ABSTRACT
Get a digital camera for the exercise of control to use? Now have the technological improvements in CMOS and CCD image sensors and the introduction of new high-definition viewing and recording formats surely led the introduction of many different models of digital cameras. Due to the variety of features and price, it is harder than ever to choose the best digital camcorder. Certain,Some models are better than others in exchange for the application that was designed for the camera and the functions that are needed. Because it introduces so many factors in the selection and new models that are often linked, it is better to provide guidance for the evaluation of the model for a particular application. Then, as new models are available, can be compared with existing models on the basis of the guidelines.
For purposes of thisDocument it is, guidelines should provide for the evaluation of the cameras for use in surveillance applications. These applications are those that would be from the armed forces, police and investigative authorities, staff of the special collection or a new collection of used electronic and include remote viewing in general. Although these guidelines for the understanding of key camera functions before they purchase their camcorders are useful, we recommendHer research on models available and based on these guidelines to select the models that should provide the best performance and run your own tests in real situations. You may be aware that other factors may be important for your specific application, and the final decision is a compromise that these other factors.
To monitor the optical image quality is of paramount importance. Camera resolution and sensitivity are important factors to consider,with a variety of factors such as image and the pixel field of view, pixel size and frame rate, image stabilization, the options for replacement of interchangeable lenses and objective in the integration mode, digital zoom and view the resolution, user interface, video format, audio recordings to win the manual, the infrared mode, video compression, external audio input, the seeker, the robustness and video compression.
Camcorder Resolution
The video resolution is influenced byVariety of different specific camera. And 'well known that high-definition camcorder, a higher resolution than standard definition formats. However, it is important to recognize that when the camera is used for sequences of images that are to be taken into account, records (and not just see your camera's video output in real time), both the optical resolution and recording format should be considered when determining the resolution of the final video. By itself, theoptical resolution depends not only on the size of the detector, but also the image and the pixel field of view. Recording format also affects HD resolution. Finally, there are other factors that led to resolution of May to review to determine the maximum resolution of the camera.
Detector Array Size:
It seems that every camera uses a slightly different image detector. During the recording format is HD 1280×720, 1440×1080, or 1920×1080, ImagingDetectors can vary slightly. As the table shows, for selected mid-range cameras can vary the detector array of the size of single-chip cameras have arrays as large as 1920×1080 (Canon HF-10 and Sony HDRSR11) three blocks with chip detectors as large as 1440×1080. The physical size of the image sensor varies from camera to camera.
Image and pixel Field of View:
As shown in Table disadvantages (see link below), theCombination of the physical size of the image of the camera sensor (eg 1 / 3 ") and the focal length (eg 50mm) to an image field of view (FOV) is the perspective from which the received image information defined. There are different views that the horizontal and vertical direction of the relationship of the image. For video formats on the big screen, the vertical FOV is 9 / 16 of the horizontal FOV. Some camcorders have zoom onif the duration of contact lenses range from wide angle (with the largest angle FOV) to a TV (with small angular FOV). A smaller field-of-view results in a ratio of images at high magnification, very small objects as required in a distance.
Small angle of imaging sensors for the creation of more restricted if used on the lens focal length. For example, a lens of 50 millimeters, provides a horizontal FOV of 5.5 ° and 3.7 °, when used with a 1 / 2 "and 1 / 3" format sensorrespectively. On the basis of the change in the size of the detector and the focal length, field of view angle for different cameras varies accordingly. The image field of view can be set for all cameras on a simple formula.
Pixel FOV (also known as the instantaneous field of view or CVI) is a measure for the resolution of an imaging system. Although related, are different, the pixel in the image FOV and FOV and a narrow FOV camera image may notNarrow field of view pixel. As indicated in the table (see link below), while the Canon camcorders are smaller and the values of the pixels of the image FOV, the Sony HDR-SR11 has a low pixel FOV, although the image FOV is almost twice as high as Canon.
This calculator will FOV can be used to determine the values for the cameras FOV particular candidate. Pixel FOV is calculated that the detection, identification and values in the range of recognition for some specific object created for a particularto achieve.
Recording format:
The difference between the various formats of HD recording is not within the scope of this document. However, the impact of the recording format for the resolution for the performance of imaging for surveillance applications are important and is described here.
As shown in the figure (see link below), standard-definition camcorders (with a ratio 4:3) recorded video with 480 horizontal lines per frame, which offers a resolution of 640 x 480.(This is registered for NTSC. PAL with 576 lines per picture has a resolution of 640×576). Widescreen versions of these standard-definition camcorder with a ratio of 16:9 are also available, and capturing images with a resolution) slightly higher at 720 x 480 (720×576 for PAL versions. Due to limitations of recording format, it would be useful for a high resolution CCD / CMOS sensor, 720×480 pixels than a standard-definition NTSC video camera, with the exceptionsee under certain circumstances (eg, the zoom on the central pixel). However, with the introduction of higher resolution formats for recording, resolution detectors a higher meaning.
