Photos taken in dark light show that the photos are dimmed with a small number of noises. At present, all mobile phones restore the authenticity of night scenes by increasing the ISO sensitivity of cameras. The smartphone automatically adjusts ISO sensitivity according to the ambient brightness. The ISO sensitivity of the camera is automatically increased if the ambient brightness is low or dark, but the noise is also magnified at the same time. Therefore, granular phenomena such as dots and black spots may occur on the screen. When the overall brightness is relatively dark, the camera automatically enters the special mode of "brightening the night scene" to increase the ISO sensitivity of the camera, and at the same time amplify the noise, but the overall brightness will be greatly increased.