Poor IR contrast in new Tennessee license plates

[wtimothyholman]

I'm guessing the same way that a piddly led flashlight can reflect off a sign that far away but clearly isn't providing enough light to be effective at that distance.

I guess we need to investigate the IR on cameras because from the street the red glow of a bullet looks the same as that of a turret,but the bullet range is further. Is it strictly a wattage thing or is there something we are missing that is flawing the 730nm option.

Probably wouldn't make a difference, but what about b/w with I think it is called the electrical option (I think it is electrical and ICF or something like that as two options) and see if that picks it up?

Or if you can see the red reflection, what about adjusting the red on the color balance?

Just brainstorming ideas to try to make it work.

Color balance won't have any effect; the camera is in B/W mode. I've already tried adjusting that previously with no effect.

My best guess at this point is that the beam angle from the IR LEDs needs to be much narrower. Consider that in a bullet camera the LEDs will point in the same direction as the lens, so precise alignment with a narrow beam angle is automatic. I'm now wondering if I should have specified 10 degrees instead of 30 degrees. Yet professional illuminators provide a wide range of available beam angles at similar power levels. So ... do professional illuminators use different IR diode emitters?

 

[The Automation Guy]

I think the camera's IR filter also plays a role here. The cameras are designed for 850mm IR, not 730mm. This means that while the camera can pick up some of the 730mm IR, it is likely being reduced by the IR filter.

 

[handinpalm]

I think the camera's IR filter also plays a role here. The cameras are designed for 850mm IR, not 730mm. This means that while the camera can pick up some of the 730mm IR, it is likely being reduced by the IR filter.

The IR filter is used to filter IR band in the Color mode. In the night mode, or B/W mode, the IR filter is switched out, so this is an incorrect statement.

 

[The Automation Guy]

The IR filter is used to filter IR band in the Color mode. In the night mode, or B/W mode, the IR filter is switched out, so this is an incorrect statement.

Thanks for the correction!

 

[sebastiantombs]

I'm just wondering if the optics, themselves, may be filtering at 850nm given the poor results at 750nm. That would seem to be the only other way, or variable, in the equation.

 

[wittaj]

On your PTZ, try the electrical setting and see if that improves the image with the 740nm

 

[wtimothyholman]

On your PTZ, try the electrical setting and see if that improves the image with the 740nm

View attachment 120509

I'll try it, but I doubt it will have any effect. The IR cut filter was already in "off" mode, so electrical compensation wouldn't matter.

 

[wittaj]

I am just brainstorming ways to test different things to try to make this work.

I guess swinging for the fences did you try it in color? Maybe as @sebastiantombs suggests there is something with the sensor or coating or IR filter that would make this visible in color?

I just think if we try everything, we can either figure out what works or conclude that this bulb just simply doesn't have the distance range needed.

 

[wtimothyholman]

I'm just wondering if the optics, themselves, may be filtering at 850nm given the poor results at 750nm. That would seem to be the only other way, or variable, in the equation.

I think the missing variable is the 730nm bulb itself. I have no idea of its emission efficiency, or the quality of its output spectrum. Yes, it's a 7 watt bulb, but it may actually be far less efficient at 730nm than the lower power 850nm LEDs in the camera.

I'm going to gamble another $20 and get a higher power bulb, and go all out on the next test. Maybe the bulb will be too bright in the visible spectrum for long-term deployment, but at least I'll have an idea if it can be made to work.

 

[handinpalm]

I do not know how far off center the 730nm light is from your camera location, but I think you will find that you will get maximum reflection when the external light is right in line with the camera, ie right next to it, or in the same line of sight to the target.

 

[wtimothyholman]

I do not know how far off center the 730nm light is from your camera location, but I think you will find that you will get maximum reflection when the external light is right in line with the camera, ie right next to it, or in the same line to the target.

That is an excellent point. Direct normal reflection back into the camera may be absolutely essential. The temporary fixture I was using for my tests was about four feet to the side from my cameras. Yes, I was able to "aim" the lamp, but the key to making it work may be a direct line-of-sight reflection into the camera lens.

I'll try that tonight with the PTZ camera, and if I get better results I will try it with an LPR camera.

 

[handinpalm]

Manufactures (3M) design their reflective material for max reflection from a light when something is in its light of sight, or behind it, because that where it matters. The old reflective street signs use to use glass beads for this purpose. Look at the refraction properties of a glass bead. Ever wonder how the pavement stripping on roads reflect the headlights so well when you are in the car behind the light, but does not look that reflective if you are standing off the side of the road when a car goes by? They still use glass beads in the paint (pavement markings) for reflection.

 

[wtimothyholman]

Manufactures (3M) design their reflective material for max reflection from a light when something is in its light of sight, or behind it, because that where it matters. The old reflective street signs use to use glass beads for this purpose. Look at the refraction properties of a glass bead. Ever wonder how the pavement stripping on roads reflect the headlights so well when you are in the car behind the light, but does not look that reflective if you are standing off the side of the road when a car goes by? They still use glass beads in the paint for reflection.

