Abstract
Looking for a digital camera for use in surveillance? Now, technological improvements in CCD and CMOS image sensors and the introduction of new high-definition display, and recording formats certainly led to the introduction of several digital camera models. Due to large differences in features and price ranges, it is more difficult than ever to find the best digital camcorder. Of course, some models may be better thanothers, taking into account the specific application for which the camera was designed and functions that are necessary. Because there are so many factors to take into a selection, and because new models are introduced it is often better guidelines are useful for evaluating the models for a particular application involved determined. Then, as new models are available, they may be based on existing models are compared with the same guidelines.
The purpose of this work is to provide guidelinesthat should be in the evaluation of video cameras for surveillance applications. These applications are those that would be used by military forces personnel, enforcement and special investigative methods for gathering evidence or performing Electronic News Gathering and usually include a remote display. While this information helpful in understanding the specific camera is first important to have your camera purchase decision, you should perform their own researchmodels and based on these guidelines, you can choose the models that are expected to provide the best performance and test their own real-life situations. You can learn that other factors may be important for your specific application and the final decision is a compromise between these other factors.
For monitoring the optical quality of the image is of paramount importance. Camera resolution and sensitivity are the main factors to consider, with a variety of relatedFactors such as image and the pixel field of view, the pixel size and frame rate, image stabilization, optional lenses and interchangeable lens options, integration mode, digital zoom and the resolution of the screen, the user interface, video formats, recording media, manual gain, the infrared mode, video compression, audio inputs, front sight, robustness and video compression.
Camera resolution
The video resolution is influenced by a variety of different camera features.And 'well known that high-definition cameras offer higher resolution than standard-definition formats. It may be noted, however, important that when the camera is used for sequences of images that are then to be considered (to be instead of the camera is simply displayed on the video output in real time) record is the optical resolution and format Registration must be like in determining the ultimate resolution. Considered separately, depends not only on the optical resolution ofArray size of the detector, but also the image and pixel field of view. HD recording format also affects the resolution. Finally, there are other factors that warrant consideration, the resolution can in order to determine the final resolution camera.
Detector Array Size:
It seems that any camcorder uses a slightly different imaging detector. While the format of HD recording can be 1280x720, 1440x1080 or 1920x1080, imaging detectors can vary a bit '. As shown in the table for aSelection of mid-range array detector size cameras can single-chip cameras with arrays as large as 1920x1080 (Canon HF-10 and Sony HDRSR11) three-chip detectors vary with blocks as large as 1440x1080. The physical size of the imaging detector also varies from camcorder to camcorder.
Picture and Pixel Field of View:
As in the attached table (refer to the link below), the combination of the physical dimensions of the camera's imaging detector (eg, 1 / 3 ") shownand the focal length of the objective lens (eg 50mm) results in an image field of view (FOV), which is defined as the angle from which they received information image is defined. There are isolated corner which corresponds to the horizontal and vertical directions, depending on the aspect ratio. For wide-screen video formats, the vertical field of view 9 / 16 of the horizontal FOV. Some camcorders have zoom lenses, where the range of focal lengths from wide angle (with the largest angleFOV) of a telephoto position (with the smallest angle FOV). A smaller field of view leads to a higher magnification image, as would be necessary to see small objects at a distance.
Imaging detectors produce a smaller viewing angle more closely, when used with the same lens with fixed focal length. For example, a 50 mm lens provides a horizontal field of view of 5.5 ° and 3.7 ° when used with a 1 / 2 "and 1 / 3" sensor size, respectively. Based on the change in the size of the detector and focal lengths, l 'Field of view for different cameras varies accordingly. The FOV image can be determined for each camera to a simple formula.
(Also known as the IFOV or IFOV), the FOV pixel is a measure of the resolution of an imaging system. Although related, are the image pixels and FOV FOV and a clear narrow FOV camera with the image is not necessarily a corresponding pixel narrow field of view. As in the table (refer to the link below), while the CanonIt's the smallest camcorder is image and pixel values of the VOC Sony HDR-SR11, despite a small field of view FOV of a pixel of the image that is almost twice as large as the Canon.
A FOV calculator helpful in determining the values of VOC for some cameras candidates. Pixel FOV is calculated as the detection and identification of the recognition of a certain specified range of size of objects within a certain distance.
Recording format:
The difference between the different HDRecording formats is beyond the scope of this document. However, the influence of the recording format on the critical resolution on the quality of the images for surveillance applications and is described here.
As shown in the figure (the reference link below), standard-definition camera (with a ratio of 4:3) video at 480 horizontal lines per frame, resulting in a resolution of 640 x 480 recorded (This is for NTSC. Format PAL with 576 lines per frame, resulting in resolution of the recorded640x576). Wide-screen versions of these standard-definition camcorder with an aspect ratio of 16:9 were available and recorded with some great resolution of 720 x 480 (720x576 for PAL versions). Because of the recording format, would not make sense, high-resolution CCD / CMOS detector larger than 720x480 pixels in NTSC standard definition video camera, except in certain circumstances (such as zoom in view of the central pixel) to have. But with the 'Introduction of high-resolution recording formats, higher resolution detectors sense.
Camcorders sensitivity
High-definition refers to video with a higher resolution than standard definition, and most commonly refers to decisions of both 720 lines / frame or 1080 lines / frame-based. Recording formats can be 1920x1080, 1440x1080 and 1280x720. Consequently, available with either 720 or 1080 line formats for recording images with a resolution of 1280x720 and 1920x1080respectively. It 'important to understand the recording format for video cameras in question. If the resolution of the sensor is necessary to perform the monitoring function, then make sure that the camera records in sufficient resolution.
It would have been in this white paper on digital cameras, the discussion above the recording format would have been sufficient to describe the effect on image quality. Since motion detection, the fact that some camcorders recordRecord "interlaced" video, while other video "progressive" has a certain significance, especially if exercise is important, the type of monitoring is carried out. Otherwise, the relevance of interlaced vs. progressive scan is less important.
Other factors Resolution:
It is worth mentioning that the cameras use three sensors, pixel-shift technology in the horizontal axis was used to make incremental improvements to the resolution of the sensorInterpolation. This complicates the calculation of the optical resolution of something, but can not be a primary factor.
Low light sensitivity camera is usually of paramount importance to surveillance applications, especially in the figure in the shadows, but also the application of a form of night vision, increases in ambient light. The guidelines for the evaluation camcorder are listed below. We recommend starting a review of the following factors: The recommended minimum illumination specific,Diameter lens, F-number, size of the pixel detectors, night vision modules available.
As such, but the criteria under which the comparison includes the following: Lens F-number, pixel size, the suppression of electronic noise, it is clear that performance in low light conditions, as the list of specific cameras because multiple cameras in can produce different results, even if the specifications are similar.
Therefore, when once you have identified a few different cameraproperties of interest and the power you need, it is important to test the low light camera capabilities.
Recommended Specifications Minimum illumination:
Often, performance in low light camera on a sheet specifications. These are usually described as "low sensitivity to light" or "low light" and the result is expressed in lux. The lower the lux rating, the better the camera takes in dim light. However, sinceDetails describe how those in low-light measurements are made is not usually provided, it is extremely difficult to compare these numbers when comparing different models of camera from different manufacturers. (What is the assumed reflectivity of the objects displayed, what is the signal to noise ratio? Brightness? Etc..). As such, the use of these guidelines are often complex and unsatisfactory. Of course it is best to test the same camera. Some sites (such ascamcorderinfo.com) lead them, very severe tests.
Detector pixel size:
Not only the size of the array detector is important, but the physical size of the detector is also important for a number of reasons. In most cases, revealing small physical quantities (eg 1 / 6 "size) are found in less expensive video cameras, while larger detectors (eg 1 / 3" format) camcorder in a higher power can be found. Physically small detectors require smaller, less expensive and slow results in compactness,cameras at low cost. For surveillance applications, is an important consideration that the sensitivity decreases with pixel size. While larger pixels generally have more sensitivity to light and are larger when imaging in low light or at night, the more pixels in a decrease in resolution (in consideration of a particular focal length) result. With larger pixels wide range lead to large arrays and large glasses. So smaller pixels are often preferable. It shouldComparison pulled the camera's sensitivity with smaller pixels into account with other cameras. Pixel sizes for a variety of digital cameras in the table attached (see link below).
Lens diameter, F-number:
As with SLR cameras, the lens F number is very important to have a low light sensitivity camera. All other things being equal, the focus of a lens with a low f-number (eg F1.4), plenty of light-sensitive camera from the sceneImaging detector. A lens with an F number that is twice as high (2.8) only 25% of light to pass through, so that the camera is 25% as sensitive. That's a lot! Be developed for compact cameras with lenses built, sometimes the lens with a relatively high R-series, to maintain consistency still deliver the desired zoom area. In particular, we find that the F-number increases slightly the values of focal length. F-number at the maximum zoomSetting for a series of digital cameras in the table attached (see link below).
Night Vision Module Availability:
Be used for surveillance camera applications, may be the availability of a form of night vision is of great importance, particularly for imaging at a distance and at night. Cameras are not just enough to allow the light sensitivity for imaging in these environments. But with the addition of a night vision module, as shown in ourHttp: / / www.electrophysics.com / Night Vision Web site, the camera's light sensitivity up to ten F-stop. As is known, the resulting images are for night vision green, all colors have disappeared. But, it is reasonable images in starlight and moon are made. Some of these forms of night vision can be viewed by clicking on the link below.
Other factors to consider
In evaluating applications for surveillance cameras have the resolution and sensitivity, in general,Primary considerations may, other factors deserve attention. Some of them are listed below.
Media: "Media" refers to itself, where the video can be stored. Many camcorders use a variety of media types. 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 to rewind before and, instead of direct access. However, they are known to be quite reliable,They are widespread and robust. In addition, it is often convenient to physical media with surveillance footage instead of a soft copy only could easily be lost or mistakenly. MiniDVD - Even if a family support, perhaps not so convenient as often as the DVD can not be directly used in DVD players expected. Moreover, the inclusion in the highest quality at times to a much lower capacity. Hard Disk Drive (HDD) - These are generally highThe average capacity (eg 120 GB) with long exposure times. Backup is of course important and necessary. Also note carefully when the compressed video is used for storage, to increase the available capacity. Flash Memory - flash memory (such as solid state memory and memory card) is very interesting because there are no moving parts in a compact and efficient. Capabilities are increasing every year.
