One of the most difficult challenges when designing a new security video surveillance system is the decision making process that goes into choosing the cameras. Anyone who has developed a camera system before is familiar with the myriad trade offs that make up the solution. High camera resolution leads to higher quality images, but larger storage and bandwidth needs. This can be offset by compression and frame rate adjustments, but leads to a lower image quality over all. Don’t forget about field of view and lens focal length. Now tie in light sensitivity and sources of illumination. All this makes for one pretty complicated set of variables.
Now add to the mix the common idea that ‘more is better.’ Some camera manufacturers will have you believe that more is always better, that you must have the newest technology with the largest megapixel camera available. Frankly this isn’t always true. Oh sure, technology has advanced to the point where you can do some absolutely amazing things with high megapixel cameras. And under the right circumstances, high megapixel cameras can save you plenty of money. But the key to finding the most value in your security solution is not to use the “best” technology, but to use the right technology.
A Word About Resolution
The term resolution refers to the number of the smallest picture elements or pixels that make up a video image. The more picture elements, the better the detail of the picture. Resolution for analog cameras is typically measured in Television Lines or TVL where resolution in digital cameras is typically measured in pixels and communicated by either the number of pixels both horizontally and vertical (such as 640 x 480) or as a total number of pixels in the image (such as 1.4 megapixels).
The term resolution refers to the number of the smallest picture elements or pixels that make up a video image. The more picture elements, the better the detail of the picture. Resolution for analog cameras is typically measured in Television Lines or TVL where resolution in digital cameras is typically measured in pixels and communicated by either the number of pixels both horizontally and vertical (such as 640 x 480) or as a total number of pixels in the image (such as 1.4 megapixels).
In a camera system, resolution is typically the balancing factor. Depending on the purpose of your system, you may need a large resolution in order to recognize faces or licenses plates. Under other circumstances, you don’t need a high resolution at all because your field of view is so large you only want a general idea of what is happening. Typically adjustments to a camera system are made to get the most resolution with the lowest storage and bandwidth requirements.
Pixels Per Foot (PPF)
To determine the needs of the surveillance solution and what types and numbers of cameras are necessary, system designers will often use the measurement “pixels per foot” or PPF. This measurement is similar to camera resolution, but refers to the resolution of the final video produced based on the size the area the video is recording. For instance, a rule of thumb is that the minimum resolution required for facial recognition is 40 PPF. So if you are using a camera to monitor an entrance that is 20 feet wide and you wish to provide facial recognition, you’re going to need a camera with a resolution at least 800 pixels wide.
To determine the needs of the surveillance solution and what types and numbers of cameras are necessary, system designers will often use the measurement “pixels per foot” or PPF. This measurement is similar to camera resolution, but refers to the resolution of the final video produced based on the size the area the video is recording. For instance, a rule of thumb is that the minimum resolution required for facial recognition is 40 PPF. So if you are using a camera to monitor an entrance that is 20 feet wide and you wish to provide facial recognition, you’re going to need a camera with a resolution at least 800 pixels wide.
Of course, distance from the area to be viewed matters when it comes to the final video resolution. The farther away the camera is from the subject, the larger the camera resolution needs to be to obtain a final video resolution of 40 PPF. This is where field of view and lenses come into play. If you moved your camera to cover the 20 foot opening and 10 feet of wall on either side, your total area of coverage has increased to 40 feet, meaning that you’ll need a camera resolution of at least 1600 pixels wide in order to keep the same 40 PPF video resolution. However, using a different lens or optical zoom to focus the camera’s field of view on the 20 foot area you want to view will allow you keep the same resolution requirement of 800 pixels.
More Cameras or More Megapixels?
So what if you need to record that entire 40 foot area? If you used a single 800 x 600 resolution camera to do so, you’d have a final video resolution of 20 PPF. Not good enough to reliably recognize a face. So your options are to either use a single 1.9 megapixel camera, or divide the viewing area between two smaller cameras focused in on a 20 foot area each. At first glance, the two standard IP cameras may seem the least expensive option because of the lower price of standard digital cameras over megapixel cameras, but depending on your system setup, it may be that using a single megapixel camera to replace multiple IP cameras is the most economical option.
So what if you need to record that entire 40 foot area? If you used a single 800 x 600 resolution camera to do so, you’d have a final video resolution of 20 PPF. Not good enough to reliably recognize a face. So your options are to either use a single 1.9 megapixel camera, or divide the viewing area between two smaller cameras focused in on a 20 foot area each. At first glance, the two standard IP cameras may seem the least expensive option because of the lower price of standard digital cameras over megapixel cameras, but depending on your system setup, it may be that using a single megapixel camera to replace multiple IP cameras is the most economical option.
This of course just scratches the surface of the calculations and tradeoffs that go into designing a video surveillance system. There are plenty more variables to consider. But the old adage “waste not, want not” can be very applicable when choosing which cameras to implement. Choosing the right camera for your needs will ensure your video surveillance system will function how you need it without demanding too many resources. Choosing a camera with a much larger resolution than you really need will only eat up additional resources without providing additional value.
In every solution there is a tipping point where you’ll find the most value for the lowest investment. Have you found that tipping point in your own solution? Leave your comments and let us know how you feel about your own camera choices. Did you choose a larger resolution than you really need? Or are you struggling with a system that fit your budget, but isn’t providing the quality you really want?
No comments:
Post a Comment