The Meaning of 120dB Wide Dynamic

We often see that the parameters of the camera say that it supports 120dB wide dynamic, where 120dB is actually a ratio, which means that the ratio of the illuminance between the brightest part and the darkest part of the camera can be identified as 1 000 000:1, that is, 106: 1.

Why is 106:1 corresponding to 120dB? Because of our artificially defined wide dynamic ratio formula:

dB = 20 log (illuminance of brightest part [lx] / darkest part [lx] )

20log(1 000 000/1)=20 X 6=120dB

In essence dB is a ratio, a pure counting method, without any unit notation. It has different names in different fields, so it also represents different practical meanings. Such as sound volume, signal strength, etc.

The meaning of dB is to represent a very large number (followed by a long string of 0s) or very small (with a long string of 0s in front of it) relatively short. For example, expressing a wide dynamic range as 120dB is obviously more intuitive and concise than using 1 000 000:1.

Other fields, for power, dB = 10Xlog(). For voltage or current, dB = 20Xlog().

In the field of security, 120dB is also a special ratio, and the dynamic range that the human eye can recognize is about 120dB. This means that a camera with a wide dynamic capability of 120dB can recognize a dynamic range comparable to that of the human eye.

Application scenarios of wide dynamic cameras

In the field of security video surveillance, the wide dynamic range of the camera has always been a very important function. Especially in some special industries or scenarios, the wide dynamic function must be used. For example, a miniature pinhole camera installed in a bank ATM machine to monitor users, because the camera is generally illuminated from indoors to outdoors, and the contrast between light and dark is strong, and it is difficult for ordinary cameras to see the face clearly, so a camera with dynamic bandwidth function must be used. . For another example, a camera installed in a hotel lobby illuminates the entrance and exit of an outdoor lobby from indoors. In order to clearly see the characteristics of people entering and leaving, especially facial features, a camera with dynamic bandwidth function must be used.

Entrance with daylight outside and shaded interior.

Parking lots or tunnels with daylight outside and low levels of interior brightness.

Outdoor scenes with direct sunlight and dark shadows.

Office buildings or shopping centers with lots of windows that reflect light.

other names

Wide dynamic, WDR (wide dynamic range), that is, wide dynamic range. After the security sensor entered the CMOS era, wide dynamic range is also called HDR, that is, High-Dynamic Range. Especially in the film and television industry, the field of displays, mobile phone screens, photography, etc. are generally referred to as HDR. The security industry also refers to wide dynamic range as HDR, which is in line with these industry fields.

Sony, which leads the development trend of security sensors, also has these names for the wide dynamic function: DOL-HDR or DOL-WDR, both of which mean the same thing.

Difference from Backlight Compensation

The problem solved by backlight compensation is that the monitoring target is too dark and cannot be seen clearly because of the strong background light. When backlight compensation is turned on, the target object in the foreground can be seen clearly, while the previously bright areas will be overexposed.

WDR means that the entire frame is clearly visible, with no overexposed areas and no areas that are noticeably darkened.