A brief analysis of the future development of wide dynamic video surveillance camera technology

Since the range of natural light is from 120,000 Lux to 0.00035 Lux on a starry night, the indoor illumination is 100 Lux, while the illumination of the scenery outside may be 10,000 Lux. Therefore, when the camera looks out the window from indoors, the contrast between the two is 10,000/100 = 100: 1. This contrast can be easily seen by the human eye because the human eye can handle a contrast ratio of 1000: 1, but traditional security surveillance cameras cannot because they only have a contrast ratio of 3: 1.

Therefore, when using security surveillance cameras in scenes with large light-dark contrast or backlight, the bright areas of the entire image will be overexposed and the dark areas will be underexposed, and the brightest and darkest parts of the image will not be clearly visible. This is the case in bank savings offices, entrances and exits of important places, etc. Because the strong light from the window and the soft light from the fluorescent lamp on the ceiling may make it difficult to capture the indoor and outdoor scenes at the time, it is impossible to clearly capture the indoor and outdoor scenes with large contrast at the same time.

The images captured will have the background too bright and the foreground too dark, or the background is clear and the foreground is too dark, or the foreground is suitable and the background is too bright. The earliest solution generally used backlight compensation technology or set up two cameras indoors and outdoors to adapt to the large light contrast, but the effect was not ideal. The technology of extending the dynamic range came into being, which is now called wide dynamic range (WDR) technology.

Panasonic launched the first generation of wide dynamic CCD cameras in 1977, the second generation in 1999, and the third generation of super dynamic CCD cameras from 2003 to 2008. During this period, Sony, JVC, Samsung and others also launched their own wide dynamic CCD cameras. So far, the security monitoring industry has been driven by repeated technological reforms.

CCD wide dynamic technology uses a special DSP (digital signal processing) circuit to expose the bright part with the most appropriate shutter speed, and then expose the dark part with the most appropriate shutter speed, and then recombines the two images through DSP processing, so that both the bright part and the dark part can be seen clearly. Although this 160 times dynamic range technology has the advantages of large wide dynamic range and optimization of image grayscale, it has high requirements on DSP performance (especially processing speed). At present, due to the characteristics of CCD, even if multiple exposure sampling is used, the wide dynamic range of the camera can only reach 66dB.

Obviously, due to the limitation of CCD's photosensitivity, it is difficult to make a major breakthrough in technology, but CMOS camera may have outstanding performance due to the excellent performance of its image sensor. For example, the dynamic range of general linear output mode can reach 40~60dB;

Dalsa of Canada uses the IM28-SA CMOS camera with linear-logarithmic output mode, and its dynamic range can reach up to 120dB; Apical Co., Ltd. combines Altera's CycloneIII and CycloneIVFPGAs, and uses the AptinaMT9M033720pWDRCMOS image sensor to launch a CMOS wide dynamic camera that can clearly see both bright and dark parts;

PIXIM of the United States has developed CMOS-DPS technology, and its chipsets from D1000, D1500, D2000 to D2500 have seen rapid improvements in performance: image clarity has increased from 480 lines to more than 540 lines; minimum illumination has increased from 1.0Lux/F1.2 to 0.5Lux/F1.2; typical wide dynamic range has increased from 95dB to 120dB. According to sources, some CMOS wide dynamic range technologies have even reached 160dB.

Therefore, it is foreseeable that future surveillance cameras will be wide dynamic cameras, and wide dynamic technology will belong to CMOS.