Help me tweak my settings

[Robert G.]

I have been playing with ALPR for just over 1 year now.

Daytime shots are nice. I have two cameras, one pointing up the street the other pointing down. Using OpenALPR (or whatever it is called these days) so it can use the video feed from both cameras to come up with the best chance at getting the plate correct - which is a feature I really like.

Here are a couple of daytime shots.







Not perfectly straight on, the cameras are mounted under the roof overhang on a building. Both capture images 100+ ft. away from the camera.

Here is a night shot.




Most people would think that is quite good... What am I complaining about?

Stand by for my next posting where I show major 'issues' at night.

 

[wittaj]

Yep LOL that looks really good!

 

[Robert G.]

OK, seems like I am going to look a bit like an idiot here... Since the vehicles do not get captured, I not have photos of them.

My problem is capturing plates at night is not consistent. Here are three photos, taken just minutes apart.







The plate in the middle is very difficult to read. Why? The camera settings produced nice shots for the 1st and 3rd cars but the middle one is terrible.

I've thought of a few reasons why some plates do not reflect the light back:

1) They may be installed at an angle, pointing down or up a bit so the light does not shine back

2) The plates are very dirty, it is winter here to a lot of plates are covered in dirt which would kill the reflection of light

I would say I only catch about 50% of the vehicles at night. When my settings work, I get fairly nice shots like #1 and #3 above. But what about the ones I am missing?

 

[wittaj]

Yep - that happens. Not going to get every plate. Some plates will be dirty or have a film on them or a variety of issues.

You might also be experiencing a frequency issue - I have noticed that cars with all LED lights can pass by my camera and even though I can tell the lights are on from an overview cam and typical LED blinding, the camera is running at a FPS frequency such that it is catching it and making it look like your second image - notice the other side of the car lights are gone.

I also recognized that this winter when I put LED candles in our windows and even though they were solid on, the camera made it look like they were flickering. I adjusted FPS until it quit.

May fix yours or may not, but worth a try and then know if it were that or just bad plates.

 

[sebastiantombs]

I'm not an LPR expert by any means but I'd zoom in closer yet and maybe add some more IR (external IR illuminator or cannon). You didn't mention the model of camera.

 

[Robert G.]

The cameras in use are Dahua IPC-HFW5241E-Z12E.

I actually have two different IR illuminators already. They are both Axton PoE Illuminators, but with different angles for lighting. I bought one but did not find it was focused enough so I bought a second.

Here are a couple of photos of the area showing the IR lights, on and off. They do make a massive difference, unfortunately taking a photo seems to dumb down the light. It is actually more powerful than shows in the photo.

In playing with the IR light just now, I think it is pointing down too much. I'm not local to the install site, so I can't change it :-(

 

[sebastiantombs]

Assuming that you're pointing the IR in a line with the trash cans it does look like it's a little low. Raising it should help quite a bit. When you get there, I'd have someone either stand with a plate in their hands, at an appropriate height, or stop a vehicle there and set the IR that way rather than guessing. I use some strong IR floods and my guesses are usually wrong but YMMV.

 

[wittaj]

Are you running the IR on the Z12 at full 100 near and far? I am at 175 feet and no external IR and get all but the crappy ones fine.

 

[Robert G.]

@wittaj I have been running only the far at 100%. I have near @ 0%. Never found much difference with that on.

 

[Robert G.]

I have been messing with camera settings for a while. Seems like I have been able to improve the number of catches on one of the cameras.

My settings are totally contrary to what most people talk of on here.

One setting that puzzles me is Iris. I see most people on here suggest something in the 30 range. To me, the larger the Iris, the more light is allowed in. Does anyone know what the positives & negatives are of a larger or smaller Irus setting?

 

[samplenhold]

Does anyone know what the positives & negatives are of a larger or smaller Irus setting?

I've looked through the Dahua manual and it appears that the IRIS setting is similar to the aperture of an DLSR camera, aka F-stop. If this is true, then the setting is how much the lens opens. This will impact the exposure, larger opening = more light, smaller opening = less light hitting the sensor. The other impact is that of the depth of field. The smaller the aperture the deeper the depth of field. This means that the picture will be in focus over a greater distance range than if the aperture is bigger, yielding a shallower (aka thinner) depth of field.

I've adjusted this when it appears the some plates are out of focus and it has worked well for me.

 

[samplenhold]

Additionally, I have an overview cam that is in full color 24/7. I have looked at the plates that do not show up well on my LPR cams and have found most are in poor shape. Some are rear plates on trucks that have a trailer hitch at plate level and you can see that the plate has been hit several times by the trailer hitch so it is not flat, or the hitch ball is in the way and seems to scatter the IR light. Sometimes they are just dirty. Sometimes there is a plastic cover over the plate. Others have had the paint worn off. Some front plates that do not have a frame are bent or warped.