Choosing the right camera to operate in ambient light conditions may be the most important, but the most deceptive specification, to understand.
Lighting refers to the light falling on a scene. Strictly speaking, the lighting is not a function of the camera. However, it is a critical issue when considering a camera for a given area. Proper lighting is essential to acquire images that allow the personnel security monitor an area (detection), observe activity at the location (recognition), and identify actions specific, objects or persons (identification).
The amount of illumination reaching a scene depends on the time of day and atmospheric conditions. Sunlight directly produces high-contrast scenes, allowing maximum object identification. On a cloudy day, the camera receives less light generating less contrast.
To produce optimal image camera under a wide variation in high (such as when the sun is covered by clouds), you need a system camera with auto iris. Typically, the scene lighting is measured in foot-candles (fc) which vary in a range of 10,000 to 1 (or more).
The table below summarizes the high levels that occur under the lighting conditions during the day and hours of low light. The equivalent metric measure of high level (lux) compared to the condition (fc) is given.
The rule of gold to decide which camera to use for a given lighting condition is not to choose one that delivers a picture just fit for use. Try to give the camera about 10 times the minimum scene illumination. Most cameras will be able to handle the excess light. However, the biggest problem is when they do not have enough light to produce an image.
It should be kept in mind that the camera (such as the human eye) processes the reflected light – on light reflected objects and people that are in the field of view.
The light hits the object and bounces off it. Then, the light passes through the lens, hits the image sensor, and creates an image. Different materials reflect light at different speeds. The table below shows some areas or objects and their corresponding values of reflection – or the percentage of light reflected in them.
The amount of light available, along with the sensitivity of the camera, represent crucial information when choosing a camera for your application. Lighting and sensitivity have an inverse relationship: ie, greater light sensitivity requires less and less light, increased sensitivity is required.
The resolution is the extent to which you can see the details in an image. For analog systems this is typically measured in lines TV (TVL). The higher the resolution, the better the definition and clarity of the image. Camera “scans” an image in a series of lines running horizontally. Each horizontal line is composed of a number of elements. Once the first line is scanned, it continues with the second line and so on. Resolution is a measure of the amount of both the lines and the components that make up each line. In a CCD camera, the resolution has a direct relationship to the number of pixels on the CCD image sensor.
Resolution measures measure the number of horizontal lines a camera uses to produce an image. The horizontal resolution measures the number of elements that make up each horizontal line. The vertical and horizontal resolutions typically yield a ratio of 3: 4 (eg 600 vertical lines for 800 elements per line.). The resolution of the CCTV camera from Deluxesurveillance.com is usually in a range between 380 and 540 TVL.
The higher the camera resolution, more details are visible (because the lines are closer and there may be more elements in each individual line). The low resolution cameras produce images with minor details.
Other important factors
In addition to the primary considerations when selecting a camera, there are other factors affecting image quality. These include:
- Signal to Noise Ratio
- Automatic gain control
- Auto Shutter
- Compensation backlight
- electronic and manual settings
- Advanced Digital Signal Processing (DSP)
Automatic shutter control adds flexibility to the camera by controlling the quality of light. Light sources are composed of different wavelengths of light.
For example, sunlight is almost a pure form of white light – each wavelength is present in equivalent amounts reinforced.
However, other kinds of light (fluorescent, household, lamps, street lights sodium vapor, etc.), the wavelengths are represented matchlessly. These differences can be extreme, resulting in degraded image quality significantly.
While the human eye is able to compensate for many of these differences, one colored camera needs a specialized circuit. Automatic shutters compensate for changes in the quality of light. Thus, an external camera with automatic shutter control can produce accurate images in a parking lot during the day, as under artificial lighting.
Seal is a function of the camera. The basic cameras show or “observe” an image at a rate of 60 times per second (the speed of a shutter 1/60). The technology of digital signal processing in the camera has been improved. Therefore, this circuit can analyze the video signal and if necessary change the frequency of sampling of the image up to 100,000 times per second. This allows darker images can be subjected to more “digital” sampling, using the existing light and thus produce better images.
Backlight Compensation (BLC)
Backlight is the light behind the object of interest in a scene. This may be the biggest problem, especially in the cameras should be adjusted occasionally to maintain the brightness of the background at acceptable levels.
Think about a camera pointing toward a door at the end of a long, dark corridor. When someone opens the door and walks down the corridor, the camera will try to compensate the sudden glow that comes from outside. The result is that the person in the corridor appear as a silhouette and details are lost in the “shadow”. In extreme cases, it may not distinguish any details. The cameras must have a backlight compensation to save the situation.
