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Ask the Expert: How and when should I choose a megapixel camera?

In February, we tackled a similar topic by outlining Four factors to consider when selecting a megapixel camera. But because megapixel quality is the fastest growing segment among IP cameras, constant innovation continues to change the rules. Since rapid technology advancements can be confusing, let’s clarify the world of megapixel cameras even further.


June 16, 2010
By Robert Moore

Topics

More about lenses

We previously touched upon selecting the appropriate lens based on pixel count and field of view – but there is more to the lens story. Simply put: A badly matched lens will result in a poor image, regardless of how good the camera is. This is especially evident when zooming digitally.

Manufacturers have confused the market by saying their lenses are megapixel capable, without specifying the megapixel limit of the lens.  Most lenses will work well within the middle of the sensor, but aren’t strong enough to get the adequate amount of light to the entire sensor, especially the harder-to-reach areas around the edge. Obviously, light is crucial to reach the best image quality.

To ensure you have the right lens/camera match, check the number of lines per millimeter that the megapixel image sensor requires.  To make things easier (and help avoid mathematical formulas), lens manufacturers are now coming out with megapixel-rated lenses, so you can match a 3-megapixel lens with a 3-megapixel sensor.

Furthermore, a new lens technology, P-Iris, is also improving megapixel capabilities. It uses built-in software that calibrates the camera’s aperture opening for the best sharpness and exposure for the entire field of view.

One final note: Always field test! Even if you match the lens correctly and employ P-Iris, field test the camera to ensure you have adequate lighting and proper depth of field to get the image you expect.

Multi-streaming is here

The Holy Grail for megapixel is using one camera to provide several simultaneous views and record different video streams. Several manufacturers offer this capability and a growing number of software providers are coming onboard with the required solutions.

Here’s how it works: Imagine a shopping mall with a megapixel camera aimed down the main foyer. The megapixel camera streams one entire field of view of the mall floor, including retail entrances, kiosks and people walking by.  Using the VMS, security personnel can designate a smaller area within that field of view – say an entrance to a store often targeted by thieves – and simultaneously stream a second, zoomed in view to watch the storefront. It’s like having two cameras in one. Today you can have up to five multiple streams with a single camera. Even more useful, you can digitally pan, tilt and zoom one view without impacting the other streams.

Utilizing 360º views

360º cameras offer a complete field of view – technically a 180º “usable” view because the camera can’t see behind itself – and are ideal for monitoring small areas. Although these cameras can observe every object of interest all the time, there are some issues if you’re considering replacing multiple cameras with one 360 º view.

First, you dilute the pixel concentration on the sensor over such a wide field of view. As a result, you will end up with less usable data for zooming or post forensics analytics. For example, when utilizing a 5-megapixel 360º camera, you cannot detect a person’s face at 20 feet (This camera’s surface area when set at 20 feet is 2513 sq. ft., giving you only 44 pixels linearly – and you typically need 80 pixels to identify people).

Second, a single overhead-mounted 360º camera can’t offer the same number of perspectives as multiple fixed cameras angled on opposing walls. You may miss crucial activity.

Finally, a single camera will have trouble achieving optimum light balance because large rooms typically have varying lighting conditions throughout. Understand your specific application and environment to ensure a 360º camera is the right solution.

When 5-megapixel is overkill

It’s human nature to want the best. Thus, it’s not uncommon for integrators to request a 5-megapixel camera without reviewing whether it’s needed. A good rule of thumb is to ensure 80 horizontal pixels per foot to identify an individual. With a 6mm lens and a 1/3” sensor chip you can identify a person at the following distances: VGAS (10’), 1.3mp (20’) and 5mp (44’). In other words, for a 20-ft. room, 1.3mp will be perfectly adequate. Furthermore, while a 5mp camera can identify people 120% further away than 1.3mp, 400% more network traffic is needed to send the image.  You will need to weigh the benefits of higher megapixels against this exponential increase in data.

Megapixel IP cameras are game changers. They offer tremendous benefits at only incremental additional costs. But before making the leap, review your needs and environment to maximize your megapixel investment.







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