A flexible calibration method based on small planar target for defocused cameras

Huo, Junzhou; Zhang, Haidong; Meng, Zhichao; Yang, Fan

doi:10.1016/j.optlaseng.2022.107125

Cited by 15 publications

(5 citation statements)

References 31 publications

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“…The camera was calibrated using Zhang's method [23] to obtain its intrinsic and extrinsic parameters. To validate the derived formulations, the world dimensions of the stick with respect to its angular displacements are transformed to the camera, image plane, and sensor coordinates in that order, through the characteristic pinhole-camerabased projection matrix in homogeneous coordinates, after which the resulting values are substituted into the formulated equations in Section 2.1 to find the corresponding angular displacements in degrees ( • ).…”

Section: Experimental Validationmentioning

confidence: 99%

“…The identified imaging length X P is substituted into Equation (18) to acquire the yaw angle α at each REV1# case. The left and right limits are calculated as 90 • and −13.0 • according to Equation (22) and Equation (23). The detection model from yaw angle to imaging length, and the inversion model, are respectively denoted as the dashed red line and solid blue line in Figure 20.…”

Section: Validation Of Pure View Casesmentioning

confidence: 99%

See 1 more Smart Citation

Wind Speed Measurement via Visual Recognition of Wind-Induced Waving Light Stick Target

Zhou

Kasimu

et al. 2023

Applied Sciences

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Wind measurement in confined spaces is a challenge due to the influence of the dimensions of anemometers in intrusive flow-field measurements where the anemometer probes directly contact and influence the near-probe flow field. In this work, a new wind speed detection methodology is proposed based on wind-induced motion of a stick via vision-based recognition. The target’s displacement in pixel coordinates is mapped to its angular displacement in world coordinates to derive wind speed and direction information by applying the calibration coefficients. Simulation experiments were carried out to validate the model, the error of which was within an angular displacement of 4.0° and 3.0° for wind speed and direction detections, respectively. When applied to the measurement of wind speed in the inner equipment cabin of a stationary high-speed train, the error was within ±1.1 m/s in terms of average RMSE. Thus, the proposed method provides an accurate and economic option for monitoring 2D wind in a confined space.

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Section: Experimental Validationmentioning

confidence: 99%

Section: Validation Of Pure View Casesmentioning

confidence: 99%

Wind Speed Measurement via Visual Recognition of Wind-Induced Waving Light Stick Target

Zhou

Kasimu

et al. 2023

Applied Sciences

View full text Add to dashboard Cite

show abstract

“…A small target will lead to a loss of accuracy due to the uneven distribution of feature points on the target. Some methods based on the phase target have been proposed to avoid the above problems, taking advantage of the fact that the control points on the phase target can be identified in the blurred image plane [20][21][22]. However, these methods based on the phase target require additional high-quality monitoring equipment and a series of images in multiple phase attitudes for each target pose.…”

Section: Introductionmentioning

confidence: 99%

Calibration method for binocular vision system with large field of view based on small target image splicing

Li,

Xu,

Zhang

et al. 2024

Meas. Sci. Technol.

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In vision measurement, camera calibration has a significant impact on measurement precision. The classical target-based calibration methods require the target to occupy more than one-third of the field of view. A small-size target that does not meet the requirements results in poor calibration accuracy, while an appropriate large-size target is difficult to manufacture and inconvenient to operate. In view of the above problem, we propose a flexible and accurate calibration method based on small target image splicing to calibrate the binocular vision system with a large field of view. The spliced images and virtual large targets are constructed to extend the target size, providing better flexibility for calibration. Moreover, an optimization objective function integrating two constraints in the imaging plane and measurement space is presented to improve the calibration accuracy during the parameter optimization process. The simulation experiments and actual experiments are carried out to test the performance of the proposed method. The results demonstrate that the calibration accuracy of the proposed method using a small target is equivalent to that of Zhang’s method using a large target. Additionally, when using a same-size target, the parameter error of the proposed method is less than that of Zhang’s method, and the proposed method reduces the distance measurement error from 1.169mm to 0.208mm compared to Zhang's method.

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“…Obviously, all the above methods are primarily for shortdistance vision systems [22], require focusing and occupying a large proportion of the images on the imaging sensor [23]. However, the captured images are typically out of focus for long-distance vision measurements, such as in a tunnel boring machine-like environment [24,25]. The defocused image affects feature extraction accuracy, which contributes to the degradation of calibration performance.…”

Section: Introductionmentioning

confidence: 99%

A stable and effective calibration method for defocused cameras using synthetic speckle patterns

Zhang

Wang

et al. 2023

Meas. Sci. Technol.

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Well-focused and sharp target images are essential in traditional calibration, but they generally cause difficulty and inconvenience in image acquisition in practical applications. To address this problem, a stable and effective calibration method for defocused cameras is proposed in this study. Firstly, the two speckle patterns are created, one of which is with control points to estimate the initial value and the other used for point pair match registration is without control points. They are subsequently displayed on a fixed monitor and captured at each camera pose. Secondly, the initial guess for the control points was estimated using the proposed method. The retrieval of query points can then be done with high accuracy using the digital image correlation (DIC) algorithm. Finally, all the calibration parameters, including lens distortion, were calculated using the plane calibration algorithm. The experiment in this study demonstrated the practicality and effectiveness of the proposed method. The accuracy and precision were quantitatively evaluated by the mean reprojection errors, which were 0.057 pixels.

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A flexible calibration method based on small planar target for defocused cameras

Cited by 15 publications

References 31 publications

Wind Speed Measurement via Visual Recognition of Wind-Induced Waving Light Stick Target

Wind Speed Measurement via Visual Recognition of Wind-Induced Waving Light Stick Target

Calibration method for binocular vision system with large field of view based on small target image splicing

A stable and effective calibration method for defocused cameras using synthetic speckle patterns

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