Wide dynamic monitoring camera CCD/CMOS-DSP analysis

The wide dynamic camera has undergone several generations until now, failing to speak clearly. In terms of technology, it does not count the backlight compensation technology. There are two important implementations of wide dynamics: CCD+DSP technology and CMOS+DPS technology.

CCD+DSP Technology:

The 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 all other equipment required by the digital filter is also integrated and hardened, such as adder, memory, controller, input/output interface, 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, Accurate correction, auto focus and more.

Super wide dynamic technology often uses two-speed CCD with DSP processing. The double-exposure (or double-shutter) technology focuses on the scene with large contrast between bright and dark. The camera first performs a quick exposure on the bright area to obtain a clear and normal image in the bright area and stores it in the data buffer memory. Then a slow exposure is performed on the dark area in the scene, and a clear image with a dark area is also stored in the data buffer memory. After the above exposure is completed, using the DSP-specific image processing algorithm, the brightness of the two images is properly cut off, and finally a superimposed synthesis and output of an image clearly visible in light and dark areas. In this way, the problem of overexposed light and dark underexposure can be avoided, so that the entire picture is clearly visible to achieve a wide dynamic processing effect. However, if different DSP chips are used, there are obvious differences in specific details, such as the processing of sensitivity, color reduction, white balance, and the like.

CMOS+DPS Technology

Based on the technological development of Stanford University in the 1990s, Pixim Corporation developed a new image pickup system based on CMOS technology, DPS (Digital Pixel Processing System), which can be obtained through its ultra-wide dynamic function. High quality pictures. The wide dynamic feature dramatically improves image capture in bright and dark areas of an image, allowing it to achieve more realistic and sharper images than CCDs. In wide dynamic processing, the DPS uses a single exposure and ARM7 control technology for each pixel, and has a higher dynamic range than the double exposure imaging of the CCD. Numerically speaking, the CMOS camera with DPS technology can achieve 95dB dynamic range or even 120dB with current processing technology. While expanding the dynamic range, DPS has also solved the deficiencies of the CCD sensor in dealing with the dynamic range and color authenticity, its color reproduction is more real, can meet the application requirements. Cameras using this technique use an analog-to-digital converter (ADC) in each pixel of the digital image sensor. When an optical signal is captured, it is directly converted to a digital signal, minimizing the attenuation of the signal in the array. And interference.

The wide dynamic capabilities of DPS technology dramatically improve image capture in bright and dark areas of an image, allowing it to achieve more realistic and sharper images than CCDs. Due to the single pixel exposure and ARM7 control technology used by the DPS, there is a higher dynamic range than the double exposure imaging of the CCD. Because each pixel of DPS has its own processing technology, it also solves the problem of inadequate color reproduction caused by the CCD sensor's handling of dynamic range.

But also need to point out, because DPS is based on the technology of each pixel processing alone, because each pixel contains a complete set of processing circuits, which also greatly reduces the photosensitive area of ​​each pixel, that is, the reduction in the amount of light, which The result is a camera based on CMOS and DPS technology, the sensitivity of which is significantly affected or not very satisfactory.

By contrasting CCD wide dynamic technology, Fan Qinghua, marketing manager of Apex Vision, stated: "It is worth noting that due to the inherent characteristics of CCDs, even with multiple exposures, the wide dynamic range of CCD cameras is only 66dB at most, and The CMOS wide dynamic camera is reported to have a dynamic range of more than 120dB. In the future, CMOS wide dynamic technology will have more room for development."

Conclusion:

As a very practical wide dynamic camera, the development at the technical level will inevitably strive for excellence. In short, only the continuous improvement of the wide dynamic technology can be accepted by more users, and thus into millions of households.