Member Discussion

Meeting Pixel Density Specificiations

I have read pretty much all of the discussions relating to pixel density, used the calculator and have generally determined what image requirements are for defined viewing levels (minimum). I have created a drawing schedule that lists each camera along with the pixel density at given target distances. A field of view and a description of the camera objectives (what I want to see), frame rates (on motion and alarm) and other items are also included on the schedule. The intent here is to basically create a performance-based criteria for each camera.

So, now that I have all this information to the integrator, how do I check it in the field once it's time for punch listing? Is there a tool for field checking the installation?

I am not disclosing my name because its a public bid and some of the integrators may be members of IPVM.

A few camera manufacturers have built-in pixel counters that simplify verification.

Here it is on an Axis camera:

And here it is with a Bosch camera:

That said, if the cameras do not have such a software based function, you can verify by measuring the FoV width at the target distance with a Laser Distance Finder. If the FoV width is correct and the camera has the right resolution, by definition you have the desired / specified PPF.

I can't spec an onboard ppf register, but i cannot be sure the winning integrator will supply a camera with that feature (I need at least five manufacturers). So lets talk about your second solution. Take a look at the attached corridor drawing which is very typical of about 500 cameras to be installed. I want to view the corridor for about 40 ft out (the pink area is where the subject starts walking out of the FoV). Lighting is fine and WDR is for another discussion. My FoV needs to cover the corridor and the door. At the door I have an ID level view of about 40 ppf (a bit low, but livable). However, when you extend the FoV out so the corridor can be adequately covered, the true field of view is 60 feet. Since you are in a corridor with walls and ceilings, how do you measure the field of view?

You want to specify the AoV then, i.e., 60° or whatever is appropriate.

The image did not post. Feel free to email me at and I'll upload it for you.

If you are specifying the ppf required, the camera resolution and the distance to target, the AoV is guaranteed. For example, if you specify 40ppf, 1080p camera and 40' distance to target, that requires a 62° AoV.

Solution is to specify the AoV as well (which is a direct outcome of what you are already specifying) and then verify AoV.

OK. Here is a couple of lines of my camera schedule. Thoughts?

You have AoV and pixel density, where is distance to target or resolution required? You'll need one of those 2 to make a complete specification.

The target information is shown after the ppf as distance (either a physical measurement or a specific object such as a door). My spec requires a minimum of 1.3 mp (you dont see that on the schedule. Probably should put it in as a general note). Using the IPVM calculator, a target 40' away with a 65 degree AoV using a 1.3 mp camera would result in 31.7 ppf image. Since my schedule calls for a 40ppm image at this location, the integrator would need to bump his camera selection up to a 2mp camera which would yield a PD of 38.4ppf, which is probably close enough.

"bump his camera selection up to a 2mp camera which would yield a PD of 38.4ppf, which is probably close enough."

Well, you are the consultant so it is you call to be explicit here. The integrator / responder does not know how strict you will be, so there may be some confusion here.

Agree. I have given some leeway on the locationing of the cameras, so the integrator should be able to move the camera or change the lens focal length to reach the target objective. I will keep it as is (min 40 ppf).

I am going to review the images with the owner this week to show him what the images look like at these various levels. What would be your recommendation for images that are representative of the various ppf values? The ones of Tony in the parking lot are pretty good and simple to understand. What are some others you would recommend? Maybe something interior. There are a number of sites out there, but there are some pretty significant differences between a number of them.