Welcome to the Dark Side
Technology has conquered many of the obstacles to good low-light surveillance.
Seeing in the dark isn’t just a science, it’s an art. For the 31 years I have been in the security industry, the goal has been to see in the dark. We have combated the empty voids with white light, infrared light, excited electrons in third- and fourth-level intensifiers. We have tweaked and tuned our technology until it feels as though there is nothing else that can be done. And then, right when you think it’s over, someone comes along and gives it another shot in the arm. So we continue to attack and defeat our dark side.
But there are plenty of obstacles to contend with. We have lens light-loss factors. We have distance issues. We have image clarity problems. We have color issues. We have inconsistent light reflectance issues. We have crap in the air to deal with. We have the technical process of deciding between intensification or just building a better mousetrap. And last, we have the dark itself ... the void ... the absence of light or reflective light. The absence of the very thing our eyes and cameras require to create an electrical pulse that is deciphered into an image.
We measure this light loss in f-stops. One f-stop gain is equal to a 50% reduction in the light passing through the lens. One f-stop loss is equal to a 100% increase in the light. All lenses have light loss. If they didn’t, their rating would be f-0.
A camera’s sensitivity is based upon the lens that it was tested with—usually an f-1.4. So the first step to low-light vision is to improve the quality of the lens. Not necessarily an easy or inexpensive thing to do. However, with our improved technology, most low-light images could be greatly improved if the designer would only install a better-quality lens. The lenses are out there and very available.
The bottom line is a catch-22. If you want to increase your light intake to the camera, you use a wider-angle lens. However, if you want to identify your subject, you need to use a telephoto or zoom lens. By going telephoto, you narrow your light-gathering area dramatically and you increase your lens light-loss factor.
Auto gain circuits were originally designed to keep the image consistent as the image travels through shadows. The unfortunate side effect of this circuit is that in the process of amplifying the video image, it also amplifies the noise level, creating a very grainy image and throwing clarity out the door. So in most low-light camera technology, the AGC must be greatly filtered or dropped completely.
Intensified cameras use an electron exciter mounted in front of the CCD. As light enters the exciter, the electron flow of the light is intensified, thus giving the illusion of amplified light. The natural side effect of this process is an equal distribution of white noise in your image as the light levels drop. Thanks to digital technology, a great portion of this noise is now able to be filtered out of our images.
Thanks to digital technology, video now has the ability to restore colors to their original intensity. This has opened the door for a whole slug of good, low–light, color cameras. Whereas in the past we were restricted to light levels of 1 fc or more for color images, today we are able to reach into the depths of .01 fc and less.
Inconsistent Scene Illumination
Weather and Dust
We have attacked fog, snow, rain and high dust with yellow, red and infrared lighting techniques. This works because the longer wavelength of light can move through and between the various molecules of interference, avoiding a great percentage of reflectance. However, it does not solve low-light viewing problems.
For this, technology again steps in. Using a combination of extreme resolution and digital filtering, we have cameras that not only see through these various debris, but do it at distances of up to 10 km. Just the kind of stuff that is needed and being used on borders and ports and in jungles.
So, all said and done, where are we with low-light cameras? We are in great shape and getting better all the time. Color cameras are available in a wide range of sensitivities going all the way down to .01 fc and further. It all depends upon your application and budget. Black-and-white technology drives down the sensitivity to .000005 fc. Then, of course, we have specialty technology for viewing extreme distances at extreme low levels of light that I just can’t add enough zeros to. The bottom line: Your applications in the dark are easier to see than ever before. What used to cost us tens of thousands of dollars, we are now producing for less than half or even one quarter of the cost. Open your eyes and you will see.
By Charlie R. Pierce
LeapFrog Training & Consulting