Making the Most of Megapixel’s Marvels
Welcome to Part I of the latest in SECURITY SALES & INTEGRATION’s acclaimed “D.U.M.I.E.S.” series: “Megapixel Video for D.U.M.I.E.S.” Brought to you by Pelco, this four-part series has been designed to educate readers about megapixel cameras and video — the next phase of surveillance technology following the leap from digital to IP-based, or networked, CCTV systems. “D.U.M.I.E.S.” stands for dealers, users, managers, installers, engineers and salespeople.
Recently, the Megapixel Revolution has begun to affect all of us in the industry. First came the megapixel camera, then megapixel lenses and, of course, megapixel video recorders. Perhaps the megapixel coffee cup is next!
It’s for certain that this changing technology is on a very fast track, and a great deal of hype has surrounded the megapixel revolution. But what exactly is this so-called revolution all about? What is required to support megapixel systems and what are the main advantages of megapixel and IP cameras over analog cameras? The answers lie in this series of articles, which will cover the theoretical and practical technology and design theories required to intelligently sell, install or service megapixel solutions.
Advantages of Megapixel Cameras
Anyone following the megapixel movement has already heard the three main advantages for the incorporation of megapixel technology: 1. better image quality; 2. fewer cameras required; and 3. virtual pan/tilt/zoom (p/t/z). Let’s take a closer look.
Better image quality — The most noticeable advantage of megapixel cameras is image quality. In some cases, this advantage can be confusing or even misunderstood. For example, comparing a standard high-resolution analog output camera producing 580 TVL and a 3.1-megapixel camera can appear to have the same image quality when viewed on a standard monitor (see page A7 for more on image resolutions).
The real test is in the ability to zoom or focus on just a small area of that scene — this is where the megapixel camera will prove to be superior (see diagram right).
Fewer cameras required — When outfitted with high quality wide-angle lenses, megapixel cameras have the ability to cover a much wider area than analog CCTV cameras. It has been stated, “Comparing apples to apples, a 1-megapixel camera can cover more than four times the area of a standard CCTV camera with the same resolution. This means you can replace four CCTV cameras with a single megapixel camera.”
How can one camera replace a total of four standard cameras? The answer is all four would have to be in the same general area (see diagram below). The statement means that when using a very wide-angle lens, a megapixel camera can electronically divide that area into four parts and display each of those sections with the same high quality as if using three or four cameras.
Virtual p/t/z — Another advantage of megapixel cameras is the application of virtual p/t/z, which stems from similar capabilities to the aforementioned multicamera example. Instead of displaying three or four cameras on individual screens, the pixels within the camera sensor are actually addressed in such a way that it appears the camera is moving around a scene.
The main consideration of both the multicamera description and virtual p/t/z is the quality of the lens incorporated into the megapixel system. The characteristics of megapixel lenses will be addressed later in this article.
An additional advantage of megapixel technology is video compression and the reduction related to cable costs and the use of existing cable in system backbones. Bandwidth is a main limitation for megapixel cameras. Due to the structure of the NTSC standard, bandwidth was restricted and, therefore, the need for IP-addressable cameras as well as video compression is an issue.
This will be further detailed in Part II of this series, but, as an example, a 3.1-megapixel camera without compression would require approximately 168MB bandwidth. IT personnel would not exactly be enamored with that type of camera being inserted onto their networks.
In summary, megapixel technology offers many improved features for the surveillance industry such as better image quality, electronic zoom and virtual p/t/z systems. Are these sufficient enough to offset the high price of equipment? It depends on the particular application, how shrewdly these advantages are deployed, and how the return on investment (ROI) and total cost of ownership (TCO) results are calculated. Sometimes, more money spent now can mean savings down the line for the end user.
It’s for sure that megapixel technology has a place in the security industry, but only time will tell the full measure of its ultimate impact.
CMOS Image Sensors Come of Age
What changes to camera technology have led to the megapixel revolution? The first and foremost advancement is the camera sensor. Through the years the sensor has gone through many stages of increased performance. The early sensors incorporated in surveillance cameras consisted of either CCD or CMOS chips.
CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) image sensors are two different technologies for capturing images digitally. Each has unique strengths and weaknesses that lend advantages in different applications. For a long time, CCD has been the most popular choice for video surveillance use. But during the past five years much has changed with both technologies, and the current situation seems to favor the CMOS sensor.
Both types of imagers convert light into electric charge and process it into electronic signals. In a CCD sensor, every pixel’s charge is transferred through a very limited number of output nodes to be converted to voltage, buffered and sent off-chip as an analog signal. All of the pixel can be devoted to light capture, and the output’s uniformity (a key factor in image quality) is high.
In a CMOS sensor, each pixel has its own charge-to-voltage conversion, and the sensor often also includes amplifiers, noise-correction and digitization circuits, so that the chip outputs digital bits. These other functions increase the design complexity and reduce the area available for light capture. With each pixel doing its own conversion, uniformity is lower. But the chip can be built to require less off-chip circuitry for basic operation.
The main reason for the success of the CCD over the CMOS in the early stages of video surveillance was the lower noise, less video smearing and blooming found in CMOS devices. However, with the increased performance of CMOS devices and the fact that it is truly a digital output and requires less power to operate, CMOS chips have become the choice for IP and megapixels cameras.
The main advantages of today
’s CMOS devices include:
• Much lower power
• System-on-a-chip integration allows smaller cameras
• Lower cost of sensor chip and fewer components in camera
• Easy digital interface for faster camera design
• Less image artifacts — no blooming or smear, with same sensitivity
• Higher dynamic range for security applications
• Digital output for faster readout speeds and frame rates
• Direct addressing of pixels allows electronic p/t/z
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