You're absolutely right. Now I'm getting hopeful again that I may be able to make this work. Some more experimentation is in order.

 

[wtimothyholman]

Tonight I performed some more experiments, and can only come to one very surprising conclusion: the Dahua IPC-HFW5231E-Z12 camera is insensitive to 730nm infrared light.

The Dahua SD49225T-HN PTZ camera does respond to 730nm light. I confirmed this by turning off the internal IR while leaving the camera in B/W mode, and using the bulb to illuminate the scene. I then used the same shutter, gain, and iris settings on the PTZ as I do for the -Z12 in LPR mode, and again confirmed that the camera responded to 730nm IR.

But the -Z12? Nothing. After multiple failed attempts to get some sort of image from a license plate positioned directly in the camera's field of view while using the 730nm bulb, I had an idea. Using an extension cord, I walked into the yard and pointed the 730nm LED bulb directly at the LPR camera. The result? Nothing. By contrast, doing the same thing with an 850nm illuminator provided a very visible bright flare in the camera view. As for the PTZ camera, it responded both to 850nm and 730nm illumination.

I am both surprised and puzzled by this development. How is it that a camera that is so sensitive to 850nm IR can be essentially blind to 730nm IR, particularly when the IR cut filter is not in use? So while I've learned something quite interesting about the "go to" camera that most of us use for LPR, I also know that my goal to add 730nm illumination to my LPR system is simply not going to work.

 

[bp2008]

Wow. Is 740nm is barely into the infrared spectrum and practically nothing uses it. Who would ever decide to design license plates for reflectivity in that wavelength?? Your tax dollars at work.

I have to imagine the red glow is substantially stronger for equivalent output power due to being so much closer to just plain "red" compared to 850nm.

 

[bp2008]

At this point I'm a bit puzzled. The power output of the 730nm bulb should be comparable or greater than the power output of the 850nm LEDs in the cameras, and if anything the sensors should be more sensitive to the longer wavelength IR. Yet overall performance is much worse.

730nm is the shorter wavelength, not longer.

I'm just wondering if the optics, themselves, may be filtering at 850nm given the poor results at 750nm. That would seem to be the only other way, or variable, in the equation.

Yeah. Without knowing a lot more about the materials used in the lens and the glass or plastic cover in front of the lens, you could be right, the light might not even be making it to the sensor. It is a shame that quality lab equipment to measure such things is quite expensive.

 

[wittaj]

That is crazy.

So I guess the test to try if possible is aim your PTZ to the street and set up as a plate reader and at distance does the bulb work and does it do a better job reading the new plates?

 

[wittaj]

@Wildcat_1 any thoughts on why the Z12E cannot see 730nm but the 49225 can?

 

[wtimothyholman]

Wow. Is 740nm is barely into the infrared spectrum and practically nothing uses it. Who would ever decide to design license plates for reflectivity in that wavelength?? Your tax dollars at work.

I have to imagine the red glow is substantially stronger for equivalent output power due to being so much closer to just plain "red" compared to 850nm.

The idea behind the use of 730nm or 740nm light is that the shorter wavelength does a better job of penetrating the window glass and getting an image of the occupant, assuming that matters to you. Also, a higher frequency light source enhances resolution of the image. The drawback is the visibility of the illuminator. The Gaussian distribution of the LED’s spectral output means that it is very visible to the human eye. It’s not such a big deal for municipal deployment, but for home use it draws attention to itself at night.

The 740nm standard was considered a perfectly useable option a decade ago, when LPR deployment was limited to very expensive cameras. According to Skycop, Tennessee’s license plates were designed for 740nm viewing (which of course Skycop supported at the time). What no one foresaw was the explosion of 850nm LPR camera deployments over the past decade.

So now the question is whether Tennessee will change its plates to conform to 850nm visibility. The alternative is to push out 5.5 million plates by the end of 2022 that will be invisible to the overwhelming majority of LPR cameras at night. Flock Safety has 600 cameras deployed in the Memphis area alone, so this is turning into a major political mess.

 

[wtimothyholman]

That is crazy.

So I guess the test to try if possible is aim your PTZ to the street and set up as a plate reader and at distance does the bulb work and does it do a better job reading the new plates?

I might try that this weekend. I've used my PTZ as an LPR camera in a pinch before, and I just saw a video that compared 740nm and 850nm illumination for the new TN plates. The difference is pronounced. At 850nm, the plate is completely washed out (as I am seeing on my cameras), while at 740nm the contrast is normal. So it should work.

But ultimately the state of Tennessee needs to change the plates. Granted, the Department of Revenue could dig in its heels, but that means they'd be going against the overwhelming trend towards 850nm IR cameras that are cheaper, easier to deploy, and more covert. And it wouldn't just affect Tennessee, but every state around us. Skycop might be fine with that, but Flock Safety, Rekor, and Vigilant (among many others) aren't going to like it. There are probably thousands of Flock Safety cameras deployed in Tennessee alone.