Overexposed License Plates with LED Headlights

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kinglerch

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I have a new Street Guardian Dash Cam SGGCX2 and although the image quality is great, my LED headlights are normally so bright that I never use my highbeams. On the dash cam, when the license plates pass just out of the headlight area the letters are legible but within the headlight area they are just about all stark white. The only thing I can think to try is gradually reducing the EV. Is there another way or a recommended EV setting?

The Street Guardian, although a great camera has a very average manual. The options for things like AE Metering are not described, and I don't know if WDR would help or hurt this issue. The unit did include a CPL filter, though I don't think it would affect this issue.

Thanks for the help.
 
All dashcams suffer from this, there's not much you can do. You'd suffer the same problem with Halogen and HID headlights as well.
 
Welcome to DCT, @kinglerch!

If you had posted this thread in the SGGCX2 sub-forum your questions would probably be addressed by now. Here in the General Dash Cam Discussion it will be harder for @jokiin or @Street Guardian USA to find it but don't worry, the tags will call their attention. :)
 
kinglerch said:
I have a new Street Guardian Dash Cam SGGCX2 and although the image quality is great, my LED headlights are normally so bright that I never use my highbeams. On the dash cam, when the license plates pass just out of the headlight area the letters are legible but within the headlight area they are just about all stark white. The only thing I can think to try is gradually reducing the EV. Is there another way or a recommended EV setting?

The Street Guardian, although a great camera has a very average manual. The options for things like AE Metering are not described, and I don't know if WDR would help or hurt this issue. The unit did include a CPL filter, though I don't think it would affect this issue.

Thanks for the help.
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you could have a play around with the EV setting but that's going to have an affect on overall picture, not just licence plates, so you need to assess that carefully, all cameras will have this same effect with licence plates, there are some threads here that @niko posted previously that cover the effects of headlights and EV settings
 
I posted the message here since I thought it was a more general issue, rather than specific to the Street Guardian. The thread I read seemed to say that EV -2 helps but kind of ruins the rest of the picture. I set my EV to -1 hoping it would help but despite the entire picture being darker, do you think the EV reduction will even work or is the contrast between the darkness and bright plate insurmountable?
 
Try lowering the cut-off on the LED headlights.

I have retrofitted HID's in my car, lowering the throw helps with plates on hatchbacks and low slung sedans.
 
kinglerch said:
...is the contrast between the darkness and bright plate insurmountable?
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That pretty much describes the situation - regardless of what camera. It's exascerbated by that fact that a lot of plates have some sort of reflective material incorporated which makes that matter even worse. :(
 
Plates are retroreflective so they are almost as bright as the actual headlight! No way to get around that except by having the camera be significantly offset, maybe up on some kind of pole atop the vehicle
 
I just thought of an idea though... Get a narrow angle camera (see the Mobius telephoto thread) and modify it to capture only infrared light. Then affix an infrared illuminator to your car. The combination of the two may get you readable plates
 
jackalopephoto said:
I just thought of an idea though... Get a narrow angle camera (see the Mobius telephoto thread) and modify it to capture only infrared light. Then affix an infrared illuminator to your car. The combination of the two may get you readable plates
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We previously discussed the idea of using an IR Mobius with an IR Illuminator and it's an interesting idea worth exploring for improved dash cam night vision but from my experience it won't work any better to capture license plates as long as your bright headlights are blowing out all the highlights. If the reflections coming off the plates exceed the dynamic range of the camera and blowing out the upper end of the tonal range, it doesn't matter which wavelengths of light it's capturing as all you'll see is a bright white rectangle. In my IR experiments some license plates did get captured better than others depending upon the colors of the plates. Certain colors absorb or reflect IR light better than others. I think the idea might work if the camera was set to ONLY expose for the brightly lit plates.
 
