Camcorder Slr
What is the best video camera for surveillance?
Author: Josh White
To View all the figures / graphics / illustrations referenced in this article, click here.
S ummary
Looking for a digital camera for use in the monitoring exercise? However, technological improvements in CCD image sensors and CMOS sensors and the introduction of new screen high definition recording formats have undoubtedly led to the introduction of different models of digital camcorders. Due to the wide variety of features and price, it is more difficult than ever to choose the best digital video camera. Certainly, some models are better than others in examining the specific application for which the camera is designed and features that are necessary. Because there are so many factors involved in the selection and from the new models are introduced often, it is best to provide useful guidance for model evaluation for a specific application. Then, as new models become available, You can compare the existing models based on the same conditions.
The purpose of this paper is to provide guidelines to be considered in the evaluation of video cameras for use in surveillance applications. These applications are those that would be used by the military, police and staff special investigations of evidence or making an electronic collection and generally include viewing distance. Although these guidelines are useful for understanding the major camcorder specifications before making their decisions to buy video camera, we suggest you conduct your own research on models available and, on the basis of these guidelines, choosing the models that are supposed to provide the best performance and conduct their own tests in real situations. You may learn that other factors may be important for your specific application and final decision is a compromise of these other factors.
To control optical image quality is paramount. Camcorder Resolution and sensitivity are key factors to consider, with a variety of related factors, such as image and pixel field of view, the pixel size and frame rate, image stabilization, lens options and the replacement of an objective method of exchange integration, digital zoom and screen resolution user interface, video formats, recording media, manual mode Gain of infrared video compression, external audio input, the display, robustness and video compression.
Camcorder Resolution
Video resolution is affected by many different camcorder specifications. It is well known that high-definition camcorders, provide better resolution than standard definition formats. However, it is important to realize that if the camera is used to store sequences images which are then considered (instead of using the camera to show video output in real time), both in resolution and optical properties of the format recording should be considered in determining the final video resolution. Considered separately, the optical resolution depends not only on the size of detector network but also the image and the pixel field of view. HD recording format also affects the resolution. Finally, there are other factors that the resolution May warrant an examination to determine the final resolution camcorder.
Size of the array of detector:
It seems each camera uses a slightly different image detector. While HD recording format can be 1280×720, 1440×1080 or 1920×1080, image sensors can vary slightly. As the table shows, for selected camcorders midrange, detector array size can vary from single-chip cameras have arrays as large as 1920×1080 (Canon HF-10 and Sony HDRSR11) three blocks of chips with sensors the size of 1440×1080. The physical size of the image sensor varies from camera video to video camera.
Image and Pixel field of view:
As shown in the graph – (referenced in the link above), the combination of physical size of the camera image sensor (eg 1 / 3 ") and its focal length of 50 mm (for example) leads to an image field of view (FOV) is defined as the angle of view from which we get information of the image. There are different angles corresponding to the horizontal And vertical directions as the aspect ratio of the image. Video formats for wide screen, the vertical field of view is 9 / 16 horizontal field of view. All camcorders have a zoom lens whose focal length varies from a wide angle (with the larger field of view angle) to a TV (with the field of view small angle). A smaller field of view results in an image magnification ratio high as would be necessary to display objects small at a distance.
Create small angles narrower image sensors when using the lens of the same focal length. For example, a lens 50 mm provides a horizontal field of view of 5.5 ° and 3.7 ° when used with a 1 / 2 "and 1 / 3" sensor format, respectively. On the basis of variation in the size of the detector and lens focal length, the angular field of view for different cameras varies accordingly. The image field of view can be determine for all cameras based on a simple formula.
The pixel field of view (also known as the instantaneous field of view, or CVI) is a measure of resolution of an imaging system. Although related, the pixel of the image and FOV field of view are different and have a video camera Image narrow field of vision does not necessarily have a corresponding narrow field of view pixel. As shown in the table (see link above), while Camcorders Canon's are smaller and the values of field of view pixel images, the Sony HDR-SR11 has a small field of view FOV pixel Despite an image that is nearly twice larger than the Canon.
