1 Introduction to Digital Rear-View Mirror -CMS
Camera Monitor Systems (CMS) utilize the camera, image processing, and display screen technology, replacing traditional vehicle rear view mirrors to provide drivers with a wider and clearer field of vision, assisting them in better observing their surroundings. Starting from July 2023, according to the regulations of the GB15084-2022 Chinese national standard, the performance and installation of indirect vision devices for motor vehicles need to meet corresponding requirements. Among these requirements, latency becomes one of the key focal points of CMS systems.
2 Challenges of Latency
In CMS, latency refers to the time consumption from the occurrence of an event to its perception by the sensor, processing through ISP, and displaying on the screen. It directly affects the driver's real-time judgment of the rear environment. If the latency is too high, it may result in inaccurate judgment of the rear traffic conditions or missing important information, thereby increasing the risk of accidents.
The comparison of existing solutions is shown in the following table:
The relative speed value is set at 120 km/h (33.3 m/s), considering the speed difference between two vehicles during highway merging. According to the national standard GB/T 12673-2019, the standard size length of a passenger car is between 3.8m and 4.3m. The distance difference for a 100ms latency is approximately 3.33m, as shown in the diagram:
A latency exceeding 100ms poses a certain level of danger.
In the case of other vendors' solutions, the latency is above 35ms, resulting in a distance difference of more than 1.16m, as shown in the diagram:
Point Spread Technology reduces the latency to below 20ms and narrows the distance difference to within 0.66m.
3 Point Spread Technology Full Parallel ISP Reduces System Latency
The theoretical calculation formula for total latency is as follows:
[Total Latency = Came ra Latency + Total Latency = Camera Latency + Image Processing Latency + Display Screen Latency]
The camera and display screen latency are fixed values that cannot be changed. The core advantage of Point Spread CMS is the self-developed fully parallel heterogeneous ISP and image quality enhancement IP, which can reduce the signal processing latency to 1ms, thereby reducing the total latency. The schematic diagram of the CMS system is as follows:
4 Technical Verification and Experimental Results
Our research and development team conducted rigorous experimental verification. By capturing the circuit board and display screen, and measuring the positional difference of the lights, we calculated the final latency result. The experimental results show that our total latency is only 18ms, surpassing the industry standard.
Experimental Materials:
1 A circuit board with 10x10 flashing lights at 1ms intervals
2 Display screen (replaceable with lower latency display screen according to OEM requirements)
3 Point Spread Technology self-developed ultra-low latency CMS system
4 High-speed camera
Experimental Procedure:
The circuit board is shown in the following diagram, with the flashing area composed of a 10x10 array of lights. From 1ms to 100ms, each light sequentially lights up from right to left, and from bottom to top. The counting area consists of three rows: the first row counts in 0.1s (100ms) units, the second row counts in 1s units, and the third row counts in 10s units.
Experimental Principle:
By randomly sampling the position of the lights in the display screen and comparing them with the position of the lights in the circuit board, we can obtain the total latency value.
Experimental Process:
1 Turn on the circuit board.
2 Align the camera lens with the circuit board.
3 Capture the circuit board and display screen with a high-speed camera.
4 Measure the positions of the lights in the circuit board and display screen.
5 Calculate the final latency.
Experimental Results:
