This article was created out of frustration when I was doing my own research on IP Network Cameras. For anyone new to learning about security cameras, its hard to find much of any spec information online. This post is a collaboration of what I've found after hours of digging.
Minimum Illumination
Minimum illumination is a way to measure the sensitivity of a camera. In another word It's mean, how dark the camera can still see usable image. However because there is no ISO standard to regulate, so each major CCD maker have their own way of testing sensitivity of CCD. However a camera specified as ( 1 lux, F10 ) can be exactly same as the a camera specified as ( 0.01 lux F1.0 )! Why?

More : The most common way to measure minimum illumination is called target illumination. Target illumination means how much light is received by the plan where CCD surface is located. Although the definition is clear however there are three major parameter will dramatically changed the result of the measurement. there are :
Lens f-number (F stop of the lenses used for the camera under test )
Color temperature ( Color temperature of the light source. i.e. spectrum contain )
IRE ( IRE level of the video amplitude )
Reflection ratio ( Reflection ratio of the object and it's background )
Color temperature
Color temperature is the way to express the spectrum contain of the light source. An light source of 3200k contain mostly spectrum around 600nm to 900nm, and a light source of 9300k contain mostly spectrum around 300 to 500 nm. hence different color temperature will totally altered the testing result. A light source with 600 nm wave length will generate 10 times more electron the a light source with 900 nm wave length light source on a typical CCD sensor, hence is 10 time more sensitive. This is why that color temperature must be specified to make the reading meaningful.
IRE level
Maximum amplitude of video output from a CCD camera normally should be set at 100 IRE or 700mV. A video in 100 IRE means that it will fully drive a monitor to expressed best image with best brightness and contrast. a video with 50IRE means it have only half of the contrast. and 30 IRE mean 30% of original amplitude or 210mV. It is generally acceptable that 30 IRE is a minimum value for a meaningful image. A regular camera will have noise level on 10 IRE while AGC kick up to max gain, hence will provide 3:1 or 10dB S/N ratio for a barley acceptable image.
A reading measured under 10 IRE will be 10 times better then measuring read under 100 IRE. so a reading without defining IRE level is actually useless.
Reflection ratio
Reflection ratio of the object and it's background will significantly distort the measurement. An object with 100% reflection rate will generate 100 times more light on target plane then an object with 1% reflection rate.
How do people normally set these parameter :
Most reputable company will measure sensitivity of their camera under following criteria.
F stop F1.4
Color temperature 5600k
Video level 30 IRE
Reflection ratio 80%
So a honest camera make will specify the minimum illumination as
3 lux ( F1.4 5600K 30 IRE 80% )
IF any parameter is omitted the reading can be 10 to 1000 time different .
For example The same camera can be specify very differently
1 lux ( F1.4 5600K 30 IRE 80% )
0.001 lux ( F 0.75 5600K 10 IRE 1% )
This is why some irresponsible make will specify their Ex-view camera actually measured
1 lux ( F1.4 5600K 30 IRE 80% ) but be specified as 0.0001 lux .
Now you know why !!! because they were measured under
( F 0.75 5600K 10 IRE 0.1% )
Curiously want to know if what ( F 0.75 5600K 10 IRE 0.1% ) stands for ?
F 0.75 is the kind of lenses will cost you $30,000 or more to get , and it is not essentially not available for CCTV industry.
10 IRE video is below noise level, so nothing will be seen.
0.1% reflective ratio can be created by putting a tiny white line in front of a very dark background.
Lens f-number
First you need an efficient lens. A lens with a low f-number (such as f1.4) focuses much of the light from your scene onto the camera's sensitive CCD chip. A lens with twice as high an f-number (f2.8) will pass 1/4 as much light through it, making the camera ¼ as sensitive.
Size of the CCD sensor
The camera's CCD chip can be manufactured in a way makes it more sensitive to light. A CCD chip has small squares or elements that are sensitive to light; the more light that falls on these CCD elements, the stronger the signal. The bigger the elements the more light can be collected in a period of time. If we double the size of the elements, we will collect more light. If we increase the size of the elements then the chip size has to be increased. So a ½-inch CCD chip collects more light than a ¼-inch CCD chip. We can also place small micro-lenses on the surface of the chip to concentrate the light and increase the sensitivity of the CCD elements.
SIGNAL-TO-NOISE RATIO (S/N)