A field useful vision calculator can be used to determine values for FOV camcorders particular candidate. Pixel FOV is estimated detection, identification and recognition of the values range from about formats specified object at a fixed distance.
Recording Format:
The difference between the various formats of HD recording is outside the scope of this document. However, the impact recording format in the resolution is essential for the realization of images for surveillance applications and is described here.
As shown in figure (referred to in the first link in article), video cameras standard definition (with a 4:3 aspect ratio) recorded video with 480 horizontal lines per frame, This gives a resolution of 640 x 480. (This is for NTSC. Registered PAL formats with 576 lines per frame provides a resolution of 640×576). In versions of the big screen of standard-definition camera with a 16:9 aspect ratio were also recorded and available with a resolution of slightly larger 720 x 480 (720×576 for PAL versions). Due to limitations of the recording format, which would have been useful to have a high-resolution CCD / CMOS sensor more 720×480 pixels on a video camera NTSC standard definition, except in certain circumstances (such as zoom in for central pixels). However, with the introduction of recording formats for the highest resolution, resolution detectors have greater meaning.
Camcorder sensitivity
High definition video refers to the more standard definition resolution and more often refers to decisions based at 720 lines per frame or 1080 lines / frame. Recording formats can be 1920×1080, 1440×1080 and 1280×720. As a result, are available with 720 or 1080 lines by frame recording formats with a resolution of 1280×720 and 1920×1080 respectively. It is important to understand the recording format for all camcorders in question. If the resolution of the sensor is necessary to fulfill the oversight role, then make sure that the camcorder records in sufficient resolution.
This article was about digital cameras, the previous discussion on the recording format is sufficient to describe the effects on image quality. However, as the integrated video motion, the fact that some cameras record "embedded" video, while others record "progressive" the movie has some importance, especially when the movement is important for the type of surveillance carried out. If not, then the importance of the interrelationship of exploration Progressive versus less important.
Other factors Resolution:
It is worth mentioning that these video cameras using three sensors, the pixels of the breakthrough technology has been used in the horizontal axis to make gradual improvements in sensor resolution using interpolation. This complicates the calculation of the optical resolution of something, but can not be a major factor.
Camcorder Low sensitivity to light is often very important for applications surveillance, especially when the image dusk or dawn, but when you attach the night vision module that intensifies ambient light. Guidelines for the camcorder assessment are listed below. We recommend considering the following factors: the recommended minimum lighting specifications, Objective Lens F-number, the detector pixel size, the availability of the module of vision at night.
As such, the criteria for the comparison of these include: F-lens objective, the number of pixels in size, noise reduction, it is clear that the low light performance as detailed in the list of camera specifications video cameras, because different variables can produce results, although the specifications may be similar.
Therefore, Once you have identified a few different cameras that have the characteristics of interest and the performance you need, it is important to test the lower house in the ability of light.
Recommended Minimum Illumination Specification
Very often, performance specifications are provided in low light on a sheet specifications of the camcorder. They are often described as the sensitivity is "Low Light" or "minimum illumination and the result is expressed as lux. The greater the number of lux is, the better the camera performs in low light. However, due to the details describing how to make these low measurements of light often not provided, it is extremely difficult to compare these figures to compare the different camcorder models from different manufacturers. (What is the reflectivity objects is being viewed? What is the SNR? Image Brightness? etc.). As such it is difficult to use these specifications and not always satisfactory. Obviously, is preferable to test yourself camcorders. Some websites (such as www.camcorderinfo.com target = "_blank">) conduct their own rigorous testing.