Dashmellow said:
We previously discussed the idea of using an IR Mobius with an IR Illuminator and it's an interesting idea worth exploring for improved dash cam night vision but from my experience it won't work any better to capture license plates as long as your bright headlights are blowing out all the highlights. If the reflections coming off the plates exceed the dynamic range of the camera and blowing out the upper end of the tonal range, it doesn't matter which wavelengths of light it's capturing as all you'll see is a bright white rectangle. In my IR experiments some license plates did get captured better than others depending upon the colors of the plates. Certain colors absorb or reflect IR light better than others. I think the idea might work if the camera was set to ONLY expose for the brightly lit plates.
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If the camera has a visible light blocking filter so it only sees IR, that would cut all light from LED headlights. Incandescent lights not so much, so there probably wouldn't be any benefit. Not sure about xenon

What's good about the telephoto is you can maximize exposure for plates, whether it's IR or just your headlights. Your regular dashcams have to be bright enough to capture cars
 
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The only other option I could think of would be for the camera to detect a white light (or bright area) and reduce the exposure (aperture?) until the bright area is within acceptable limits. IMO, the biggest issue is that although license plates are certainly useful and important pieces to the puzzle, even if the camera could adjust to read them, if it comes at the expense of seeing any meaningful activity (i.e. the accident itself) then it would be pointless. I have a high end camera that could read the plates, but likely only when zoomed in and not in an otherwise dark frame. To get an overall decent picture of what is happening in the dark, it could only come at the expense of some blown out areas.
 
jackalopephoto said:
If the camera has a visible light blocking filter so it only sees IR, that would cut all light from LED headlights. Incandescent lights not so much, so there probably wouldn't be any benefit. Not sure about xenon

What's good about the telephoto is you can maximize exposure for plates, whether it's IR or just your headlights. Your regular dashcams have to be bright enough to capture cars
Click to expand...

Well, the thing with telephoto lenses on dash cams is you have to hope the plate you wish to capture happens to be in the frame. Sometimes the problem car you need to capture is in another lane of traffic.

A visible light blocking filter might be worth experimenting with except that they tend to be very pricey, possibly costing as much as a Mobius or more. IR illuminators with enough output are not cheap either. The one posted to the IR varifocal thread is over a hundred bucks. That's the problem with some of these experimental ideas. They might ultimately be worth the investment in the required equipment if it all works but if it doesn't you got a useless IR illuminator and filter.
 
Dashmellow said:
Sometimes the problem car you need to capture is in another lane of traffic.
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off axis you can generally catch with most cameras already, less of a problem to begin with

the stuff directly in front is the big problem, very hard to have an effective solution for this I would think
 
jokiin said:
off axis you can generally catch with most cameras already, less of a problem to begin with

the stuff directly in front is the big problem, very hard to have an effective solution for this I would think
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I get what you are saying, except that I've certainly experienced cars in other lanes with blown out license plates. Often the plates of cars in the adjacent lane are over-illuminated by the car behind them.
 
Mini 0805 on centre-spot does what kinglerch mentioned, but yes everything else goes too dark.
 
Dashmellow said:
I get what you are saying, except that I've certainly experienced cars in other lanes with blown out license plates. Often the plates of cars in the adjacent lane are over-illuminated by the car behind them.
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that's a possibility although still less of a problem, sure there could be frames of video where it blows out but plenty of frames where you will get the plate, viewed off axis the reflection issue is much less of a problem
 
vb
jokiin said:
that's a possibility although still less of a problem, sure there could be frames of video where it blows out but plenty of frames where you will get the plate, viewed off axis the reflection issue is much less of a problem
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The concept that "there could be frames of video where it blows out but plenty of frames where you will get the plate" also applies to cars directly in front of you. Sure, when your own headlights are blasting plates in front of you they will get blown out on video but reflections are actually based on the "angle of incidence". The reflective paint on the plates changes the equation somewhat but doesn't eliminate the laws of physics.

reflections.jpg

I know we would all like to capture clear images of the brightly illuminated license plates of the cars directly in front of us and that's a worthy goal but if you stop to think about it, when accidents happen that's often not the angle the car is coming at us from unless they've slammed on their brakes.
 
Yeah I don't see it as a deal breaker, it's not like it's never possible to catch a plate, it's like people that worry that they can't see a plate that's 100m further ahead, not often you get hit by something from 100m away
 
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