The signals from the CCD chip can then be amplified. The more they are amplified, the brighter the picture, but also the noisier the picture. It is like turning up the volume to hear a distant radio station; you hear more music, along with more static and more interference. This electronic noise appears as graininess and color splotchiness in your picture. Improved video circuits amplify the picture signal while adding very little noise. The result is measured using the SIGNAL-TO-NOISE RATIO (S/N) which is measured in dB units. The higher we can make the S/N ratio, the better.
Frame Rate and Shutter Speed
The signal collected on the CCD elements is discharged and transferred to the TV monitor and displayed. The rate that the CCD element is collected is related to the frame rate. Reducing the camera shutter speed also decreases the frame rate. This is another way of increasing camera sensitivity. This allows the light to fall on the CCD elements for a longer period of time. Normally TV cameras make 60 pictures per second. Thus they have 1/60 of a second to collect the light and convert it into a video signal. If the camera made 15 pictures per second, the CCD chip would have 4 times as long to "look" at the picture and absorb the light. It's a little like taking a time exposure with a film camera. Switching to 15 frames per second may quadruple the camera's sensitivity, but it will smear the picture more when objects move (just as it does with a film camera).
THE LENS:
There are a number of different types of lenses. There are fixed focal length, and variable focal length lenses. There are lenses with manual iris and others with auto-irises. Some lenses must be adjusted at the camera, and some new lenses can be adjusted remotely. Here are more details:
Fixed Focal Point Lens: These lenses view a fixed area and you can’t adjust the zoom. They are available with manual and auto iris control. For example the Axis M1101 is a simple indoor camera with a fixed 4.4 mm wide angle lens. It costs under $170
Variable Focal Length Lens: Also called variable lenses, allow you to adjust the field of view by adjusting the focal length setting. These are better lenses since they allow you to make adjustments so that you are viewing exactly what you want. They are available with manual or auto iris.
Iris Control: The iris can be controlled manually or automatically. While it is true that a smaller iris opening often means sharper images, too small an opening may blur an image due to an optical effect called diffraction. This problem can be seen in bright outdoor situations when a camera closes the iris too much and light is diffracted or spread over many pixels. The smaller each pixel is on an image sensor, the more of a problem diffraction becomes because the diffracted light affects more pixels. This can typically happen in cameras that use an automatic DC-iris lens in combination especially with megapixel sensors that have small pixels. (While a megapixel sensor has more pixels than a standard VGA 640x480 image sensor, the size of each pixel on a megapixel sensor is often smaller than the size of each pixel on a VGA image sensor.)
Manual Iris Lens: These lenses are usually used indoors and allow you to adjust the iris opening.
Auto-Iris Lens: The iris of the lens is adjusted by the camera. The iris opening is adjusted automatically when more or less light is required on the sensor of the camera. They are usually required for outdoor cameras. Some IP Cameras like the ones from IQinvision, do not rely on the iris but rather make all the adjustments electronically. The Axis P3343-VE is an example of an outdoor dome camera with an auto-iris lens. This is a very nice camera since the zoom and focus can also be remotely controlled. You can remotely control the view from your computer. It costs less than $1000.
P-iris lenses: P-Iris is a new type of iris control that is both automatic and precise. It works in conjunction with the camera to improve the quality of the video. Unlike a DC-iris lens, the main task of the P-Iris control is not to continuously adjust the flow of light through the lens. The primary objective of P-Iris is to improve image quality by enabling the optimal iris position to be set so that the central and best-performing part of the lens is used most of the time.
The P-Iris works with the electronics of the IP camera. It not only adjusts the iris, it also adjusts the gain (amplification of the signal level) and exposure time. This allows it to manage slight changes in lighting conditions and to further optimize an image. This allows the optimal iris position to be maintained as long as possible. In situations when the preferred iris position and the camera’s electronic processing capabilities cannot adequately correct the exposure, a P-Iris camera will automatically instruct the iris to move to a different position. In dark conditions, for example, the iris will fully open. In bright situations, a camera with P-Iris is programmed to limit the closing of the iris to a position that avoids diffraction or blurring, as explained earlier. Hence, in all lighting conditions, P-Iris can automatically make adjustments to deliver optimal image quality.
Take a look at the two pictures below. You can see the benefits of the p-lens.

