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Overview: Image mosaic is the process of combining two or more images with an overlapping field of view in the same scene to produce a seamless panorama or high-resolution image. The image obtained by mosaic has a larger field of view (FOV). Most of the cameras have a FOV angle of about 35 × 50 degrees, which limits the acquisition of information. Therefore, through image mosaic, the continuous image sequence of the same scene is stitched to form a composite image with a larger FOV, which can obtain all visual information at a given point of view at one time. This technology plays an important role in many fields, such as geological survey, medical minimally invasive surgery, and virtual reality. Its technical advantages are obvious. Researchers at home and abroad have done a lot of researches on image mosaic, and image registration is the key step. At present, there are mainly three classical registration methods based on frequency domain, gray level, and feature points, respectively. Nevertheless, the above image registration algorithms generally have the problems of large computational load and low execution efficiency. In this regard, some domestic researchers have proposed a camera calibration method, which saves most of the time needed for stitching and achieves high stitching accuracy.
But at present, the mosaic algorithm based on camera calibration is limited by the scene, and the calibration process is complex. The collinear condition in imaging will be destroyed after image transformation, which is not conducive to subsequent image processing and information classification. For this reason, a cylindrical image mosaic method based on fast camera calibration in multi-scene is proposed. This method makes full use of the high accuracy of feature extraction of checkerboard calibration board, which is used to make it in the overlapping field of view of two adjacent images. In order to accurately and quickly solve the registration parameters between the images to be spliced, the image sequence is pre-processed by corner extraction, precision and matching. Then, cylindrical projection and multi-band fusion are used to maintain visual consistency and detailed information. The system is based on a Low-Power Embedded platform, which achieves fast acquisition and accurate mosaic of camera calibration parameters in multi-scene. The experiment results show that the proposed method can accomplish camera calibration quickly and accurately in indoor and tunnel scenarios, and the image mosaic process is time-consuming. Meanwhile, it can ensure better stitching accuracy and imaging effect, and has strong robustness.
The proposed method has positive significance for real-time image stitching without feature points or large environmental changes.
The calibration parameter acquisition flow chart
The geometric model of pinhole imaging
3D diagram of image projection transformation
The algorithm framework of image mosaic
The sketch of cylindrical projection transformation
The sketch of cylindrical projection transformation
The diagram of Image overlay
The sketch of multi-band fusion
The hardware system diagram
Experimental platform
The stitching results. (a) The mosaic image in indoor; (b) The mosaic image in tunnel
The time bar chart of splicing process
Stitching results without cylindrical projection transformation
Rotary platform in roll direction (a) and pitch direction (b)
The experimental results of roll direction pixel focal length (a) and shift value (b)
Comparisons of splicing results in roll and pitch direction
The experimental results of pitch direction pixel focal length (a) and shift value (b)
Stitching results of different positions of the calibration plate