Camcorders sensitivity
High-definition refers to the video at a lower resolution than standard definition and in most cases refers to the resolution to 720 lines per frame or 1080 lines per picture is based. Recording formats 1920×1080, 1280×720 and 1440×1080. Therefore, they areAvailable with 720 or 1080 lines per image recording formats with a resolution of 1280×720 and 1920×1080, respectively. It is important to understand the recording format for all the cameras in question. If the resolution of the sensor is necessary to fulfill the monitoring function, make sure that the camcorder takes in a sufficient resolution.
In this White Paper has been on digital cameras, has been sufficient debate on the format of the records todescribe the impact on image quality. However, since video takes the movement, the fact that some cameras are distinguished from interlaced video, while other records "progressive" video has some importance, especially when the movement is important for the type of controls. If not, then the amount of interlace vs. progressive scan is less important.
Other factors Resolution:
It is noteworthy that in these cameras that usethree sensors, the pixel technology gap was horizontal to make incremental improvements to the resolution of the sensor with interpolation. This complicates the calculation of optical resolution, can be a bit ", but not be an important factor.
Camcorder low light sensitivity is usually of crucial importance for surveillance applications, especially when imaging at sunrise or sunset, but also in creating a module for night vision, which amplifies the ambient light. GuidelinesCamera for the evaluation are listed below. It is recommended that the following factors: the minimum intensity individual counseling Lens F-number to consider, the size of the pixels of the detector, the availability of night vision module.
As such, the criteria for the comparison is this: is the front lens F number, pixel size are noise reduction, it is clear that the performance of low-light conditions, as indicated in the list of specifications as to produce different cameras, camcorders capabledifferent results, even though the specifications may be similar.
So if you have a variety of different cameras that can identify the properties of interest and the required performance, it is important to test the camera in low light capabilities.
Recommended Lighting Specification:
Very common in low-light performance specifications are given on a piece of camera provided. They are generally described as light or lowSensitivity "or" minimal lighting and the result is expressed in lux. Over the lux rating, the better will the camera in low light conditions. Due to data describing how these measures are often made poor lighting conditions are not possible and "very difficult to compare these data to compare the different camera models from different manufacturers. Should (be what is displayed, the reflectivity of the objects are and what is the SNR? brightness of the image? complement, etc.).such, the use of these data is difficult and often unsatisfactory. And to prefer 'natural, even at the sample camcorder. Some sites (like camcorderinfo.com) conducted its own rigorous test.
Detector pixel size:
Not only the size of the detector important, but the physical size of the detector is also important for a number of reasons. In most cases, a detector of small physical size (eg 1 / 6 "size) are less camcorders, whilelarger detectors (eg 1 / 3 ") are more cameras. Physically detectors of small businesses need to wear glasses, smaller and cheaper compact cameras, because the cost is. For surveillance applications, an important consideration that the sensitivity decreases with the size of the pixels. Although larger pixels generally have a higher sensitivity to light and are larger when imaging in low light or at night, the larger pixels also translate into reduced resolution (in exchange forincluding the focal length). And the more pixels, with a large table to a variety of important goals. Thus, the smaller pixels are often preferable. We have to be able to compare the sensitivity of the cameras with smaller pixels, studied with other camcorders. The pixel size for a range of digital cameras are shown in Table disadvantages (see link below).
Lens F-Number:
Like the SLR, Lens F-number is extremely important for aCamera low light sensitivity. Everything else equal, a lens with a low R-F1.4 (eg number), dedicates a large part of the light from the scene image sensors sensitive camera. A lens with an F-number) twice as fast (F2.8, an increase of only 25% of the light from what makes the camera 25% sensitive. That's a lot! For the compact camera with integrated lens, sometimes the front lens with a large F should be designed to maintain a relatively high numbercompact design, a whole series of desired zoom offer. In particular, we note that some of the F-number increases, the values of the focal length. F-digit maximum zoom setting for a series of digital cameras are shown in Table disadvantages (see link below).
Night Vision Module Availability:
For cameras used for monitoring, the availability of a module for night vision is very important, especially for imagingDistance and the night. Cameras just do not have the sensitivity to enough to get a imaging in these environments make the light. However, by adding a module for night vision devices, such as those which appear http://www.electrophysics.com/night-vision on our site, the camera's light sensitivity can be increased up to ten F-stop. As is known, the resulting image Night vision green, in the absence of all colors. But the images can be produced in adequate light from the stars and the moon. Some of theseForms for night vision can be viewed by clicking on the link below.
Other factors to note
In assessing the cameras for surveillance applications, the resolution and sensitivity are usually the most important considerations, other factors, particular attention should be paid. Some of them are listed below.
Media: "Media" refers to the place where to save the video. Many cameras use different types of media. The following are the most common types of media and some considerations areApplications for monitoring:
MiniDV tape – have proved successful for many years. The disadvantage is the need to fast forward and rewind, rather than direct access. However, they are known to be very reliable, are widespread and robust. Moreover, it is often convenient to have a physical medium, with video surveillance and not to copy a single screen, which could easily be lost or misunderstood.
MiniDVD – Although the family to support, may no longer comfortable as aWaiting for the DVD can not often be directly inserted into the DVD. Also, the recording quality often leads to a much smaller capacity.
