According to reports from Electronic Enthusiasts Network (Author: Liang Haobin), recently a blogger on a social platform claimed, “No matter how good digital monitoring is, there is always a delay of half a second to a second, while analog signal transmission monitoring has almost no delay, so automotive backup images must be all analog cameras.”
From a theoretical perspective, digital signal transmission requires the analog signal output from the CIS to be modulated, encoded, and converted into a digital signal before transmission, thus inherently leading to a longer delay compared to analog signals.
However, the question arises: Are automotive backup images really all from analog cameras? Is the delay of digital cameras really that high?
Analog Cameras Remain the Mainstream
Due to mature technology, low delay, and low cost, many vehicles have adopted analog signal transmission for backup images, streaming rearview mirrors, and 360-degree surround views, whether factory-installed or aftermarket. For example, the backup image of the 2021 Toyota Camry uses AHD.
AHD, or Analog High Definition Video Signal Protocol, is an analog HD solution launched by South Korea’s Nextchip company. AHD can reliably transmit 500 meters of HD video signals over existing analog transmission lines, using Y/C signal separation and analog filtering technology to effectively reduce color noise in high-frequency areas and minimize signal interference.
AHD claims to have zero delay, capable of transmitting front-end data without encoding compression to the back end, achieving real-time, high-fidelity output, with AHD 2.0 supporting up to 1080P@30fps.
Of course, in the field of analog HD, there are also two major domestic security giants, Dahua’s CVI (Composite Video Interface) and Hikvision’s TVI, which are very similar to AHD, and both companies have also launched some aftermarket backup image-related products.
Theoretically, the low delay of video analog signal transmission is mainly due to the fact that the CMOS image sensor outputs an analog signal. In products like smartphones and digital cameras, the CIS converts the analog signal to a digital signal through an internal analog-to-digital conversion circuit and outputs it to external devices for processing.
Analog cameras do not require complex encoding and compression, simplifying signal processing to basic tasks like signal amplification, filtering, and adjustment, thus reducing processing steps. Additionally, analog signals are transmitted via coaxial cables, which, as a continuous signal, avoid issues like packet loss and retransmission that can occur in digital signal network transmission, further lowering delay.
Therefore, analog cameras typically have lower delays than digital cameras, a phenomenon that is pronounced in some modern smart vehicles. For instance, many owners have reported perceivable delays in backup images on certain new energy vehicle forums.
On the other hand, delays from the camera to the display include an initial frame delay from the CIS output, signal processing delays, and display screen delays. Factors affecting display screen delays include the frame rate (higher frame rates lead to lower delays) and response times. For example, OLED displays inherently have faster response times than LCDs.
Digital Cameras Will Gradually Replace Analog
Although analog cameras have certain advantages in terms of delay, apart from this single parameter, the advantages of analog signal image transmission have almost been reduced to just lower costs.
In practical applications, FPV drones have higher requirements for transmission delay than cars, and previously, FPV transmissions often used analog signals. However, the image quality of analog transmissions has significant limitations and is susceptible to interference. Today, industry leader DJI is also moving towards digital transmission, achieving low delays while maintaining high image quality.
For example, the DJI FPV Goggles V2 uses a digital transmission system that can achieve image delays of less than 28 ms in low-latency mode at 810p/120fps.
On the other hand, from a parameter perspective, AHD currently can only output up to 1080P@30fps video, which is difficult to meet the requirements in the era of intelligence. First, the algorithms that can be used for post-processing analog images are limited, making it hard to handle complex scenes like backlighting and low light. If an additional analog-to-digital conversion module is added to an analog camera, it will further increase the delay. Digital cameras generally integrate conversion circuits within the CMOS sensor, making their delays almost negligible.
In today’s vehicle cameras, CIS needs to integrate multiple image processing functions with high requirements for image quality, low light, and dynamic range. In high-end ADAS applications of smart vehicles, it is also necessary to eliminate motion artifacts and suppress LED flickering.
This raises higher demands for image processing ISPs while also requiring low delays. Therefore, today’s vehicle CISs typically integrate specialized ISPs to reduce data processing delays.
Thus, despite their higher costs, the greater integration and better display effects brought by the addition of ISPs are causing analog cameras to gradually withdraw from the automotive market.
In terms of delay, some current vehicle camera applications have also achieved levels of delay that are difficult to perceive. According to the national standard requirements of “Road Vehicles – Ergonomics and Performance Aspects of Camera Monitoring Systems – Requirements and Test Procedures” (ISO 16505-2019), the delay of electronic rearview mirrors should be less than 200 ms, which is consistent with current European standards.
Currently, domestic Tier 1 supplier Desay SV has electronic rearview mirror system-level products that can achieve system delays within 60 ms, while previously demonstrated electronic rearview mirror solutions by Dianyun Technology can achieve delays as low as 20 ms.
While analog cameras have some advantages, their overall performance has a lower ceiling, and their development space is relatively small. In current applications, high resolution, high frame rates, and high dynamic ranges have become core demands for automotive and other terminal applications. With technological advancements, delay issues are continuously being optimized. Therefore, evaluating a technology needs to be based on application scenarios, and ultimately, market feedback will determine the direction of technology development.
Disclaimer: This article is original from Electronic Enthusiasts. Please indicate the source above when reprinting. For group discussions, please add WeChat elecfans999. For submission of interviews and reports, please email [email protected].
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