If you think resolution and image quality are essentially the same, you’re not alone. But the truth is: pushing the megapixel limit ever higher doesn’t necessarily give you a better picture. So if resolution isn’t the primary measure for image quality, what is? To answer that, you really need to understand what it is you’re trying to achieve. As a security professional your goal isn’t so much image quality as it is image usability: how well the image delivers the situational awareness you need from a given scene. Usually this is defined as being able to detect, recognize, and/or identify a person or object within the field of view.
In shifting the discussion from image quality to image usability, it quickly becomes apparent that resolution is only one of a number of factors to consider when selecting a 4K or other camera for an installation. While adding more pixels certainly impacts resolution, in many cases it also degrades other factors that drive image usability such as color fidelity, frame rate and aspect ratio.
Establishing a standard for image usability
Ultra High Definition (UHDTV) – more commonly referred to as 4K – controls the interplay among these factors by defining specific parameters:
- Resolution – With a resolution of eight megapixels security professionals can achieve more pixels on target with wider fields of views.
- Color fidelity – The broader palette provides more accurate color rendition which is important for security when verifying the color of a car or the clothing someone is wearing.
- Frame rate – Delivering 30 frames per second (FPS) increases situational awareness especially in the midst of highly volatile and fluid events.
- Aspect ratio – Producing images in the 16:9 aspect ratio affords broader coverage of the scene and presents unique advantages when surveilling long corridors or narrow spaces over distance.
It’s all in the details
So what does this mean in terms of image usability?
More pixels on target. It is generally accepted that 80 pixels across the width of a person’s face provides sufficient detail for a positive identification. Because 4K cameras deliver the equivalent of eight megapixels or eight million pixels, they enable security professionals to deploy fewer cameras across a broader area while still maintaining the pixel density needed for the operational requirement.
For example, retail establishments typically use surveillance cameras to protect their properties, including the parking lot. Most of these businesses mount the camera on the building with a field of view directed towards the parked cars. Deploying higher resolution cameras equipped with wide-angle lenses not only delivers greater coverage with fewer cameras but also increases the depth of field which provides larger areas of focus. The additional pixels make it possible to extract great detail when digitally zooming in on an area of interest during live view or post incident review.
Precise color. Have you ever seen video on a display that just didn’t look the same way as the scene did with the naked eye? Color rendition isn’t always easy for cameras to reproduce accurately. With security, the color of a car or clothing has real forensic significance. So if a central station operator contacts law enforcement regarding a suspicious person wearing an orange jacket loitering near an ATM and it is really red, the wrong person might get some unwarranted attention.
With a broader palette to work from, 4K produces images that accurately represent the reality of people, objects and backgrounds in a scene. Paired with corresponding 4K television displays, the color rendition provides accurate representation in both real-time and post incident forensic review. Speaking of displays, if the resolution does not exceed or meet the resolution of the camera then what have you really gained? Most cable networks broadcast both HD and standard definition versions of the same programming. Try switching back and forth the next time you are watching your favorite sport and look at the crowd versus the athletes. Are you missing some details? Of course you are. And the same is happening when you view higher resolution surveillance images on displays that don’t match the cameras’ resolution.
Fast scene capture. A big factor contributing to situational awareness is the number of frames per second (fps) that a camera is able to deliver. The eye perceives full motion video at around 16 fps, but most security cameras can deliver 30 fps. In fact, the HDTV standard defines a minimum frame rate of 30 fps. With a higher frame rate the camera can capture quick movements like a card shark’s slight-of-hand or the denomination of the bill the cashier sneaks from the till.
Flexible aspect ratio. The display you are reading this article on most likely has an aspect ratio of 16:9 which is the dominant form factor for displays over the last decade. Almost all broadcast, consumer and online content conforms to this defacto standard and like most consumer electronic trends, the security industry has followed suit.
4K displays are the new rage in the consumer electronics and broadcast industries despite their high cost and limited content available for viewing. The security industry, on the other hand, will probably be in the top ten of 4K content generation in 2015 though nobody other than security professionals will see it.
The large screen aspect ratio has another important application: flipping the image orientation from a horizontal to vertical (a 9:16 aspect ratio). Think of hallways, warehouses with high shelves or even city streets lined with high-rise buildings. By changing the aspect ratio to 9:16, we can deliver more pixels in the area of the image where an event will occur. What’s more valuable – lots of pixels on the empty walls of a hallway or more pixels on the person walking down it?
Why 4K isn’t for everyone
Even with all these factors going for them, it’s unlikely that 4K cameras will become the dominant camera offering on the market any time soon. That’s because there are currently a number of significant limitations that are impeding adoption:
- Light sensitivity decreases as the pixels get smaller on higher resolution cameras. This directly impacts the environmental options in which 4K cameras can be placed. Confined to the same real-estate on the sensors, these smaller pixels require higher light levels to activate and therefore aren’t as effective in lower light situations. The same issue applies to the dynamic range of the camera, which measures the cameras ability to capture both the light and dark areas of a scene.
- Bandwidth and storage are major factors for users with constrained budgets. 4K consumes four times the bandwidth and storage of the most popular 1080p HDTV cameras, making it four times as costly to deploy.
- Lens technology isn’t keeping up with image sensor advances. As a result, there are few lens options for 4K cameras. Since 4K cameras cannot use the standard CS-mount lens commonly used in the security field this leaves the end user stuck with the lens the manufacturer ships with the product.
- Opportunities that justify the benefits of 4K are few and far between in the majority of today’s camera installations. In many instances a 4K camera would be overkill for the operational requirements. Higher resolution cameras are most applicable in large, open areas that have controlled lighting conditions. Think warehouses, parking lots, stadiums, foyers of an office building, all of which would require a higher density of lower resolution cameras to adequately cover the space. In most cases this is a lower number of cameras than traditional HDTV solutions.
The 4K sweet spot
In the end, 4K cameras offer real value for security practitioners who need to monitor and record large areas. Their higher resolution enables the use of wider field of views while maintaining the appropriate pixels on target to meet operational requirements. With 4K you get the added benefit of a standard that defines expectations up front and delivers greater image usability from surveillance recordings.
About the Author: James Marcella has been a technologist in the security and IT industries for nearly two decades. He is currently the director of technical services for Axis Communications.
