Resolution verses field of view

[shockwave199 0]

I had this thought mainly pertaining to what a court would legally accept as positive ID. This does pertain to an install I have coming up at the front door of a commercial building for a family member. The dahua 2MP mini dome is perfect for the location. However, the lens is a 3.6mm. I don't wish to try another lens size in the camera- I want it stock so as not to fuss. The 3.6mm lens at 2MP will indeed capture excellent, detailed images of people when they get in the sweet spot to do so. But as we know, a 3.6 is pretty wide and there may be other people needed for ID outside of the sweet spot, but still prefectly ID'able if you drill into a snap shot from the original full image. Maybe even a vehicle or plate number. But by drilling into a shot, you lose time/day stamp- the very thing you need to prove the suspect was in fact there on that day and at that time. So all of a sudden, high resolution with the ability to drill into a shot for ID because you have more detail seems to lose it's power with wide shots. So with that thought and keeping in mind what a court of law would dictate, even with a high res MP picture, is it still important to provide positive ID with time/day stamp in the shot? If so, field of view is still critical even though a wide shot provides more coverage at high resolution for drilling.

 

The other thing to consider is that a good NVR or perhaps even the camera, if it's recording to a micro card, should have the option to embed a digital watermark [signature] with that critical information no matter what you drill into for ID, correct? But that's not really specified in most spec information when you're shopping an NVR, and I've only come across one DVR that we use at work that has the option. Normally most people assume the time/date stamp on the shot with positive ID is what they'll need in court. What happens if you drill in and can get positive ID, but you lose the time/date stamp?

 

We always talk about the wonderful high res pictures MP provides even with wide shots, but isn't the appropriate field of view for proof of positive ID with time/date stamp on the image still critical?

[thewireguys 3]

You just gave me another reason not to use Dahua

 

This is not an issue with our VMS solutions and I suspect most if not all main stream VMS solutions.

[shockwave199 0]

Well, I don't know if it's lacking in a dahua NVR or camera. I guess I'll have to start reading manuals.

 

[gilligan 0]

I think I'm missing something.

 

Are you "drilling" into this image POST capture?

 

If so then why are you losing the time stamp, put the images side by side or blow them up from the wide in an "animation".

 

If this is blown up during capture (a digital zoom) then you are certainly going about things the wrong way and should do things the right way and get the proper lens (equipment) for the task.

 

Btw, you can order the camera with different lenses most of the time.

 

This brings up a question to TheWireGuys, why are you faulting the manufacture because the end user is seemingly using the gear improperly or at least out of it's scope.

[dexterash 0]

IMHO, a timestamp on a recording isn't a "secure" thing, as the clock can be changed by anyone (or did I get the picture wrong?).

 

All of the DAHUA's recording devices use a digital watermark on their recording (a CRC) that can be checked via the dedicated player (we are talking here about the .DAV file that is downloaded from the device)

 

Also, the player has the capability to pause&save a snapshot if you want to digitally zoom it.

Edited March 25, 2013 by Guest

[gilligan 0]

Speaking of, my cameras are displaying one time and my NVR time log is an hour off (need to look into that after I hit send).

[dexterash 0]

Use a NTP - time server to keep the devices in sync (I do remember an option on DAHUA's NVR to auto-sync it's time with camera)

[quanganh904 0]

i think camera ip better camera antalog

[mobbarley 0]

AXIS have a pretty good write up on resolution - it's not a legal standard but an adaption of older analog standards. http://www.axis.com/files/feature_articles/ar_perfect_pixel_count_47927_en_1212_lo.pdf

 

'Pixel density' is a good measure of usable resolution but you still have to consider the usability of the image, eg: are details clear & sharp etc.

 

To measure: put a ruler in the picture at the desired distance, take a snapshot, count the pixels and multiply to find pixels per foot / meter..

[MaxIcon 0]

Really, it boils down to one thing (in the US, at least) - does the image allow identification of a suspect beyond reasonable doubt? For instance, could you tell the difference between two similar looking people standing next to each other in an image? That actually takes pretty good resolution and clarity, and low compression.

[fenderman 0]

I had this thought mainly pertaining to what a court would legally accept as positive ID. This does pertain to an install I have coming up at the front door of a commercial building for a family member. The dahua 2MP mini dome is perfect for the location. However, the lens is a 3.6mm. I don't wish to try another lens size in the camera- I want it stock so as not to fuss. The 3.6mm lens at 2MP will indeed capture excellent, detailed images of people when they get in the sweet spot to do so. But as we know, a 3.6 is pretty wide and there may be other people needed for ID outside of the sweet spot, but still prefectly ID'able if you drill into a snap shot from the original full image. Maybe even a vehicle or plate number. But by drilling into a shot, you lose time/day stamp- the very thing you need to prove the suspect was in fact there on that day and at that time. So all of a sudden, high resolution with the ability to drill into a shot for ID because you have more detail seems to lose it's power with wide shots. So with that thought and keeping in mind what a court of law would dictate, even with a high res MP picture, is it still important to provide positive ID with time/day stamp in the shot? If so, field of view is still critical even though a wide shot provides more coverage at high resolution for drilling.

 

The other thing to consider is that a good NVR or perhaps even the camera, if it's recording to a micro card, should have the option to embed a digital watermark [signature] with that critical information no matter what you drill into for ID, correct? But that's not really specified in most spec information when you're shopping an NVR, and I've only come across one DVR that we use at work that has the option. Normally most people assume the time/date stamp on the shot with positive ID is what they'll need in court. What happens if you drill in and can get positive ID, but you lose the time/date stamp?

 

We always talk about the wonderful high res pictures MP provides even with wide shots, but isn't the appropriate field of view for proof of positive ID with time/date stamp on the image still critical?

As mentioned the time stamp is not secure. That being said, the rules of evidence in most states requires that the person proffering the evidence authenticate it. That means, that either the security person or owner of the NVR, or a victim who was present when the footage was taken authenticate and state when the video was captured. You don't need a time stamp at all. With respect to the image its a judge or jury's call whether the deem the quality appropriate to convict.