problems with automatic adjustment of IR backlight IPC-HFW7842H-Z

[Balex]

Hi guys!
I bought IPC-HFW7842H-Z cameras to replace my IPC-HFW2831T-ZAS-S2.
7842 work well during the day, but when switching to night mode, they are strongly illuminated by the IR spotlight, and it is impossible to recognize license plates.
The 2831 has face priority features in the IR illuminator settings, and they do a good job of reducing the backlight of people and license plates.
Tell me how this can be fixed? maybe I'm not configuring 7842 correctly?
same problem on my 5842 which i bought instead of 2831 installed inside the yard.

 

[wittaj]

The problem is you are not running a fast enough shutter. Smart IR, or the face priority features you mention won't help either.

At night, we have to run a very fast shutter speed (1/2,000) and in B/W with IR and the image will be black. All you will see are head/tail lights and the plate. We are taking advantage of the reflective properties of the plate. Some people can get away with color if they have enough street lights, but most of us cannot. Here is a representative sample of plates I get at night of vehicles traveling about 45MPH at 175 feet from my 2MP camera (that is all that is needed for plates):



So go in and change your shutter speed to a min of 1/1000. If it is a driveway you might be able to get by at 1/500. But it is the shutter speed you need to adjust.

Also, keep in mind that this is a camera dedicated to plates and not an overview camera also. It is as much an art as it is a science. You will need two cameras. For LPR we need to zoom in tight to make the plate as large as possible. For most of us, all you see is the not much more than a vehicle in the entire frame. Now maybe in the right location during the day it might be able to see some other things, but not at night.

So I would zoom in a little more as well.

 

[Balex]

I have a slow road, 5-15 miles per hour, and the camera is in metadata mode, the pictures on 7842 and 2831 were taken at the same time, with an increase in traffic 2831 the number is clearly visible, and in 7842 the whole car is illuminated.

 

[looney2ns]

You need to increase the shutter speed as others have mentioned.

 

[Balex]

why at the same speed you can see well at 2831, but only a flash is visible at 7842?

in the photo below there are two pictures at the same time and from the same angle, at 2842 you can see the number perfectly, and at 7842 there is a flash, only 2831 itself became darker, and 7842 did not change the brightness and a flash turned out

 

[wittaj]

The 2842 has a bigger sensor for one.

Different field of view is another - one is zoomed in tighter than the other.

Settings in the camera is yet another.

You are not comparing apples. Something is different in the one than the other. Increase the shutter speed and be amazed at the plates you capture.

 

[Balex]

2831 has a longer shutter than 7842. but everything is visible on 2831, but not on 7842.

 

[wittaj]

Different sensors do different things, along with settings of other parameters.

Quit fighting it and make the shutter faster LOL.

 

[Balex]

I made the shutter 1/1000, now it is very hard to see and the black bars move from top to bottom

 

[wittaj]

That is anti-flicker - turn it off or adjust the shutter until the flickering (moving black bars) disappear.

 

[Balex]

I can’t turn off Anti-flicker, you can choose 50 or 60 hertz, if you choose 50, then you can’t make the shutter more than 1/100, and if 60, then more than 1/120. Maybe I have an old firmware? on the dahua website, I did not find a newer System Version3.000.0000000.2.R, Build Date: 2021-07-12. maybe there is a firmware from Andy?

 

[wittaj]

Probably not a firmware issue. Given the vehicle speed and size of plates, I would suggest increasing and decreasing shutter speed to eliminate the flicker. Your lights are on the same frequency as the shutter speed. Trying 1/900 or 1/1100 will probably eliminate it.

There are some vehicles that come by that with their LED headlights, it looks like they are off because the light frequency is in tune with the shutter speed.