practice how to describe a process At first, a image is captured by the camera and transferred to a program, by which the image data will be transformed and then stored in cache memory. These data keep staying in cache until five images are captured. Then the program reads all of these five frames at one time to do further calculations and finally get one frame. During this process it needs to use some parameters, which are detected by another device. HID APIs are implemented to get this job done. At last, when an image is ready, system calls function to display it on the screen.