Pixel size of detector:
Not only the size of the major network detector, but the physical size detector is also important for several reasons. In most cases, a detector of small physical size (eg, 1 / 6 "format) are more cheap video cameras, while the larger detectors (eg, 1 / 3 "Format) are found in video cameras more efficient. Physically, small detectors need lens, smaller and cheaper to produce cost-compact camcorders. For surveillance applications, an important consideration is to reduce the sensitivity to light with a pixel size. While most pixels generally have a greater sensitivity to light and are higher when the image in low light or night, the larger pixels also translate into a decrease in resolution (in exchange for a lens focal length). In addition, larger pixels, with a table of results in large grids and large glasses. Thus, smaller pixels are often preferable. We have to compare the sensitivity of cameras with smaller pixels, with other camcorders study. The pixel sizes for a variety of digital video cameras are shown in cons table (reference in the first link in the article).
Objective Lens F-Number:
As with the cameras SLR, Lens F-number is very important for low-light sensitivity for a camcorder. All things being equal, a lens with low F-number F1.4 (for example) focuses much of the light from the scene camera sensor sensitive image. A lens with an F-number that is twice as high (F2.8), reaching only 25% of light through, which makes the camera at 25% as sensitive. That's a lot! For compact video camera with an integral objective, sometimes the lens of objective should be designed with a large F relatively high in order to maintain the compact design still offers the desired zoom range. In particular, we note that the F-number increases with time, focal length values slightly. F-digit maximum zoom setting for a variety of digital video cameras are shown in Table attached.
Night Vision Module Availability:
For camcorder to be used to monitor the availability applications a module for night vision can be very important, especially for imaging and night. Camcorders have simply not sensitive sufficient light for the image in these environments. However, target = "_blank"> connect a night vision module, as presented here, the light sensitivity of the camera can be increased to ten F-stops. As is known, the resulting image will be green night vision, in the absence of all colors. However, reasonable images can be produced by stars and the moon. Some of these night vision modules can be viewed by clicking the link above.
Other factors to consider
The evaluation of the cameras for surveillance applications, resolution and sensitivity are generally the main considerations, other factors may merit attention. Some of them are listed below.
Media: "Media" refers to the video store. Many cameras use several different types of media. This The following are the most common types of media and some considerations for surveillance applications:
- MiniDV Tape – These have been used for many years. The disadvantage is the need for forward and back instead of direct access. However, it is known to be very reliable, which are widely available and robust. Furthermore, it is often desirable to have a physical environment with vigilance by video instead of just an electronic version that could easily be lost or mislabeled.
- MiniDVD – Even if the media Family communication can not be as convenient as expected from the DVD often can not be inserted directly into DVD players. Furthermore, recording on the highest quality sometimes results in a much smaller capacity.
- Hard drive (HDD) – The media capacity is generally high (eg 120 GB) with a long record. Backup is important and necessary. Also consider carefully whether the compressed video is used for storage in order to increase available capacity.
- Flash Memory – Memory Flash (like memory semiconductors and smart cards) is very interesting because there moving parts resulting in a compact and efficient. Increasing the capacity of each year.
Image Stabilization:
The camcorder image stabilization is a feature that improves image quality handheld video recordings, such as reducing motion blur video camera. The video camera stabilizer Shake corrects for the raids at telephoto (such as video taken from a moving vehicle) projected onto the camera detector. The stabilizing effect of digital image in general, the video camera movement and use of additional rows and columns on the perimeter of the detector, the movie clip an amount sufficient to stabilize certain types of stroke. Typically, optical image stabilizers, although more expensive, more preferable because it eliminates the uncertainty component of the motion.