Image Stabilization:
The image stabilization is a cameraFeature helps to improve the quality of the images during the hand-Video, reduces blurring caused by camera movement. The stabilizer corrects camcorder shake instantly, so you're shooting handheld (as recorded video from a moving car) to telephoto lens are smooth and uniform. This image stabilizers can be either optical or digital design. Manipulating optical image stabilizers usually a prism lens to stabilize the image when projected onto the camera sensor. Digital image stabilizationin the sense motion control and stabilize the camera by taking advantage of other rows and columns of the size of the detector, moving the image in a reasonable amount of some types of movement. Normally, the optical image stabilizers, although more expensive, is preferred because it best to remove the motion blur.
Interchangeable Lens:
Many cameras have a lower cost non-removable lenses. These lenses are compact and highly integrated inBody of the camera has a zoom range of very large, and the ability also macros. Normally, the field of view was selected the built-in zoom, to get the FOV range for most applications the desired effect. However, increases flexibility, offering high-end camcorder with a detachable lens and a bayonet, so that a series of lenses for a wider variation of applications, including the largest and most remote corner of the display can be offered. (See a list of mid-range camcorder with interchangeable lenses here). Fornon-removable lens, if larger or more tele-angle FOV values are required adapters are sometimes offered to change the magnification as desired. But the result is a decrease in optical quality. For authors of video surveillance can change lenses to be a great advantage when the magnification is offered by fixed lens cameras, not enough for the desired application. In addition, mounting the modules developed for night vision lens removable media between the lens andCamera and maintain all the features of the lens', including motorized zoom, auto-iris and image stabilization.
Digital Zoom:
Digital zoom is an important feature for any camera. Since it is not possible, all the imaging detector, the resolution on the camera viewfinder or display digital zoom allows appreciating provider for details on the viewfinder, which would otherwise have gone unnoticed, were subsequently analyzed for digital images. It is also usefulThey note that a detector with an array of pixels and digital zoom More players more, as you carry a camera with a detector smaller without the effects of pixelization.
User Interface:
Each camera operator confirms that the accessibility features can be of some importance. Drill-down through sub-menus to access sub-menu to perform routine functions is not a desirable thing to do while in the area.
IR mode:
Some cameras have a sensitivity ofNear-infrared allows the use of an infrared lamp to illuminate the scene. For a variety of reasons, these lamps are not suitable for many monitoring situations. Date For one thing, usually in the spotlight with the camera is not in lighting design suitable distances of interest. In addition, they can be captured with most other cameras and CCD cameras.
Manual Gain:
For low light situations, some cameras offer a manual mode gainthat allows the user to manually adjust the gain in video picture, typically up to +18 dB. Although grainy, for surveillance applications, video images is usually a marked improvement has not won or even car-derived versions.
Shutter speed:
If you keep the standard frame rate (eg 60Hz) is not necessary, since the objects under observation does not move quickly, the frame rate and shutter speed detector can be reduced (eg 1 / 3 sec), sothat each pixel of the light sensor is integrated on a longer time, which they are exposed. In dark environments, the selection of the longer integration time is acceptable enough to provide a usable image at dusk.
External audio inputs:
At the onset of sounds like a pure optical to prevent outsiders, it is important to note that the audio quality and access to external audio inputs important for authors of video monitoring. The built-in microphonenot always good at taking pictures from afar, or if you need something more directional filter out ambient noise.
Viewfinder:
In carrying out covert surveillance, with a camcorder's viewfinder is sometimes important to prevent the light from the LCD brighter.
Strength:
Another compromise is the serious lack of robustness in camera hardware - causing the switches and controls brittle, stress videographer. If you arethe range of potentially dangerous conditions, do not want to be the game with a few controls and LCD panels, which removed too easily.
Price:
Of course the price is always a consideration when evaluating the many, many models of cameras available today. But what should these guidelines show that very often the most expensive camera can not be the best for a particular application. Understand what features are best suited to your application for consideration ofCamera price range.
Completion
Technological improvements in CCD and CMOS image sensors and the introduction of new high-definition display, and recording formats have led to the introduction of several digital camera models. Guidelines were provided in the evaluation of video cameras for surveillance applications.
For monitoring the optical quality of the image is of paramount importance. Camera resolution and sensitivity are the main factorsto consider, with a variety of factors, including the image and the pixel field of view, the pixel size and frame rate, image stabilization, optional lenses and interchangeable lens options, integration mode, digital zoom and display resolution, user-friendly interface, video formats, recording media, manual gain, the infrared mode, video compression, audio inputs, targeted compression, robustness and video.
While these are useful references for understanding important CamcordersSpecifications before buying your decision camcorder to make their research available models and on the basis of these guidelines, you can choose the models that are expected to provide the best performance and test their own in real life situations. You can learn that other factors may be important for your specific application and the final decision is a compromise between these other factors.
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