We propose a sprite generation scheme for video surveillance system. We generate a sprite by using the proposed blending algorithm based on cylindrical coordinate system.
In general, there are three major steps in sprite generation. First, global motion is estimated between each neighboring image pair. Second, images are warped to a fixed coordinates with the global motion parameters. Finally, each pixel value in the sprite is obtained by blending all the corresponding pixels from the input images. Among these steps, we focus on how to select the reference coordinates and how to blend the overlapping images.
The cylindrical coordinates is recommended for an image sequence obtained by a panning camera. Since the total size of sprite increases as the radius of cylinder is increased and the resulting sprite may lose the pixel information as the radius is decreased, the determination of the appropriate radius of cylinder is very important. We claim that the focal length of the camera in pixel unit is the best choice for the radius and propose a simple but effective algorithm to estimate the focal length in pixel unit
As we know, lens distortion of camera is minimum at the center of an image and warping error increases as a pixel locates far from the center of an image. It means that using all pixel information of an image is not a good choice in blending. Therefore, we propose a selective blending algorithm that uses minimum strips closest to the center of an image for generating a sprite.
We verify that a cylindrical coordinates sprite generated by the proposed scheme shows higher PSNR than that of Cartesian coordinates sprite. Also, the sprite using the proposed blending algorithm reduces blurring and deterioration in the image.
