Super Sizing with Megapixel Cameras
The improved clarity provided by megapixel cameras was first applied to broadcast applications when television stations started migrating from NTSC to HD (high definition). Poorly constructed sets and props such as fake bookcases with painted-in books didn’t cut it when shot with high-resolution HD cameras. In the video surveillance arena, the clarity and precision of images from megapixel cameras can provide indisputable details that were previously unavailable with conventional CCD cameras. Needless to say, this is of particular importance for live surveillance as well as with recorded footage in forensics applications.
Another advantage of using megapixel cameras for surveillance applications is that a single megapixel camera with a wide-angle lens can often replace several conventional cameras and, depending on your application, possibly result in a lower overall system cost and increased image quality. For instance, positioned in the corner of a room, a 3.0 megapixel security camera using a 90o lens can provide a clear range of vision over the entire room, thus eliminating the need to employ cross-coverage cameras. The camera can be powered over the Ethernet (PoE), thereby reducing cabling costs as well as a reduced cost for multiple brackets, housings, lenses, etc. Any part of the raw image can be zoomed in upon, providing in most cases, the same or better quality image then if you had multiple high-resolution CCD cameras placed over the same subject.
The Megapixel Ratings RaceOne would naturally think the more pixels, the better the quality of the image, but this is not always the case. While some have mastered this process and produced results better than others, the fact remains that CCDs are becoming progressively smaller. Trying to fit an increased number of pixels on shrinking real estate can result in the pixel size becoming smaller than the resolving power of the optics.
The consequence is a poor quality image containing blurring or chromatic aberrations.
However, megapixel cameras designed for the security market tend not to suffer as seriously in the megapixel ratings race. Many of these newer cameras that have hit the market utilize ½-inch optical formats on CMOS image sensors instead of CCD technology. While cameras are available with 10 or more megapixel ratings, these are intended for use in critical security or specialized applications such as military applications. Generally, a three or five megapixel camera is ideal for mainstream video surveillance applications on a network, which is limited by the amount of traffic it can carry.
Compression and Data ManagementBecause megapixel cameras resolve so much detail, bandwidth usage and video storage can quickly become an issue. Both are dependant on the compression format used in the camera (Motion JPEG or MPEG-4 are two of the most common) and the frame rate at which the video is transmitted. Without going into too much detail, Motion JPEG is full frames of video, compressed in sequence to give the impression of motion. Each image or file is quite large and can consume an excessive amounts of bandwidth when sent at a full 30 fps (frames per second), but the compression technology is simple and fast and there is virtually no lag or latency which can affect PTZ control, video motion detection or object tracking. When frame rates are adjusted to limit bandwidth usage, image quality is not lost.
MPEG 2 and 4 compressions are more complex and work by compressing only the changes from one frame to the next in a limited sequence before the process is refreshed and the next full frame is compressed. This method has the advantage of lower volume data to help ease bandwidth usage while maintaining a relatively high level of quality. The compression complexity results in a higher latency or time lag when compared to Motion JPEG. However, because disk storage is directly related to bandwidth, MPEG is usually better suited to restricted space storage devices.
Implementing megapixel cameras into existing and new systems needs to be handled with the utmost attention. Bandwidth and storage need to be calculated up front before a system can be designed and quoted. Look at it this way; a lot of people have digital cameras and e-mail pictures to their friends with image files typically as large as 2MB. Translate that into a security application and imagine sending and recording thirty 2MB images a second over your network every second, 24/7. Even with a few megapixel cameras in place, there is a dramatic increase in bandwidth and storage capacities. So, it’s important to weigh the bandwidth and recording requirements needed to accommodate megapixel cameras in the system – then weigh the costs associated with these additions relative to deploying conventional cameras. If video requirements call for the added detail and definition megapixel cameras offer, you may find the associated costs warranted.