MONITORING HD-TVI, IP
Optimization of CCTV camera settings
When selecting a model of a camera we are usually interested in possibility of adjusting to various operating conditions. Of course, more advanced models have more capabilities, simpler devices have some parameters fixed.
However, in order to be able to take full advantage of the adjustments, please refer to their technical data and user manuals. We are here discussing a number of typical settings having an impact on the quality of the image, both positive and negative. Such knowledge will help you achieve the best practical results of the camera operation.
The impact of changes in camera settings will be demonstrated for ACTI cameras, but the rules applye to other types of cameras from different manufacturers.
The main parameter which describes image quality is resolution. It says about how many points the whole image consists of. Of course, the larger the resolution, the better the image quality or larger area that can be monitored. In contrast, it creates a greater demand for bandwidth and increases the volume of recorded material. Typical resolutions: CIF (320 x 240), VGA (640 x 480), D1 (720 x 576), SXGA (1280 x 1024), UXGA (1600 x 1200).
The parameter specifies how many frames are generated/transmitted in a unit of time - the more frames the smoother image. PAL television system has adopted 25 frames per second (fps), which is regarded as completely smooth image. However, due to bandwidth restrictions, video surveillance systems often use in practice frame rates 5 to 10 fps, which are quite sufficient. Of course, there are specific cases that require to use high frame rates, even 100 fps, but such solutions are not popular. Lower frame rates are used to control crowds, higher (25 fps) to monitor the behavior of individuals, the highest to record quick processes (e.g. crash tests).
A very important feature of IP CCTV camera is the kind of video compression. It shows technological level of the camera. The better compression, the lower bandwidth requirements - at the same level of subjective quality. Popular video compression formats are MJPEG (in fact linking consecutive frames compressed as JPEG files) and MPEG-4 (creating complete images one every several frames and refreshing them till the next complete frame only by the changes). The latest and most advanced compression method is H.264 (MPEG-4 Part 10, or MPEG-4 AVC), a block-oriented motion-compensation-based codec standard. It contains a number of new features that allow it to compress video much more effectively than the previous standards, such as multi-picture inter-picture prediction and lossless macro-block coding. In practice, the "gain" of H.264 in comparison with MPEG-4 ASP (bandwidth, file size, or transmission time) is about 30%.
Comparison of popular compression formats at a given quality
Back Light Compensation (BLC).
This function is the ability of a camera to compensate the brightness of the subjects with a large amount of background light that would make it practically impossible to see any details of the subjects. Backlight compensation consists in adjusting the gain of the camera to improve exposure of the subjects that are in front of a bright light source. It allows to identify the foreground. Unfortunately, the background also becomes even brighter.
Wide Dynamic Range (WDR)
This feature of image sensors has been introduced relatively recently. It extends the action of BLC. Due to operation based on the analysis of exposures of single cells, at the same time it can brighten dark elements and darken too bright ones. The image processed this way allows to clearly see details both in the foreground and bright background.
White Balance (WB)
This is a function that influences representation by the camera all the colors, in reference to "white" color. In automatic mode, the reference point for white is the brightest point in the image. Because the camera often monitors an area where the brightest point isn't really "white", the colors in the image can be far from those we consider "real". The solution is to preset colors corresponding to natural or artificial lighting, as well as to save camera settings for a "white" pattern.
Automatic Electronic Shutter (AES)
The possibility of extending the time of opening the shutter allows to increase the exposure of the image sensor. This is a very useful feature in areas with low light, since a longer exposure time results in a brighter image. However, it is not free from drawbacks. The problem is blurring of moving parts of the image. This is due to the fact that the object moves significantly during the period of opening the shutter, being reproduced all the time. Another important limitation is the frame speed of the camera - the opening time cannot exceed the frame time.
JPEG compression has an disadvantage - it generates blocks with undesirable texture. This causes strange patterns in the picture. The effect is particularly visible in dark scenes. The solution to this problem is to reduce the sharpness of the image. Reducing this parameter, one can smooth out the "noise" caused by the compression. Of course, too large reduction would result in a blurred image.
Screenshot of Camera Setup in ACTi cameras
Modern IP cameras offer many options for adjusting to operating conditions. The mechanisms used in the devices allow them to work in almost all conditions. The image quality obtained depends also on the skills of the installer. Please note that the manufacturer presets the parameters to some default conditions that are typical for a specific model. In the actual conditions the installer can improve the picture quality. However, it happens in some cases that the installer worsens the image from the camera to a degree that he may consider it broken. So, if the default settings are satisfactory, there is no need to "experiment". In any case, the changes of the parameters should be made very carefully.
Základné vedomosti (26)
Monitoring miest (8)
NOVINKY V KNIŽNICI
Článok predstavuje koncepty implementácie integrovaných telekomunikačných a RF rozvodov v bytových domoch, ktoré sú v súlade s novými predpismi v Poľsku.... viac »