risk of deterioration and blindness. Instruments commonly used to detect ...cataracts are slit lamps and fundus cameras, which are highly expensive and require domain knowledge. Thus, the problem is that the lack of professional ophthalmologists could result in the delay of cataract detection, where medical treatment is inevitable. Therefore, this study aimed to design a convolutional neural network (CNN) with digital camera images (CNNDCI) system to detect cataracts efficiently and effectively. The designed CNNDCI system can perform the cataract identification process accurately in a user-friendly manner using smartphones to collect digital images. In addition, the existing numerical results provided by the literature were used to demonstrate the performance of the proposed CNNDCI system for cataract detection. Numerical results revealed that the designed CNNDCI system could identify cataracts effectively with satisfying accuracy. Thus, this study concluded that the presented CNNDCI architecture is a feasible and promising alternative for cataract detection.
Image defogging is a technique used extensively for enhancing visual quality of images in bad weather conditions. Even though defogging algorithms have been well studied, defogging performance is ...degraded by demosaicking artifacts and sensor noise amplification in distant scenes. In order to improve the visual quality of restored images, we propose a novel approach to perform defogging and demosaicking simultaneously. We conclude that better defogging performance with fewer artifacts can be achieved when a defogging algorithm is combined with a demosaicking algorithm simultaneously. We also demonstrate that the proposed joint algorithm has the benefit of suppressing noise amplification in distant scenes. In addition, we validate our theoretical analysis and observations for both synthesized data sets with ground truth fog-free images and natural scene data sets captured in a raw format.
Nikon has developed various cameras, NIKKOR lenses and accessories, and the technology associated with them, through dialogue with the market, from the film camera era Nikon I(1948)to the latest ...Z-series mirrorless digital cameras.
Processing of images captured by a digital camera showed to be useful in studying the microstructure (porosity characteristics and fractal dimension) of leavened baked products. Five different ...samples were baked including a control and 4 other samples in which wheat flour was partially replaced with other plant flours. Pasting temperature (°C) ranged from 72.94 to 76.25 with chickpea flour showing the highest value. The sample containing amaranth flour presented high porosity (8.23%) with high number of large pores. Whereas, the number of pores was highest for teff flour with 209 pores. This is an indication of weak potential of amaranth flour in stabilizing gas cells. The fractal dimension ranged from 1.644 to 1.683, where amaranth flour showed the lowest fractal dimension. The pore characteristics evaluation, pore size distribution, number of pores, mean area and largest area of pores were influenced when gluten was reduced. Processed images proved that coalescence can be a cause of large pore development when gluten is partially removed.
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•Digital camera showed effective to study gas cells geometry in baked foods.•Non-gluten plant proteins weakened stability of gas cells during baking.•Fractal dimension and pore size distribution corelated to gas cell stability.•Pasting properties were significantly influenced by reducing gluten.
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