Interchangeability of objectives:
Many reduce costs cameras have removable objective lenses. These lenses are compact and highly integrated into the camera body, have a very wide range of focal lengths and even building macro. Normally, the field of view of integration is selected zoom range to reach the desired field of view for most applications. But for even more versatility, higher end camcorders offers a removable lens and a framework for a series of lenses that can be proposed for a change broader applications, including wider viewing angle and telephoto. (See list of mid-range camera lenses removable here). For cameras removable lens, wide angle field of view as telephoto or more values are needed, the adapters are sometimes proposed to change the magnification as desired. But the result is a reduction in optical quality. To control camera, interchangeable lenses can be a great advantage if the increase offered by the camera lens fixed is not sufficient for the desired application. Furthermore, night vision modules that are designed for removable-lens cameras and lens kit the video camera and keep all the functions that the front lens "includes power zoom, auto-iris and image stabilization.
Digital Zoom:
The digital zoom is an important asset to any video camera. It is impossible to evaluate the whole image sensor in the viewfinder resolution video camera or display, digital zoom allows the operator to drill in the viewfinder that might otherwise go unnoticed until the images Digital were analyzed. It is also useful to note that a detector of an array of pixels allows for greater operator for more than a digital zoom camera with a detector having a small size, without the effects of pixelation.
User Interface:
Any camera operator video confirms that access to the functions of a certain importance. Drilling sub-menu after sub-menu to access the routine functions is not desirable to do while in the field.
IR mode:
Some camcorders have a sensitivity to near infrared light to use an illuminator infrared to illuminate the scenes. For various reasons, these illuminators are not applicable to many control situations. On the one hand, light is usually included with the camcorder does not shed enough light for distances of interest. They can be detected by others with most camcorders and CCD cameras.
Manual Gain:
For low light situations, Some camcorders offer a manual gain mode, which allows the user to manually adjust the gain of the video image, in general, increasing to +18 dB. Although grain, for surveillance applications, video images are usually a significant improvement not to purchase or not self-purchased versions.
Shutter speed:
While maintaining the frame rates standard (eg 60 Hz) is not necessary because the observed objects in rapid motion, the frame rate and shutter speed sensor is reduced (by eg for 1 / 3 sec), so that each pixel sensor is integrated into the light for a long time they are exposed. In dark environments, choose the longest time integration may be sufficient to provide an acceptable image for use at dusk or dawn.
External Audio Inputs:
To prevent the occurrence of such a possibility pure geek, it is important to mention that the audio quality and access to external audio input is important for surveillance camera. The microphone does not always work well when taking pictures at a distance or when you need something more directional to filter background noise.
Viewfinder:
In carrying out covert surveillance, the camera viewfinder is sometimes important to keep the screen lighting.
Robustness:
Another important undertaking is the lack of robustness in camera equipment – Switches and controls fragile cameramen stress. When you're in field in potentially dangerous conditions, do not want to play with few controls and LCD panels that come easily to hand.
Price:
Of course, price is always a consideration when assessing the number of video cameras are many models available today. But what these guidelines should prove it very often the most expensive camera can not be the best for specifi c application. Understand what features are most beneficial to your application in considering the price range of camcorders.
Conclusion
Technological improvements in CCD image sensors and CMOS and the introduction of new screen formats and HD recording has led to the introduction of lots of different models of digital camcorders. Guidelines included in the evaluation of video cameras for use in surveillance applications.
For monitoring, optical image quality is paramount. Camcorder resolution and sensitivity are key factors to consider, with a variety factors such as image and the pixel field of view, the pixel size and frame rate, image stabilization, other options lens interchangeability and objective method of integration, digital zoom and the resolution of the screen, the interface user video formats, recording media, manual gain, the infrared mode, video compression, external audio input, the viewer, robustness and video compression.
Although these guidelines are useful for understanding the important specifications of the camcorder before you buy his own camcorder purchase decision, we suggest doing your own research on available models and, on the basis of these guidelines, the choice of models expected to offer the best performance and conduct their own tests in real situations. You can learn that other factors may be important for your specific application and his final decision is a compromise of these other factors.
Disclaimer: We have attempted to provide accurate information. However, We can not accept any responsibility for errors or inaccuracies. If you find errors or need help, Please contact us directly. Thank you.
For more comprehensive White Papers visit our online Knowledge Center.
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