Standard auto-iris

P-Iris Lens
At the moment only Axis and CBC have this new functionality. The Axis P1346 and P1347 are examples of cameras with p-iris lenses.
Megapixel Lens: Megapixel cameras require megapixel lenses. These lenses are much clearer than the standard CCTV analog camera lens. They cost more so if you see two megapixel cameras with the same number of pixels but one cost much less, they are probably using a less expensive (not as good) lens.
RESOLUTION
The latest IP cameras have the very nice capability of providing much better resolution than the old analog cameras. You can select cameras with 640 x 480 (VGA) lines to 2592 x 1944 pixels (5 megapixels). The resolution of the camera starts with the sensor, but also includes the lens and quality of the processor and compression used in the camera.
With a higher resolution you can see a wider view. Take a look at the picture below. It gives you some idea of the different views you can see.

To determine what resolution you need, you first consider how wide an area you would like to view and then what detail you need in that field of view. For example, suppose you want to view a doorway and you want to be able to identify a person’s face that comes in the door. In this case you only require a 640 x 480 resolution camera. On the other hand, suppose you want to be able to identify a license plate number in a parking lot that’s 60 ft wide. In this case you need a lot more pixels, and will require a 5 megapixel camera such as the Axis P1347 or IQ755.
COMPRESSION
There are 3 types of compression used by cameras, MJPEG, MPEG4 and H.264. There is some debate about what the best type of compression.
MJPEG requires the most data, provides a complete picture for each frame. Many people say this provides the best resolution.
MPEG4 reduces the amount of data required by only sending the video that change between frames. It improves the compression when there are small parts of the picture that are changing.

H.264 is a version of MPEG4 and provides the best compression. It adds a number of other compression algorithms that dramatically reduce the amount of data transferred. The chart below gives you some idea about the improvement provided by the different compression schemes.

Smart Monitoring A "smart" DVR recording system can be configured to minimize the size of archived video. For example, the system could capture a single JPEG image of an area once every five seconds unless motion is detected. When something moves in the camera's field of view the recording switches back to full frame rate (15 or 30 frames per second).
IP Camera Bandwidth Requirements
| Compression Protocol |
M-JPEG |
MPEG-2 |
MPEG-4 |
| Compression Rate |
6 |
30-40 |
200-500 |
| Resolution |
352 x 288 |
720 x 576 |
720 x 576 |
| FPS |
25-30 fps |
50-60 fps |
25-30 fps |
| Bandwidth Required |
1.5Mbps |
4-15Mbps |
10k-1Mpbs |
Most new cameras from Axis, IQinvision, Sony and others now provide this compression scheme. This compression uses a lot of computer resources so some high resolution cameras can only handle lower frame rates. As an example, the Axis P1347 provides 5 megapixel resolution and up to 12 fps when using H.264 compression. It sells for under $1499.
LOW LIGHT AND AMPLIFICATION:
Camera light sensitivity is measured in lux, which is the amount of light reflected from the object being viewed. The lower the lux number the darker the view. For example, 0.27 lux is the amount of light from a full moon on a clear night, while 500 lux is the light in an office.
The low light performance of a camera is determined by:
· The size and sensitivity of the sensor
· The F-Stop and quality of the lens
· The quality of the video amplifier in the camera
· Day/night capability
Sensor: The larger the sensor the more light hits it, so the higher the light sensitivity.
Day/night cameras can operate in greater range of light levels. When it gets dark the camera automatically removes the IR filter allowing more light to hit the sensor. At night the camera also changes to monochrome mode and improves the total light sensitivity of the system.
Cameras from IQinvision and Axis have good low light performance. For example the Axis P3343 and the IQeye IQ752 can operate in light levels as low as 0.05 lux. This means the cameras can see things even our eyes can’t see.
DYNAMIC RANGE
The dynamic range of a camera is a measure of the minimum and maximum light the camera can see in one frame. Wide dynamic range is helpful when you are looking at a person against a very bright background. Sony has introduced cameras with very wide dynamic range that allows you to see the image on the top.

Sources.
http://www.imakenews.com/kin2/e_article001992240.cfm?x=b8v5FDQ,b25tl0b3,w
http://www.mintron.com/htm/q&a/htm/minimum%20illumination%200.0001%20lux.htm