Hard drive (HDD) – These are generally in favor of large capacity (eg 120 GB) with a record time. Backup is of course important and necessary. Also make sure that the compressed video is used to increase the storage capacity available.
Flash memory – flash memory (such as firmMemory and memory card) is very interesting because there are no moving parts resulting in a compact design and efficient. The ability to increase every year.
Image Stabilization:
The image stabilization function is improved camera, the picture quality for video recordings of the hand, reducing blur caused by camera shake. Stabilizer corrects camcorder shake instantly, so that the attack on Telecommunications (like the video from a moving vehicle are spent)smooth and regular. The image stabilizer can design optical or digital. The optical image stabilizer usually manage a prism to the image projected onto the camera detector to stabilize. The digital image stabilizer usually means that the camera's movement and use of the additional rows and columns on the periphery of the detector, images of moving a quantity sufficient to stabilize certain types of movements. Typically, optical image stabilizer, but expensiveare preferable, because it is better to conceal the movement removed.
Interchangeable:
Many cameras are not cheap removable lenses of objectives. These lenses are compact and highly integrated into the body of the camera, have a wide range of focal lengths and macro functions. Normally, the field of vision of the integration of the zoom is selected to achieve the desired image area for most applications. For more flexibility, more demandingCameras with a lens and a removable frame so that a series of lenses can be used for a wider range of applications, including wider viewing angle and telephoto available. (See the list of mid-range cameras with detachable lens here). For non-detachable lens cameras are so wide-angle or telephoto lens FOV values are most needed, the adapters are sometimes proposed to change the magnification as you want to. But the result is a decrease in optical quality. For the surveillance cameraLenses can be a great advantage if the objective magnification by fixed cameras will be granted, is not sufficient for the desired application. Also, the forms of night vision cameras, which are suitably designed with a removable lens to the lens and camera, and keep all the functions that the front lens "including motorized zoom, auto iris and image stabilizer.
Digital Zoom:
Digital zoom is an important asset for any camera. Why can notestimate the image sensor resolution viewfinder of the camera or on a poster, digital zoom, enabling the operator to view the details of the viewfinder, which would otherwise go unnoticed until the digital images were analyzed then go. It is also important to note that a detector made of a number of larger pixels, the operator of more than one zoom digital camera with a detector with a small size without the effects of pixelation can.
Interface:
Each camera confirmed that access to some features of importance. Drilling sub after sub-menu to the routine access is not a desirable thing, while in the field do.
IR mode:
Some cameras have a sensitivity to the near infrared using an infrared illuminator to illuminate the scene. For various reasons, these beacons are not for the monitoring of manySituations. On the one hand, the lighting is usually the camera is not enough to mark the distances of interest. They can also by others with more cameras and CCD cameras are recognized.
Manual Gain:
In low light conditions, some cameras offer manual gain mode, the user manually makes the gain of the video image to adjust normally to 18 dB. Although grainy, surveillance applications, video –Pictures are usually a significant improvement compared to non-vested or not even buy music.
Shutter Speed:
While maintaining the standard frame rates (eg, Hz 60) is not necessary, since the observed fast moving objects, the frame rate and shutter speed sensor will be reduced (eg, 1 / 3 sec), so that each pixel of the sensor integrate light over a longer period, which they are exposed. In dark environments, the selection ofThe more integration in May acceptable enough to give a usable image at dusk or dawn.
External audio inputs:
To prevent the occurrence of such a perspective of pure geek, it is important to remember that the audio quality and access to external audio input for video surveillance is important. The microphone does not always work well when shooting from a distance, or if you have something more directional for filtering the airNoise.
Viewfinder:
If you covert surveillance with a video camera viewfinder is sometimes necessary to prevent the illumination of the monitor.
Durability:
Another compromise is a serious lack of robustness in photographic equipment – switches and controls, the fragile Videographers stressful. If you are on the ground under the conditions that are potentially dangerous, you do not want to play withfew controls and LCD panels, which come easily to hand.
Price:
Of course, the price is always a consideration when assessing the number of cameras are many models now available. But what of these guidelines was to show that very often the most expensive camera can not be better for a particular application. Understand what are the features most beneficial to the application in view of the camera price range.
Conclusion
TechnologyImprovement of CCD and CMOS image sensors and the introduction of new high-definition viewing and recording formats have led to the introduction of various models of digital cameras. Guidelines were provided for the assessment of video cameras for use in surveillance applications.
To monitor the optical image quality is of paramount importance. Camera resolution and sensitivity are important factors to consider, with a variety of interrelated factors, such as images andPixel field of view, pixel size and frame rate, image stabilization, the options for replacement lenses and an interchangeable lens, integrated mode, digital zoom and the resolution of the screen user interface, video format, recording media, manual gain control, infrared, video compression mode external audio input, the viewfinder, robustness, and video compression.
Although these guidelines are for the understanding of the important camera functions, before deciding on the usefulness of a camcorder purchaseWe propose your own research on models available and based on these guidelines, the selection of models that should provide the best performance and run your own tests in real situations. You may be aware that other factors may be important for your specific application, and the final decision is a compromise that these other factors.
To see all figures and the examples cited in this article, click here
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