Detailed explanation of two technologies of wide dynamic camera

In recent years, with the improvement of people's living standards, security monitoring has received more and more attention, and more and more environments need to be equipped with monitoring equipment. The technology of cameras has also been constantly upgraded with each passing day, better meeting the needs of various monitoring environments. Among them, wide dynamic cameras are an important representative of a branch. In situations where the contrast between light and dark is too large and the light source is single, wide dynamic cameras can show their strength and restore clear essential images for users. Therefore, they are valued by many manufacturers. This article analyzes the reasons why wide dynamic cameras are valued from a technical perspective?

It is hard to tell how many generations of wide dynamic cameras have gone through. In terms of technology, excluding backlight compensation technology, there are two important ways to achieve wide dynamic: CCD+DSP technology and CMOS+DPS technology.

CCD+DSP technology:

DSP chip is a special microprocessor. According to the mathematical model and algorithm of digital signal processing theory, a special digital signal microprocessor chip is designed. The calculation program is all "hardened", and other devices required for digital filters are also integrated and hardened, such as adders, memories, controllers, input/output interfaces, and even other types of external devices. Many tasks that cannot be performed in analog signal processors can be performed in digital processing, such as two-dimensional digital filtering, digital dynamic image detection, digital background light compensation, skin color contour correction, detail compensation frequency adjustment, accurate color matrix, precise correction, automatic focus, etc.

Super wide dynamic technology often uses dual-speed CCD with DSP processing. The core of this double exposure (or double shutter) technology is that for scenes with large light and dark contrast, the camera first quickly exposes the bright area to obtain a clear and normal image of the bright area and stores it in the data buffer memory; then slowly exposes the dark area in the scene to obtain a clear image of the dark area and also stores it in the data buffer memory. After the above exposure is completed, the DSP's unique image processing algorithm is used to cut out the parts of the two images with appropriate brightness, and finally superimpose and synthesize them to output an image with clear light and dark areas. In this way, the problem of overexposure of bright areas and underexposure of dark areas can be avoided, so that the entire picture is clearly visible to achieve the wide dynamic processing effect. However, if different DSP chips are used, there are still obvious differences in specific details, such as the processing of sensitivity, color reproduction, white balance, etc.

CMOS+DPS Technology

Based on the technological development of Stanford University in the 1990s, Pixim, an American company, has developed a new image pickup system based on CMOS technology - DPS (Digital Pixel Processing System). This system can obtain high-quality pictures through its super wide dynamic function. The wide dynamic function has epoch-makingly improved the image shooting effect of bright and dark areas in an image, and can achieve a more realistic and clearer image than CCD. In wide dynamic processing, DPS uses each pixel to expose and ARM7 control technology, which has a higher dynamic range than CCD's double exposure imaging. From a numerical point of view, the dynamic range of CMOS cameras using DPS technology can reach 95dB or even 120dB based on the current processing technology. While expanding the dynamic range, DPS also solves the shortcomings of CCD sensors in processing dynamic range and color authenticity. Its color reproduction is more realistic and can meet the requirements of applications. Cameras using this technology use an analog-to-digital converter (ADC) in each pixel of the digital image sensor, which directly converts the captured light signal into a digital signal, minimizing the attenuation and interference of the signal in the arrangement.

The wide dynamic range of DPS technology has significantly improved the image capture effect of bright and dark areas in an image, and can achieve a more realistic and clearer image than CCD. Due to the single pixel exposure and ARM7 control technology used by DPS, it has a higher dynamic range than CCD's double exposure imaging. And because of the technology of processing each pixel separately, DPS also solves the problem of insufficient color reproduction when processing the dynamic range of CCD sensors.

However, it should also be pointed out that since DPS is a technology based on the individual processing of each pixel, each pixel contains a complete set of processing circuits, which greatly reduces the photosensitive area of ​​each pixel, that is, the amount of light is reduced. As a result, the sensitivity of cameras based on CMOS and DPS technology is significantly affected, or is not very satisfactory.

Comparing with CCD wide dynamic technology, Fan Qinghua, marketing manager of ApVision, said: "It is worth noting that due to the inherent characteristics of CCD, even with multiple exposures, the wide dynamic range of CCD cameras is only 66dB at most, while the dynamic range of CMOS wide dynamic cameras is said to be able to reach more than 120dB. In the future, CMOS wide dynamic technology will have greater room for development."

Conclusion:

As a very practical wide dynamic camera, the development of technology will inevitably be improved. In short, only the continuous improvement of wide dynamic technology itself can be accepted by more users and enter thousands of households.