The backlight compensation is composed of the circuit of the camera and the scene reproducing means in focus objects are objects of interest, and light levels should be optimized for these objects. Light levels extremely high background can be selectively turned off while optimal levels are maintained on objects of interest.
Settings manual and electronic
Like any sophisticated electronic components, cameras require periodic adjustments to maintain high performance. These adjustments must be performed manually in most cases. The newest cameras allow adjustments to be made in the form electronically from remote locations – and the benefits are clear:
- immediate corrections if needed.
- Adjustments are made instantly from a central location.
Consider a camera mounted on a pole in a parking lot. A technician can make adjustments to the camera without worrying about the weather , and without climbing a ladder or use a crane. So, you can save valuable time, reduces the chances of accidents and fewer interruptions in operation.
For example, technology Communication Blinx Bidirectional Bosch uses a conventional CCTV coax, UTP (unshielded twisted pair) and video transmission links via fiber optics to communicate information to and from the camera. The Blix technology embeds control and command configuration in the video signal, enabling many functions that used to require direct access to the camera or to work on a separate video cable wiring.
Advanced digital signal processing
Early attempts to develop video cameras with resolution and sensitivity as good as the human eye – in theory the target principal – were not very successful.
This happened because the eye has a three – dimensional image to the brain , which uses a high degree of parallelism in image processing. The brain ‘s ability to interpret the content of the image at the same time contributes to an intelligent and sophisticated image optimization.
The application of digital technology in the chamber comes from the need to improve image quality, sensitivity and dynamic range. The DSP technology and advanced series of CCD chips produce an exceptionally high number of gray levels, resulting in a dynamic range and detail reproduction in high-quality images in scenes of high and low light.
Clearly, the performance of camera control includes the flexibility of handling it through the monitor screen itself, which is critical when making a choice.
The image quality of a CCD camera is directly related to the number of gray levels that can be processed, which are controlled by the architecture DSP “s. For example, a processor of 1 bit can generate an image similar to the produced by a printer of matrix , while a 4 – bit processor provides 16 levels of gray to produce a better image.
Most security cameras use processors of 10 bits and are capable of producing images with 1024 gray levels, delivering relatively smooth variations from light to dark. Dinion cameras employ a digital signal processing 15 bits, which provides an increase of 32 times the number of gray levels and color accuracy compared to a 10 – bit DSP, producing what the eye interprets as virtually continuous variation gray level. This results in an exceptionally accurate reproduction of images with a wide dynamic range and vivid colors on a broad spectrum.
Wide dynamic range
Roughly defined, the dynamic range of the camera is the difference between the maximum and minimum levels of acceptable signal level. If part of a scene is illuminated poorly, there are high chances that not enough photos from that area to be converted into an electronic signal significant. The detail in the dark will not be “seen” by the camera. Conversely, if a part of the scene is highly illuminated (for example, sunlight entering through a window), the image of that area may appear discolored. In the worst scenario, the scene can and usually does, contain areas with extremely high and low lighting.
The dynamic range is the ability of imaging chip to convert light into information. The wider the dynamic range of the camera, the better the ability of it to meet these extreme contrasts of light. To implement the XF-Dynamic feature, the 15-bit Dinion DSP Bosch uses a feature known as histogram control to get more details on the image to amplify the minute variations in lighting (see example). The lighting of each pixel in a scene obtained by the CCD is recorded in a brightness histogram organized pixels in 32,767 gray levels – in a range from black to maximum brightness in a scene.
The transfer function camera (the curve defining the output as a function of input), rather than being a simple straight line as a normal camera automatically increases strongly in regions with high density of information and less strength in regions with lower density of information.
This creates a brightness histogram more evenly distributed in the chamber outlet.
The low contrast scenes are typically characterized by very high pixel count in just a few levels of gray. In these scenes, the histogram reduces the number of pixels at these levels of gray. At the same time, the pixel count is incremented at other levels (less well represented) to adjust the contrast of the entire image and thus highlight as much detail.
Another aspect of the dynamic range permitted by XF-Dynamic feature of the DinionXF is that it offers an important advantage over the alternative of “dual technology exhibition ” as used in other security systems with cameras. Here, long exposure accumulation time of approximately 1/50 sec. (for PAL) or 1/60 sec. (for NTSC) it is used for the dark areas of a scene, and a short exposure of about 1/1000 second or less is used for the bright areas. A “smart” combination of these two exhibitions is then done – in principle, this should have the best of both worlds, accentuating every detail of the scene without over exposures of bright spots. In practice, the optimal combination is difficult to achieve and compromises, especially, any change between day and night scenes, resulting in less exposure to the optimal and degraded image quality.
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