Smartphone camera fundamentals

We know that the currently used mobile phone cameras are all derived from digital cameras. They are actually the products of bionics, and digital cameras are the simulation of human eyes. Normal human eyes can see objects at different distances, adapt to the brightness of night and day, and can see colorful things. Therefore, in order to effectively imitate the human eye, the ultimate goal of a digital camera is to achieve three points: seeing distance, distinguishing light and dark, and recognizing color.

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For example, excluding myopia and other conditions, the normal human eye has the ability to see the distant view and the near view. The corresponding camera ability is focusing. The digital video camera follows the focusing method of the human eye, and realizes the switching between the far and near scenes by changing the focal length.

Comparison of camera and eyeball structure

It can be seen from the above figure that the front glass of the camera, commonly known as lens, corresponds to the lens of the eye, and the photosensitive element of the camera, commonly known as sensor, corresponds to the retina of the human eye. In order to imitate the focus of the eyes, there is a concept of AF in the digital camera, the purpose is to enable the digital camera to achieve real-time automatic focus on the objects in the scene. In terms of physical optics, there are generally two ways to change the optimal imaging distance: changing the focal length of the lens or changing the distance from the lens to the sensory element. Digital cameras use motors to control the distance between the lens lens and the photosensitive sensor to achieve focus.

(3) After talking about how to achieve distance, the next step is to enable the digital camera to distinguish between light and dark. Everyone should have had this experience. When you wake up in the morning and open the curtains on a sunny day, you will feel very dazzling, but after a while, you can get used to the brightness. The ability to quickly switch between light and dark is due to the pupils of the human eye. By shrinking and dilating the pupils, the amount of incoming light can be controlled to adapt to different brightness environments. Generally, high-end SLR cameras have a concept of aperture, which actually transfers the function of the pupil to the camera.

However, the cameras on our mobile phones do not integrate the physical aperture due to problems such as cost, size, and craftsmanship. In fact, it is realized through digital signal processing. Since the response of brightness on the electronic photosensitive device is a bunch of numbers, the larger the number, the greater the brightness. Then when the camera finds that the environment is relatively dark, the brightness data can be multiplied To brighten with a larger coefficient, this concept is the digital gain Gain. When using a digital camera, it is the concept of ISO. The larger the ISO, the greater the digital brightening. Another way to control the brightness is the time for the sensor to feel the brightness. The longer the time, the brighter the picture will be, which is commonly known as the exposure time. When the ambient brightness is different, the digital camera can adjust the brightness of the photo by adjusting the exposure time and digital brightness gain, which together constitute the automatic exposure function AE of the digital camera.