Abstract
The refractive index of a lens varies for different wavelengths of light, and thus the same incident light with different wavelengths has different outgoing light. This characteristic of lenses causes images captured by a color camera to display chromatic aberration (CA), which seriously reduces image quality. Based on an analysis of the distribution of CA, a full-field calibration method based on absolute phase maps is proposed in this paper. Red, green, and blue closed sinusoidal fringe patterns are generated, consecutively displayed on an LCD (liquid crystal display), and captured by a color camera from the front viewpoint. The phase information of each color fringe is obtained using a four-step phase-shifting algorithm and optimum fringe number selection method. CA causes the unwrapped phase of the three channels to differ. These pixel deviations can be computed by comparing the unwrapped phase data of the red, blue, and green channels in polar coordinates. CA calibration is accomplished in Cartesian coordinates. The systematic errors introduced by the LCD are analyzed and corrected. Simulated results show the validity of the proposed method and experimental results demonstrate that the proposed full-field calibration method based on absolute phase maps will be useful for practical software-based CA calibration.
Highlights
A camera is an indispensable part of optical measurement systems, and it is the key to realizing fast and noncontact measurements
Its color filter is distributed as a strip. It will have the phenomenon a moire fringe when the camera directly looks at the liquid crystal display (LCD) screen
This paper presented a novel method for full-field calibration and compensation for chromatic aberration (CA) among the red, green, and blue channels of a color camera based on absolute phase maps
Summary
A camera is an indispensable part of optical measurement systems, and it is the key to realizing fast and noncontact measurements. Color cameras can simultaneously obtain the color texture and three-dimensional (3D) shape information of an object, which substantially improves the measurement speed. Because of the optical characteristics of lenses, chromatic aberration (CA) exists in the captured images, which seriously affects the quality of the image and the accuracy of the measurement results. To improve the measurement speed, and to obtain a precise color texture and the 3D data of an object’s morphology, the correction of the CA for each color channel has become an inevitable and urgent problem. Using a precise optical calculation, lens grinding, and lens assembly, a lens that focuses light of different colors at the same position is produced, enhancing the clarity and color fidelity of images. The other approach is software elimination, during which the camera captures images and digital image processing is used to correct the color differences
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