What is AHD Analogue High Definition?

What is the difference between traditional reversing cameras, and the latest AHD reversing cameras?

For many years reversing cameras have used a technology called CVBS (composite video baseband signal). This is the same technology that you will have seen in the past on devices such as DVD players. CVBS has limitations as to the resolution that it can transmit, typically this is around 480i.

For years, the world has come to see ever increasingly high-definition cameras get developed.  Until recently we haven’t seen this trickle down to things like reversing cameras.

The reason for this delay is due to the problems in transmitting high-definition video across distances greater than a few meters. Digital video signal cables are limited to short distances without the use of repeaters. For example, HDMI cable has not long advanced to be able to handle around 15ft before signal degradation becomes an issue.

AHD is known as Analogue High Definition; it allows a High-Definition video signal to travel through a traditional analogue coax cable. This new technology solves the transmission distance limitations issue and allows the reversing camera world to finally experience a substantial increase in both definition and dynamic range.

With it being a new technology, how can I be assured I won’t experience any teething problems?

The truth is that AHD has been around for a number of years now, and it DID have teething problems. This is why we only brought in our range in early 2022, once we were convinced it was stable enough.

We did bring some small batches of AHD kits a few years earlier, selling them cheaply to assess how they performed in the real world. For the most part they worked well, but they weren’t perfect. The biggest problem was something the factories termed “flicker”. In 2021 we were informed that this had finally been solved, and all of our samples / road tests confirmed this.

So are all AHD cameras better than the traditional cameras?

The short answer is no.

As always, the answer is more complex than just comparing numbers. For example, you can get 720P/960P/1080P camera chipsets for just a few quid (£). The cheap camera chipset will give you a worse picture than a good quality traditional CVBS 480i camera, despite its “bigger numbers”.

The only real way we were able to decide on which image sensors we would stock in our new range, was to test them out in the real world with lots of samples.

If the monitors aren’t also 1080P, then what is the point in using a 1080P camera?

Resolution isn’t a massive problem when it comes to the smaller screens used in reversing camera monitors eg 7 inch. The 800x480 (384,000 pixels) digital hi resolution panels used on our standard premium systems have pixels so small it is hard to see them, even close up! The only time we hear people mention resolution as a problem, is when discussing the cheaper analogue LCD panels that have 480x234 pixels (112,320 pixels) displays - these you can easily see pixels.

Our AHD monitors are upgraded to 1024x600 pixels (614,400 pixels), which is a 60% increase compared to the digital LCD. They also use IPS panels instead of standard LCD, which allows for better colour replication.

During testing we notice that some of the best AHD camera image sensors are 1080P only, such as the Sony IMX307 sensor. When you compare this sensor to cheaper 720P/960P/1080P AHD sensors, you see a big difference in night-time picture, as well as when there are differences in light levels across the picture eg. bright headlamps in an unlit area, or shadowy areas on a bright day.

So although you won’t experience full 1080P, when it comes to screen sizes that are substantially smaller than your TV at home, and a lot closer to your eyes, it isn’t really noticeable. Plus you get the main benefits of high dynamic range, great colour, and great low light level performance.

So are there any drawbacks to AHD?

Not many, the main one is the delay in changing channel – this is around 2-3 seconds on average, compared to approx. 1 second with traditional CVBS signal systems.

The second is that the night mode kicks in more suddenly. With traditional CVBS cameras the transition between night and day is much slower. AHD goes black and white as soon as the light level reaches a certain Lux level. Most of our AHD cameras this happens at between 1 and 8 Lux depending on camera model. In night mode the camera image will be black and white, with no colour visible. This has advantages though, since the black and white image will be miles more detailed than a colour image with a lot of “noise” to the picture.

Is there any point in selling the CVBS technology still?

Absolutely, CVBS reversing cameras will still be around for many years to come.

When it comes to car stereos, there are only a few models that can support AHD, the vast majority will only support CVBS.

When it comes to full systems, people will appreciate the cheaper cost, the quicker start up/changeover times, and still appreciate the good image quality that our premium CVBS sensors give.

Our summary

As you can see, things are never as simple as they first appear. All we can ask, is that you trust our judgement when it comes to image sensor choice/quality. Leave it to us to road test hundreds of variations, both day and night, before bringing the best to market (working with the factories to improve their product with our experience).

I hope this bit of knowledge has helped inform your product choice.