Interesting tool showing the relationship between FOV, Distance and Recognition

[c4rc4m]

Found an interesting tool quite by accident, that's meant for CCTV use (to enable you to select the correct camera and lens for your needs).

We've had many a discussion on here about this (a few heated ), so I found this interesting as it shows the relationship between Resolution, FOV, Distance, Readability of number plates (it has a guy holding a numberplate and simulates the blur (presumably based on a series of real life pictures) at different distances / resolutions, FOV's, as well as showing a picture simulating the FOV for any given lens:

https://calculator.ipvm.com/

Click add a camera to get going then have a play.

In my experiments with the tool, a 1080P camera at 20 feet, couldn't read a number plate satisfactorily with more than a 90 degree lens.

This may confirm some of the discussion we've had in the past and may also explain why so many of us struggle to read plates given that the average 1080P dashcam has a lens @140 degrees or more.

 

[Nigel]

Note that it says Horizontal Field of View, most of our camera specifications are diagonal FoV.

It nicely shows that a 4K camera sees the number plate in the same detail at twice the distance.
Pity it doesn't simulate the effect of motion blur and sensor sensitivity so that we can compare the 1080 at 1x distance and 4K at 2x distance to see which is the better choice in real life.

 

[boilers]

Best post in YEARS!!!!!

 

[SawMaster]

A very nice find and I'm bookmarking this as I know it will be handy in the future

Phil

 

[c4rc4m]

Note that it says Horizontal Field of View, most of our camera specifications are diagonal FoV.

Probably need to convert then. This appears to be a quirk of the dashcam market as CCTV lens are specified in horizontal and I'm pretty sure camera lenses are - maybe this is because the Chinese wanted their camera lenses to appear wider than they really were, due to the cost of quality wide angle lenses?

I'm sure there must be a converter somewhere to allow us to calculate the difference.

It's also worth remembering that for recognisability, the recommendation is for 500 pixels horizontally across the width of a face.

It nicely shows that a 4K camera sees the number plate in the same detail at twice the distance.
Pity it doesn't simulate the effect of motion blur and sensor sensitivity so that we can compare the 1080 at 1x distance and 4K at 2x distance to see which is the better choice in real life.

That is explained by the last sentence of my previous answer. 4K is a big step up in pixels from HD - 2mp vs 8mp. As a result at any given distance / width the pixel density is greater.

As for motion blur, that's down a lot to compression in my opinion with some aberrations down to shutter type / function. Where you have movement, there's a lot changing in the frame and so the picture is going to be compressed harder which means more loss of detail.

Sensor sensitivity, is down to the individual sensor. The ideal would probably be an 8K Sony STARVIS sensor, and these do exist in Sony's inventory. However, atm they're not really even finding their way into CCTV which suggests they're way to expensive to integrate. No doubt that will change over time. Of course the Holy grail would be the sensor used in Sony's A7IIS camera as it produces an almost perfect picture at as low as ISO 250,000 (!!!). However, the sensor cost and the fact that it's 1 inch in size and thus the lens cost, probably rule it out of car use for some time, which is a pity as it's the ultimate solution to nightime.

 

[jokiin]

Probably need to convert then. This appears to be a quirk of the dashcam market as CCTV lens are specified in horizontal and I'm pretty sure camera lenses are - maybe this is because the Chinese wanted their camera lenses to appear wider than they really were, due to the cost of quality wide angle lenses?
.

I got attacked last time I mentioned it as though it was somehow my fault but you'll find that the majority of brands out there don't give any sort of accurate details about the viewing angle of their lenses so using the numbers provided unfortunately is not going to be reliable in the majority of cases

 

[Nigel]

Lenses don't actually have a horizontal FOV since they are round! The horizontal FOV will depend on the aspect ratio you use, at 16:9 you get more horizontal FOV than at 4:3.

Of course the Holy grail would be the sensor used in Sony's A7IIS camera as it produces an almost perfect picture at as low as ISO 250,000 (!!!). However, the sensor cost and the fact that it's 1 inch in size...

The A7 range use full frame sensors, you will never use one of those in a dashcam.

 

[c4rc4m]

I got attacked last time I mentioned it as though it was somehow my fault but you'll find that the majority of brands out there don't give any sort of accurate details about the viewing angle of their lenses so using the numbers provided unfortunately is not going to be reliable in the majority of cases

Presumably not by me as apart from a bit of verbal sparring with a certain US member, in which even then I stayed polite, I'm not one to attack anybody. If you feel I have been harsh in my words towards you at any point, I apologise.

Lenses don't actually have a horizontal FOV since they are round! The horizontal FOV will depend on the aspect ratio you use, at 16:9 you get more horizontal FOV than at 4:3.

I think the shape of the lens is irrelevant Nigel. If we're going to pick hairs, on that reasoning, you can't have a diagonal fov because a circle doesn't have corners! Of course in reality, we're talking about the final image on the square sensor, and not the lens! The horizontal FOV is simply how wide the picture is and easily measurable. Personally, I've only ever seen CCTV and stills / video camera lenses expressed as horizontal measurements. Even the Wiki seems to suggest that horizontal or vertical is the more usual method of calculation (bottom of their calculation example):

https://en.wikipedia.org/wiki/Angle_of_view

Interestingly though, they do publish a table of common fixed focal lengths vs horizontal, vertical and diagonal fov's. As I suspected, the diagonal fov is wider than horizontal, which makes me suspect that maybe diagonal has be used for marketing purposes with dashcams as it's a higher figure so makes lenses look more impressive.

