| Introduction | | | | |
| When selecting a model of a camera we are usually | | | | Comparison of popular compression formats at a |
| interested in possibility of adjustments to various | | | | given quality |
| operating conditions. Of course, more advanced | | | | Back Light Compensation (BLC) |
| models have more capabilities, simpler devices keep | | | | This function is the ability of a camera to compensate |
| some parameters fixed. | | | | the brightness of the subjects with a large amount of |
| However, in order to be able to take full advantage of | | | | background light that would make it practically |
| the adjustments, please refer to their technical data | | | | impossible to see any details of the subjects. Backlight |
| and user manuals. We here are discussing a number | | | | compensation consists in adjusting the gain of the |
| of typical settings having an impact on the quality of | | | | camera to improve exposure of the subjects that are |
| the image, both positive and negative. Such knowledge | | | | in front of a bright light source. It allows to identify the |
| will help you achieve the best practical results of the | | | | foreground. Unfortunately, the background also |
| camera operation. The impact of changes in camera | | | | becomes even brighter. |
| settings will be demonstrated for ACTI cameras, but | | | | |
| the rules apply to other types of cameras from | | | | Wide Dynamic Range (WDR) |
| different manufacturers. | | | | This feature of image sensors has been introduced |
| Resolution | | | | relatively recently. It extends the action of BLC. Due to |
| The main parameter which describes image quality is | | | | operation based on the analysis of exposures of single |
| its resolution. It says about how many points the whole | | | | cells, at the same time it can brighten dark elements |
| image consists of. Of course, the larger the resolution, | | | | and darken too bright ones. The image processed this |
| the better the image quality or larger area that can be | | | | way allows to clearly see details both in the |
| monitored. In contrast, it creates a greater demand for | | | | foreground and bright background. |
| bandwidth and increases the volume of recorded | | | | White Balance (WB) |
| material. Typical resolutions: CIF (320 x 240), VGA | | | | This is a function that influences representation by the |
| (640 x 480), D1 (720 x 576), SXGA (1280 x 1024), | | | | camera all the colors, in reference to "white" color. In |
| UXGA (1600 x 1200). | | | | automatic mode, the reference point for white is the |
| | | | brightest point in the image. Because the camera often |
| Frame rate | | | | monitors an area where the brightest point isn't really |
| The parameter specifies how many frames are | | | | "white", the colors in the image can be far from those |
| generated/transmitted in a unit of time - the more | | | | we consider "real". The solution is to preset colors |
| frames the smoother image. PAL television system | | | | corresponding to natural or artificial lighting, as well as |
| has adopted 25 frames per second (fps), which is | | | | to save camera settings for a "white" pattern. |
| regarded as completely smooth image. However, due | | | | |
| to bandwidth restrictions, video surveillance systems | | | | Automatic Gain Control (AGC) |
| often use in practice frame rates 5 to 10 fps, which | | | | This allows an increase in sensitivity, enabling operation |
| are quite sufficient. Of course, there are specific cases | | | | in lower light conditions. However, it should be borne in |
| that require to use high frame rates, even 100 fps, but | | | | mind that with the strengthening of the signal, the noise |
| such solutions are not popular. Lower frame rates are | | | | is amplified as well. So the AGC level has to be set |
| used to control crowds, higher (25 fps) to monitor the | | | | carefully, on a trial-and-error basis. |
| behavior of individuals, the highest to record quick | | | | Automatic Electronic Shutter (AES) |
| processes (e.g. crash tests). | | | | The possibility of extending the time of opening the |
| Compression | | | | shutter allows to increase the exposure of the image |
| A very important feature of IP CCTV camera is the | | | | sensor. This is a very useful feature in areas with low |
| kind of video compression. It shows technological level | | | | light, since a longer exposure time results in a brighter |
| of the camera. The better compression, the lower | | | | image. However, it is not free from drawbacks. The |
| bandwidth requirements - at the same level of | | | | problem is blurring of moving parts of the image. This is |
| subjective quality. Popular video compression formats | | | | due to the fact that the objects move significantly |
| are MJPEG (in fact linking consecutive frames | | | | during the period of opening the shutter, being |
| compressed as JPEG files) and MPEG-4 (creating | | | | reproduced all the time. Another important limitation is |
| complete images one every several frames and | | | | the frame speed of the camera - the opening time |
| refreshing them till the next complete frame only by | | | | cannot exceed the frame time. |
| the changes). The latest and most advanced | | | | Sharpness |
| compression method is H.264 (MPEG-4 Part 10, or | | | | JPEG compression has a disadvantage - it generates |
| MPEG-4 AVC), a block-oriented | | | | blocks with undesirable texture. This causes strange |
| motion-compensation-based codec standard. It | | | | patterns in the picture. The effect is particularly visible |
| contains a number of new features that allow it to | | | | in dark scenes. The solution to this problem is to |
| compress video much more effectively than the | | | | reduce the sharpness of the image. Reducing this |
| previous standards, such as multi-picture inter-picture | | | | parameter, you can smooth out the "noise" caused by |
| prediction and lossless macro-block coding. In practice, | | | | the compression. Of course, too big reduction would |
| the "gain" of H.264 in comparison with MPEG-4 ASP | | | | result in a blurred image. |
| (bandwidth, file size, or transmission time) is about 30%. | | | | |