Since each image is captured by the camera at different angles, they are not on the same projection plane. If the overlapped images are seamlessly stitched directly, the visual consistency of the actual scene will be destroyed. So images need to be projected and transformed firstly, and then stitched. Generally, there are plane projection, cylindrical projection, cube projection and spherical projection.
The plane projection is based on the coordinate system of an image in the sequence image, and the image is projected into the reference coordinate system, so that the overlapping area of the adjacent image is aligned, and this stitching is plane projection stitching; Cylindrical projection refers to such projection stitching that the acquisition of image data re-projection to a cylinder with focal length of camera, and then make the projection of the panorama on the cylinder surface; Spherical projection is to simulate the characteristics of human eye observation, project image information onto the eye part through the perspective of transformation projection, construct as an spherical of observation; Cube projection is a kind of projection stitching method developed to solve the shortcomings of the data storage in spherical allusions, it is suitable for computer-generated images, but for the real shot images is more difficult. As shown in Figure 4, the images stitching process flow diagram.