The A7 range use full frame sensors, you will never use one of those in a dashcam.

I agree although, I can't see any reason why one couldn't be used other than cost. You certainly wouldn't fit one in a Mobius or Runcam though for example! Size wise, I'm guessing the camera would be more in the range of one of the larger models of dashcam. I believe in Sony's list of sensors, there is a similar high sensitivity sensor in a smaller format. I'm guessing the current issue though is cost.

 

[c4rc4m]

I just found a diagonal fov conversion table here:

http://vrguy.blogspot.co.uk/2013/04/converting-diagonal-field-of-view-and.html

 

[jokiin]

If you feel I have been harsh in my words towards you at any point, I apologise.
.

no never, nothing to apologise for I can assure you

as I mentioned previously the greater majority of product out there do not offer any kind of accurate numbers or details on their lenses, some maybe intentionally, some maybe not, what is very typical is they quote the maximum numbers the lens supports, you'll see lots of products out there that claim to have 170° lenses with no real detail of what that number is supposed to be about (bigger numbers must be better when it comes to marketing though right) but the reality is most of these types of products are offering about 115° to 120° of horizontal viewing angle, in their online advertising they often have fancy graphics of cars showing a 170° view drawn out to show an almost edge to edge view which is nowhere near the truth

what is typical from Chinese lens suppliers is they'll offer a lens with a spec sheet that says something like 170° max diagonal view then it will list a bunch of different CMOS sensors and what the viewing angle is with each sensor, average Chinese seller just picks the biggest number (remember big numbers are better) and quote that in their spec list, some aren't even that accurate, some just quote whatever is printed on the generic public box that they buy from the packaging factory that they put their camera in and it may have no connection to whatever lens they use at all, pretty much the whole bottom end of the market is done like this

as an example the lens we used on the V1 and V2 GC was quoted by the manufacturer as being a 165° lens, the actual results when used with the IMX322 sensor was 112° horizontal, (it was measured independently at 111° horizontal), I have no doubt if anyone else was using the same lens they would have been promoting it as a 165° lens, it's just the way they do things unfortunately

 

[Dashmellow]

I got attacked last time I mentioned it as though it was somehow my fault but you'll find that the majority of brands out there don't give any sort of accurate details about the viewing angle of their lenses so using the numbers provided unfortunately is not going to be reliable in the majority of cases

The "discussion", that you characterize as an "attack" was specifically about the fact that most dash cam manufacturers including Street Guardian refuse to provide the focal length of the lenses in their cameras, unlike most any other true camera on the market such as CCTV cams which always provide this data. The specific "viewing angle" (FOV) provided by any given camera is a somewhat separate issue from focal length as it can be influenced by other factors. Significantly, the online tool provided by @c4rc4m has a required input field for focal length, thus rendering it useless for analyzing most dash cams.

To quote from the Wikipedia provided link on "Angle of View":

"The effective focal length and the image format dimensions completely define the angle of view."

Without that key piece of information regarding focal length anyone interested in making an informed decision is in the dark.

 

[Nigel]

"The effective focal length and the image format dimensions completely define the angle of view."

When buying a dashcam, I want to know if it is 360 degree (full view around the car), 180 degree(just half the view around the car thus requiring a 2nd rear view one), 90 degree (just covers the view in front) etc.

If we are buying based on the "effective focal length", what focal length do I want for a 360 degree view? To work it out I will need to know how big the sensors are, how many sensors, how much overlap between sensors for stitching, how much is cropped for EIS etc!

Much easier to stick with horizontal field of view which everyone can easily understand

 

[Dashmellow]

When buying a dashcam, I want to know if it is 360 degree (full view around the car), 180 degree(just half the view around the car thus requiring a 2nd rear view one), 90 degree (just covers the view in front) etc.

If we are buying based on the "effective focal length", what focal length do I want for a 360 degree view? To work it out I will need to know how big the sensors are, how many sensors, how much overlap between sensors for stitching, how much is cropped for EIS etc!

Much easier to stick with horizontal field of view which everyone can easily understand

When buying any camera or lens, I wish to know the focal length. This is particularly important if you are selecting an alternative lens for a camera such as the Mobius. Not everything revolves necessarily around dash cameras, per se. Knowing the focal length of a lens provides a point of reference in making a lens purchasing decision even if there are other factors involved, as stated above. There is also far more involved than your notion of "view around the car". Many buyers are interested in a more telephoto effect to better capture details of the vehicles in front of you such as plate numbers.

 

[Nigel]

Many buyers are interested in a more telephoto effect to better capture details of the vehicles in front of you such as plate numbers.

Again, the focal length does not tell you how detailed a number plate will be since you also need to know the resolution of the sensor and the size of the sensor. The important measure for reading number plates is pixels per degree which would be useful to have in the specifications, although you can work it out fairly easily if you have the horizontal field of view and horizontal resolution of the image.

 

[Dashmellow]

Again, the focal length does not tell you how detailed a number plate will be since you also need to know the resolution of the sensor and the size of the sensor. The important measure for reading number plates is pixels per degree which would be useful to have in the specifications, although you can work it out fairly easily if you have the horizontal field of view and horizontal resolution of the image.

I find it bizarre that anyone having a serious interest in any type of camera would advocate for not informing the consumer of the focal length of the lens installed. This kind of logic on your part Nigel is merely rationalization.

As for knowing how detailed a number plate will be according to the focal length, why not have a look at some of interesting recent work some of us have done installing longer lenses in the Mobius and other cameras.