Wide dynamic technology In some situations where the contrast between light and shade is too large, the general camera is limited by the sensitivity of CCD, and the image captured by the camera often has a bright background or a dark foreground. In view of this situation, wide dynamic technology came into being and solved this problem well. Before that, traditional cameras generally used backlight compensation function to adapt to situations with large light contrast.

When an object in the field of view of a conventional camera needs to look at the object outside the door or window when the background light is high in brightness, the central backlight compensation (BLC) mode is usually used. It mainly depends on improving the brightness of the central part of the field of view and reducing the brightness of the surrounding parts of the field of view to see the object in the central position.

The wide dynamic technology is exposed twice at the same time, one time fast, one time slow, and then composite to see the bright and dark objects on the screen at the same time. Although both are measures taken to overcome the problem of seeing the target clearly in a strong backlight environment, backlight compensation is at the cost of sacrificing the contrast of the image, so in a sense, wide dynamic technology is an upgrade of backlight compensation.

You can see that the difference between using wide dynamic technology and not using wide dynamic technology is very obvious. Because of this characteristic, wide dynamic technology is usually used in the camera of road monitoring. However, with the development of smart phones, we all know that the pixels of smart phones are getting higher and higher, and the phone users are increasingly demanding of the phone's photo taking function, so some functions originally on professional devices have also been transplanted to mobile phones. So how is this wide dynamic technology used on mobile phones? Xiao Bian found Mr. Xu Yongsong, the technical director of Ningbo Sunny Optoelectronic Information Co., Ltd., which has an international reputation in the field of mobile camera.

Wide dynamic technology Mobile camera The working principle of the CMOS image sensor is as follows: fast readout CMOS image sensor is required for wide dynamic range. With CCD image sensor, the user is restricted to use continuous 1/60s or twice 1/30s odd and even field synthesis. In the new wide dynamic technology, users can use the long exposure of 1/30s pictures and the short exposure of 1/30s pictures, and then process these two pictures in real time to obtain an industrial level image with wide dynamic range.

The following is an illustration:

In addition to the above methods, some people are developing different methods to obtain wide dynamic effects. One of them is called dynamic response pixel technology. This technology focuses on the DR inside the image, that is, different sensitivity is added to each pixel. The principle of this pixel is that it has a large charging capacitor.

When the image is highlighted, the DCG switch is turned on and connected to the physical capacitance of the FD node. In this way, the large capacitance of the FD node enables the LCG mode, that is, it can hold a large number of signals to charge (without overflowing). Under the condition of low illumination, the DCG switch is turned off to disconnect the capacitance connected to the FD node, enabling the HCG mode, that is, to use the additional analog gain inside the pixel. In this case, the FD capacitance only depends on the PN junction capacitance and metal mutual capacitance of the FD, which is much smaller than the physical capacitance structure. Fewer FD capacitors will increase the conversion gain, improve the sensitivity and reduce the read noise at the expense of reducing the maximum charge holding capacitance.

Related reading:

Detailed explanation of optical anti shake of mobile camera

Aikepu: composition structure of mobile camera

This is going against the weather! Find 5 uses a stacked CMOS sensor