[Knowledge of visual reversing image]Evaluation index of vehicle-mounted ccd camera

Mainly include pixel value, signal-to-noise ratio, cooling temperature, etc.
Signal-to-noise ratio (SNR)
The true signal-to-noise ratioCameraThe detection capability. In order to improve the performance of the camera, all CCD camera manufacturers try their best to maximize the signal (the number of electrons that can reach the full well) while reducing noise as much as possible.
SNR = full well electronics / noise electronics = dynamic range = maximum gray scale = 2bit number
In the same full-well electronic CCD, reducing the CCD noise can improve the CCD's monitoring ability. Heat or dark current is noise to the CCD, and the noise can basically be eliminated by the deep cooling Peltier in the Cool CCD. When the exposure exceeds 5-10 seconds, the CCD chip will heat up. Without a cooling device, the "hot" or white pixels will cover the image, and snowflakes will be seen everywhere in the image. The -20°C camera can take up to 5 minutes of images, and the -40°C camera can take more than 1 hour.
CCD structure design, digitization method, etc. will affect the generation of noise. By improving the structure and optimizing methods, the generation of noise can also be reduced.
Pixel area
This indicator is an important indicator in the chip. The larger the pixel area, the more sensitive it is to light. Because there are more electrons in the pixel area, more signals can be generated. Large pixels increase sensitivity, and small pixels increase resolution. To improve the image quality, it is necessary to increase the pixels of the CCD. Therefore, when the size of the CCD is fixed, increasing the pixels means reducing the photodiodes in the pixels. We know that the smaller the area of ​​the unit pixel, the lower the photosensitive performance, the lower the signal-to-noise ratio, and the narrower the dynamic range. Therefore, this method cannot increase the resolution indefinitely. Therefore, if you do not increase the CCD area and blindly increase Resolution will only cause deterioration of image quality. However, if you want to maintain the existing image quality while increasing the CCD pixels, you must increase the total area of ​​the CCD while at least maintaining the unit pixel area. At present, it is more difficult to process and manufacture larger-sized CCDs, and the yield rate is relatively low, so the cost has not been reduced. This contradiction is difficult to overcome for CCDs.
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