Dataset Information

A Novel Camera Calibration Method Based on Polar Coordinate.

ABSTRACT: A novel calibration method based on polar coordinate is proposed. The world coordinates are expressed in the form of polar coordinates, which are converted to world coordinates in the calibration process. In the beginning, the calibration points are obtained in polar coordinates. By transformation between polar coordinates and rectangular coordinates, the points turn into form of rectangular coordinates. Then, the points are matched with the corresponding image coordinates. At last, the parameters are obtained by objective function optimization. By the proposed method, the relationships between objects and cameras are expressed in polar coordinates easily. It is suitable for multi-camera calibration. Cameras can be calibrated with fewer points. The calibration images can be positioned according to the location of cameras. The experiment results demonstrate that the proposed method is an efficient calibration method. By the method, cameras are calibrated conveniently with high accuracy.

SUBMITTER: Gai S

PROVIDER: S-EPMC5087901 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Publications

A Novel Camera Calibration Method Based on Polar Coordinate.

Gai Shaoyan S Da Feipeng F Fang Xu X

PloS one 20161031 10

A novel calibration method based on polar coordinate is proposed. The world coordinates are expressed in the form of polar coordinates, which are converted to world coordinates in the calibration process. In the beginning, the calibration points are obtained in polar coordinates. By transformation between polar coordinates and rectangular coordinates, the points turn into form of rectangular coordinates. Then, the points are matched with the corresponding image coordinates. At last, the paramete ...[more]

PMID: 27798651

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Project description:An alternative to the conventional method of performing the AAPM Report 52 rotational uniformity and sensitivity test has been developed. In contrast to the conventional method in which a Co-57 sheet source is fastened to the collimator, this new point-source method acquires the images intrinsically using a Tc-99m point source placed near the isocenter of gantry rotation. As with the conventional method, the point-source method acquires 5 x 10(6) count flood images at four distinct gantry positions to calculate the maximum sensitivity variation (MSV)--a quantitative metric of rotational uniformity and sensitivity variation. The point-source method incorporates corrections for the decay of Tc-99m between acquisitions, the curvature in the image intensity due to variation in photon flux across the detector from a near-field source, and the source-to-detector distance variations between views. The raw point-source images were fitted with an analytic function in order to compute curvature- and distance-corrected images prior to analysis. Five independent MSV measurements were performed using both conventional and point-source methods on a single detector of a dual-headed SPECT system to estimate the precision of each method. The precision of the point-source method was further investigated by performing ten independent measurements of MSV on six different detectors. Correlation between the MSV calculated by the two methods was investigated by performing the test on nine different detectors using both methods. Different levels of sensitivity variations were also simulated on four detectors to generate 40 additional paired points for correlation analysis. The effect of the total image counts on the MSV estimated with the new method was evaluated by acquiring image sequences with 5 x 10(6), 10 x 10(6), and 20 x 10(6) count images. The MSV calculated using the conventional and point-source methods exhibited a high degree of correlation and consistency with equivalence. The precision of the point-source method (0.145%) is lower than the conventional method (0.04%) but sufficient to test MSV. No statistically significant dependence of MSV with the point-source method on the total image counts over a range of (5-20) x 10(6) counts was observed. Curvature correction of the images prior to the generation of difference images renders images more conducive to qualitative inspection for structured, nonrandom patterns. The advantages of the new methodology are that multiple detectors of a gamma camera can be evaluated simultaneously which substantially reduces the time required for MSV testing and the reduced risk of accidental damage to the collimators and patient proximity detection system from having to mount a sheet source on each of the detectors.

Dataset Information

A Novel Camera Calibration Method Based on Polar Coordinate.

Publications

A Novel Camera Calibration Method Based on Polar Coordinate.

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