Is pixel count a good measure of video quality?
For several years now, the video surveillance market has been involved in the “megapixel race,” with manufacturers touting ever-higher pixel counts on their shiny new models. The implication, though not necessarily stated overtly, is that a higher pixel count is equivalent to a better picture. Too simple, says this week’s Expert Panel Roundtable participants, or more to the point: Not true. But where does that leave customers? We asked this week’s Expert Panel Roundtable: Do manufacturers, integrators and/or customers put too much emphasis on pixel count (versus other factors) as a measure of a camera's performance? How can video quality be measured?
Though the pixel race within the industry is prominent, a high pixel count does not guarantee high camera performance and/or higher image quality! A poorly designed camera will still perform poorly regardless of the size of the sensor. I believe that a thorough evaluation of a camera’s performance under different conditions is vital for an objective assessment. There is no “golden rule” that can be applied. Different cameras can produce varying results depending on conditions, and there is no shortcut that bypasses thorough testing.
The recent emphasis on pixel count, or video resolution, is often misleading. The camera may not have a lens that’s good enough to resolve the large number of pixels, for example. Processing high-resolution images is intensive, so most high-resolution cameras give lower frame rates at the highest resolutions – in some applications, such as license plate recognition, this may be unacceptable. High-resolution cameras may have worse low-light capabilities compared to lower resolution cameras. Further, high-resolution cameras sometimes suffer from too much "noise," i.e. graininess, in the image at low light. If the network is not appropriately configured to accommodate the required higher bandwidth of high-resolution cameras, the "quality of service” may suffer; then the video may be "choppy" because of lost frames. Because of the large amount of storage that high-resolution video uses, most users tend to store lower quality video, thus losing the benefit of high-resolution video for investigations.
More pixels provide higher resolution and greater detail, but the overall image quality is one of the most critical yet challenging elements. Every environment produces a variety of (often extreme) lighting conditions and corresponding challenges for a camera. If there are 5 million pixels, but they are all white, it is not helpful. It’s paramount to ensure that critical evidentiary detail is not compromised when a scene contains the concurrent challenges of bright areas, shaded areas, combined with intense lighting conditions. An example is a night-time traffic scene, where it is challenging to see detail in the dark areas next to and between bright headlights. Users need to ensure the chosen camera has the ability to operate accordingly, simultaneously delivering WDR and low-light functionality. Cameras should keep noise to a minimum, preserve image detail and colour information in low-lit scenes, while resolving details in dark and bright areas.
Long experience shows that a CCTV customer who really appreciates all the factors is rare. Others sometimes know that they don’t know. That’s good. They hire us independent technical consultants to help avoid widespread marketplace hype. I find that integrators’ and manufacturers’ staff can range from “proper geek” down to “clueless peddler.” The latter trades on vacuous, numerical headlines claiming “8 megapixels” or “0.01 lux” illustrated with Photoshop-faked comparisons when reality is inconveniently much more complicated. The Laws of Physics don’t vary, so choose among competing realities. More pixels mean smaller pixels, so less sensitive to light. To compensate, cameras amplify and expose pixels for longer, increasing noise and motion blur, both destroying image details. Digital compression can make it worse. Cheap lenses filter out details before they reach your pixels. Poor scene lighting undermines everything. The CCTV industry needs more video engineers than salesmen, but we have the reverse.
Do manufacturers and integrators put too much emphasis on pixel count? Yes they do, way too much, and this does not serve the customer well. In the physical security business, it’s about who has the highest or lowest this or that. This approach is an easy and uncomplicated way to sell and promote a product versus having to be creative solving problems that are unique to each end user. Humans like to take the easy way out. I have more pixels than you so I am better positioned to solve your security problem, so buy from me. This approach is easy and comfortable; however, easy and comfortable is not usually the best way to serve the customer. In most cases, the end user does not care about how many megapixels a camera produces or about other technical minutiae. They have a problem that needs to be addressed and resolved.
Customers should guard against the tendency to equate higher pixel counts with better images. Pixel count is just one of the factors that can impact image quality. In fact, technical specs in general are a risky way of comparing one video camera with another. The only true way to judge is to test them both and decide based on the quality of the video images – isn’t superior video quality usually in the eye of the beholder?
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