Megapixels and Math

For the better part of a year, women in certain sections of Brooklyn, NY dreaded the walk home from the subway. A pervert was on the loose, sneaking up from behind, grabbing and groping them. Although he’d been caught on a surveillance camera and the video broadcast on all the local news stations, he remained at large. Viewers could see a youngish man in a black hoodie approaching and attacking but no one came forth to identify him.  The problem was that the quality of the video made it hard to make out the attacker’s face. In a black hoodie and jeans, he could have been any one of thousands, no make that millions of youths.

This was because the camera that captured the incident was a low-cost surveillance camera a  bodega owner had mounted on the entrance to his store, an  inexpensive analog cameras with low resolution and slow frame rate,  probably meant more to deter hold-ups than to give high resolution detail. The culprit was eventually arrested but a megapixel camera would have captured his face in clearer detail and resulted in an earlier arrest. A megapixel camera would also serve the bodega owner better should he ever be robbed.

What is a megapixel? A megapixel is one million pixels. So maybe the question should be what is a pixel?

A pixel is generally thought of as the smallest single component of a digital image, a single point in a graphic image. The word itself is taken from pix meaning pictures and element, short for picture element.         
The way a digital camera creates this copy of a color picture is with a CCD chip behind the lens, constructed with a grid of many tiny light-sensitive cells, or sensors, arranged to divide the total picture area into rows and columns of a huge number of very tiny subareas or light or pixels. The quality of an image, its resolution is dependent how many pixels are displayed and conversely the number of pixels depends on the size of the sensor. If a user wants to see facial features or license plate numbers, megapixel cameras will capture the most detail.

Typical Megapixel Camera Resolutions

Megapixels	Resolution	Total Pixels
1.3	1,280x1,024	1,310,720
2	1,600x1,200	1,920,000
3	2,048x1,536	3,145,728
5	2,592x1,944	5,038,848

To clarify things (no pun intended), let’s take a look at the “lowest” resolution camera in the table. It packs a frame with 1,280 x 1,024 pixels for a total of 1,310,720 pixels or to phrase it differently 1.3 megapixels. The highest non-megapixel camera a D1 using NTSC standards delivers 720x486 pixels per frame for a total of 349,920 pixels, 73 percent less pixels than the 1.3 mega. Not only does the megapixel camera offer finer detail than a non-megapixel but, with the use of the right software and web browser, it can also cover a wider field with the digital zoom feature. Higher resolution and greater coverage seems like a win/win situation. By minimizing the number of cameras he needs, a business owner can lower his costs without compromising his surveillance.
There is something else larger business owners contemplating IP camera networks should consider. The clarity of detail is dependent on the grid size of the camera’s image sensor: the denser the grid, the smaller the pixel ,the smaller the pixel, the higher the total pixel count of the frame. Yes, this results in better resolution but it also requires more bandwidth and increases storage requirements. And that is where compression comes in.
Video compressing is the process of reducing and removing redundant video data so that a video file can be transmitted using the least amount of bandwidth and stored using the least amount of bytes. An algorithm is applied to the source video to compress (encode) it and for viewing, the inverse algorithm is applied to (decode) produce a video that shows virtually the same content as the original source video. A pair of algorithms that work together is called a video codec (encoder/decoder). In   networks where some analog cameras are installed, a video encoder must be installed as well but in most IP networks the encoder is embedded in the IP camera
In order to insure compatibility and scalability (the ability to add more cameras) a codec must fit a standard. Different video compression standards use different methods to reduce data, resulting in different bit rates (transmission speeds), different latencies (the time it takes to compress, send, and decompress) and different quality of the viewed video. Different designers can use different tools to implement compression (encoding) and this is fine as long as the output meets the standard so that it can be decoded.
The different standards used are Motion JPEG, MPEG-4 part 2, and H.264.Within these standards lie different levels or degrees of capability to limit performance, bandwidth and memory requirements. The higher the resolution, the higher the level required. However for now it is sufficient to remember that each standard uses its own  algorithms. Thus  a MPEG-4 encoder will work with a MPEG-4 decoder but it will not work with a H.264 decoder, since it uses a different algorithm, and vice versa.
In our next entry we will explore features such as HD, PTZ capability, low light resolution, and the part software plays. Meanwhile if you are considering a  megapixel or any other type of surveillance camera, contact Kintronics at 800-431-1658 for information and sales. www.kintronics.com.