Ask Before Buying

Not all products are created equal, so it is important to ask the right questions

• By Allen Chan
• Sep 01, 2015

There is little arguing that 4K is positioned to become the next imaging standard in the security industry. Nearly every major camera manufacturer today, including Sony, has a 4K offering, and large VMS providers offer support for 4K cameras. In addition, early adopters of 4K surveillance cameras include cities, transit operators and campuses. According to the latest market data from IHS Inc. for the Americas, revenue from the sale of network cameras with four or more megapixels is forecast to grow more than twice as fast as the average for the network camera category in the next four years. “4K will be a major driving force for the high megapixel network camera market,” said Josh Woodhouse, senior analyst for IHS. “In a similar manner to HDTV, end-users are expecting the same high-quality 4K compliant video from their surveillance systems as they are seeing emerge on their consumer devices.”

Early end users are drawn to the resolution of 4K, which is four times that of full HD, as well as 4K’s ability to increase wide area surveillance while still capturing, magnifying and examining the smallest parts of a scene. Looking at a section of a larger 4K image, the increased number of pixels captured means that objects are more defined compared to a high-definition image. This makes it easier to identify smaller details, as the content is less blurred. Higher 4K resolution also means more accuracy. Most security applications usually require either situational awareness or detailed monitoring of specific areas of an image, especially for postincident analysis. With 4K, it is possible to achieve both situational awareness and detailed monitoring at the same time.

Unfortunately, there is no standardization around how camera specifications are written, which has been problematic in the security industry. To this day, 4K cameras are no exception. Camera specification sheets appear to offer comparable features across the board, but they do not tell buyers the true capabilities of a product. For this reason, it is not enough for security professionals to simply compare datasheets and make purchasing decisions based solely on specifications.

Purchasers need to ask manufacturers several detailed questions before deciding which 4K cameras are actually going to meet all of their installation requirements.

Is the Lens Optimized for 4K?

Resolution, as defined by the image sensor, does not necessarily translate to the other optics that may be included with a camera. For example, the lens also needs to be well-matched to the image sensor. Even with the best 4K image sensor in place, the wrong lens can limit the camera’s overall performance and inhibit the production of 4K quality pictures.

In order to capture full 4K resolution, a camera’s lens needs to be at least eight megapixels. However, lenses with such high resolution are expensive; particularly those that can support the zoom movement required for so many security and surveillance applications.

To make their cameras more affordable, some manufacturers use lenses that are not built for 4K imaging. Doing so does reduce costs, but it can also degrade resolution to the point that the camera should no longer be classified as truly 4K. While the overall picture may appear “good enough,” users will certainly start to notice the difference when zooming in on the finer details of a scene.

The physics behind this are quite complicated, but they boil down to a few important points. Image sensor design has evolved around the idea of smaller and smaller pixel sizes. The smaller the pixel size, the more of them that can fit on the senor. However, this leads to a mismatch between the sensor resolution and the lens. A 4K camera lens needs to employ higher optical performance and lower F-numbers so that it can take advantage of all the information generated by the 4K image sensor.

In addition to resolution, the overall quality of a lens is impacted by other important specifications like the Mean Transfer Function (MTF), the F-stop normally associated with the “speed” of the lens, and other parameters.

Why is Minimum Illumination Important?

Today, most 4K cameras have poorer minimum illumination ratings than their full HD counterparts, meaning that they require more light to produce usable images and will switch from color mode to black-andwhite mode before an HD camera. This is simply because when using similar sized imagers, the sensor area to gather light becomes smaller as resolution increases.

As there is no standard for minimum illumination in the security industry, it is important that the specifications from different products be “normalized” to a set parameter. As an example, Sony uses 50 percent video level, with a defined set of conditions like a normal shutter speed of 1/30 second, AGC ON, with a lens F stop of 1.6. When the shutter speed is slowed down by 50 percent, it results in a minimum illumination number which is approximately two times better.

Of course, sensor sensitivity improvements are a factor as well. Most 4K cameras still bring in light using a front-illuminated structure. However, a backilluminated structure can more than double the camera’s light sensitivity characteristics. A back-illuminated CMOS sensor will have more than two times better sensitivity than a conventional CMOS sensor. In order to compensate and increase gain, many 4K cameras simply use a slower shutter speed that allows more light to be “stored” to the image sensor. However, this may not be ideal as any moving objects will easily become blurry or grainy with gain being too high.

In situations where lighting is really poor, (IR) illuminators can be deployed. The challenge when using external IR sources is how to maintain overall picture clarity as objects move from far to near or vice versa. Having a built-in IR light source allows the camera to better control the illumination level or exposure.

How Does the Camera Manage Bandwidth Consumption Concerns?

When resolution goes up, bandwidth consumption and storage needs also increase. This can make deploying 4K cameras more expensive and more challenging than deploying full HD cameras.

Most 4K surveillance cameras today use the H.264 video coding format. This is a standard coding format used in many kinds of video, including Blu-ray discs, HDTV broadcasts and online streaming for sites like YouTube. However, because 4K video contains so much more data than full HD, using a standard method of compression is not enough to keep bandwidth consumption in check.

Using region of interest (ROI) coding is one way to mitigate bandwidth and storage challenges, using less compression and therefore better image quality only in the important areas of the picture and only when needed. Most of the time, only particular areas of the video are of interest—such as a moving car or a store entrance. ROI allows users to view enhanced details of the relevant area while transmitting and archiving extraneous parts of the image in a lower resolution.

Some 4K cameras can be programmed in advance for static (still) ROI. Another way is to use dynamic (moving) ROI, using analytics like motion detection to determine the critical region, or a combination of both static and dynamic. Analytics in the camera can also be used to dynamically crop the area of interest and stream only this region back to the head end.

For example, Sony’s use of ROI—Intelligent Cropping—allows users to select the portions of an image that they want to see in its native resolution. All other parts of the image are transmitted at full HD resolution, resulting in lower bandwidth consumption by reducing the amount of video transmitted. In other words, you are not transmitting in 4K if images are cropped.

Although widespread adoption is still several years away, 4K is already emerging as the next imaging standard for security and surveillance applications. Security professionals need to be armed with the right information and the right questions to ask vendors so that they can make the right choice for their 4K needs today and well into the future.

This article originally appeared in the September 2015 issue of Security Today.