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Megapixels: What's the Perfect Number?

Posted by Doug Ringer | Feb 9, 2017 4:59:47 PM

When customers ask for the ideal number of megapixels in a security camera, there is no single answer.

With all the camera models that are now available, and with all the variety of applications where those cameras may be applied, it's a matter of matching the application with available imaging solutions on a camera-by-camera basis.

In many cases, customers ask for more megapixels in the hope of getting better image resolution over longer distances. They want to be able to zoom into a point of interest in the distance and have enough pixels to accurately identify people and objects. However, this “more is better” approach to resolution can significantly increase costs for cameras, infrastructure and recording capacity without increasing image quality. In fact, higher megapixel sensors may not perform as well in extreme lighting conditions as high quality 1MP and 2MP cameras. Experienced system designers help define the imaging objectives for each camera location in a system, identify physical and budget limitations, and then apply these factors to determine the megapixel camera resolution and form factor that best meets each camera site’s specific requirements.

It’s all about asking the right questions at the system planning phase. Some typical questions that should be answered before determining which resolution to purchase include:

  • What are you trying to accomplish? Is merely detecting the presence of a person or vehicle sufficient, or do you want to know basic information such as whether an adult or child is present? Do you need to go further and recognize or identify a particular person or license plate?
  • What field of view (FOV) are you trying to cover? Is the camera monitoring a narrow or limited area, or is the camera there for wide-FOV situational awareness?
  • Does a fixed view from this camera meet the need, or does it need to pan/tilt/zoom to change views?
  • At what distance from the camera would like to be able to do these? Are there other possible mounting locations that can be considered?
  • What are the expected operating conditions, including lighting and environmental? Are there options to add additional lighting, for example?
  • What are the bandwidth capacities and limitations of the system infrastructure and how much bandwidth will each camera require at maximum frame rate?

These questions are just a starting point to help pinpoint what’s needed on a camera site-by-site basis. Skilled system designers are aware of these factors, and can help choose the best camera for each location and set of conditions and objectives. While the specifics of each situation will drive the correct answer, the industry does have some general rules of thumb that illustrate the pixel-count challenge.

For example, enhanced low-light performance may be needed to be able to capture acceptable images in low-light environments. Camera with true Wide Dynamic Range (WDR) imaging technology can capture detail from both bright and dark areas in a single scene. When supported by strong low-light and WDR performance, cameras with more megapixels provide the ability to zoom in with greater resolution and detail. Without these extreme lighting (or another modifier for “capabilities”) capabilities, a high pixel count alone will typically not provide the desired image detail, particularly in lower-light and in images with highly contrasted light and dark areas within the same scene.

Another example might be when a designer might say 20 pixels/foot is sufficient for general surveillance applications. That means that after taking into account both the location of the camera, the distance and angles of view, and the resolution of the camera, that 20 pixels will be on the desired target for each 12 inches of target length. At that resolution, users will be able to see basic shapes and colors of cars, people’s clothing and other objects, but will not have enough detail for facial recognition or license plate identification. This is one reason why the objective of system is so important to choosing the correct resolution - 40 pixels/foot is generally the minimum resolution required for facial recognition and license plate identification. To achieve this level requires the camera to have four times the total pixels of the first case, if all other factors are held constant. To read clothing logos or decoration, even higher resolutions would be required. 

As imaging technology continues to quickly advance with higher megapixel resolutions and more powerful processing driving enhanced features and capabilities, security professionals will have more options to achieve their imaging objectives. There simply is no simple answer to the question: “How many megapixels is enough?” By working with an experienced system designer, and by having a clear understanding of the surveillance objectives, physical conditions and budget limitations, security professionals can maximize the probability that their investment in a new or enhanced surveillance system will deliver what they want when they need it most.

Written by Doug Ringer