Abstract
Looking for a digital camcorder for use in performing surveillance? Well, technology improvements in Ccd and Cmos image sensors as well as the introduction of new high definition display and recording formats have categorically resulted in the introduction of lots of separate digital camcorder models. Because of the wide divergence in features and price points, it's more difficult than ever to agree the optimal digital camcorder. Certainly, some models will be great than others in notice of the exact application for which the camcorder is intended and the features that are required. Because there are so many factors involved in manufacture a option and since new models are frequently introduced, it's best to provide guidelines beneficial when evaluating models intended for a exact application. Then, as new models become available, they can be compared to existing models based on the same guidelines.
The goal of this paper is to provide guidelines that should be determined when evaluating camcorders for use in guard applications. These applications are those that would be used by military, law enforcement and extra investigative personnel for gathering evidence or performing electronic news gathering and regularly contain viewing at a distance. While these are beneficial guidelines for insight foremost camcorder specs, prior to manufacture your own camcorder buy decision, we propose that you achieve your own investigate of ready models and, based on these guidelines, agree those models that are expected to deliver the best execution and achieve your own tests under real-life situations. You may learn that other factors may be foremost to your exact application and that your final decision is a compromise of those other factors.
For surveillance, visual image ability is of highest importance. Camcorder resolution and sensitivity are the original factors to consider, with a variety of linked factors such as image and pixel fields-of-view, the pixel size, as well as the frame rate, image stabilization, alternative lens options and lens interchangeability, integration mode, digital zoom and display resolution, user interface, video formats, recording media, by hand gain, infrared mode, video compression, external audio inputs, viewfinder, robustness, and video compression.
Camcorder Resolution
Video resolution is affected by a variety of separate camcorder specifications. It is well known that high definition camcorders deliver higher resolution than suitable definition formats. However, it is foremost to perceive that if the camcorder is used to report image sequences that are later to be viewed (rather than using the camcorder just to view the video production in real time), both the visual resolution and the recording format must be determined in determining the extreme video resolution. determined separately, the visual resolution depends not only on the detector array size but also the image and pixel field-of-view. Hd recording format also affects resolution. Finally, there are other resolution factors that may certify notice in order to determine the extreme camcorder resolution.
Detector Array Size:
It seems that every camcorder uses a slightly separate imaging detector. While the Hd recording format can be 1280x720, 1440x1080 or 1920x1080, the imaging detectors may vary quite a bit. As shown in the table, for a option of mid-range camcorders, detector array sizes can vary from single chip cameras having arrays as large as 1920x1080 (Canon Hf-10 and Sony Hdrsr11) to three-chip blocks having detectors as large as 1440x1080. The corporal size of the imaging detector also varies from camcorder to camcorder.
Image and Pixel Field-of-View:
As shown in the with chart (reference at link below) the compound of the corporal size of the camcorder's imaging detector (for example 1/3") and the focal length of its objective lens (for example 50mm) supervene in an image field-of-view (Fov) that is defined as the angle of view from which image facts is received. There are detach angles corresponding to the horizontal and vertical directions depending on the aspect ratio of the image. For wide screen video formats, the vertical Fov is 9/16 of the horizontal Fov. All camcorders have zoom lenses where the focal length varies from a wide angle position (with the largest angular Fov) to a telephoto position (with the smallest angular Fov). A smaller field-of-view results in a higher image magnification as would be required to view small objects at a distance.
Smaller imaging detectors generate narrower angles of view when used on the same focal length lens. For example, a 50 mm lens delivers a horizontal Fov of 5.5° and 3.7° when used with a 1/2" and 1/3" format detector, respectively. Based on the divergence of detector sizes and lens focal lengths, the angular field of view for separate camcorders varies accordingly. The image Fov can be determined for any camcorder based on a uncomplicated formula.
The pixel Fov (also known as the instantaneous field of view, or Ifov) is a quantum of the resolution of an imaging system. Though related, image Fov and pixel Fov are unavoidable and a camcorder having the narrow image Fov does not necessarily have a corresponding narrow pixel Fov. As shown in the table (reference at link below), while the Canon camcorders have the smallest image and pixel Fov values, the Sony Hdr-Sr11 has a small pixel Fov despite an image Fov that is nearly twice as wide as those for Canon.
A handy Fov calculator can be used to determine the Fov values for unavoidable candidate camcorders. Pixel Fov is also calculated as are detection, identification and recognition range values for unavoidable specified object sizes at a specified distance.
Recording Format:
The divergence in the middle of the separate Hd recording formats is beyond the scope of this white paper. However, the impact of recording format on resolution is principal to imaging execution for guard applications and is described here.
As shown in the frame (reference at the link below), suitable definition camcorders (with a 4:3 aspect ratio) recorded video with 480 horizontal rows per frame giving a resolution of 640 x 480. (This is for Ntsc formats. Pal formats recorded with 576 rows per frame giving a resolution of 640x576). Wide screen versions of these suitable definition camcorders with a 16:9 aspect ratio were also ready and recorded with slightly larger resolution of 720 x 480 (720x576 for Pal versions). Because of the limitations of the recording format, it would not have been beneficial to have a high resolution Ccd/Cmos detector larger than 720x480 pixels in a suitable definition Ntsc camcorder except under unavoidable circumstances (like zooming in to view central pixels). However, with the introduction of higher resolution recording formats, higher resolution detectors make sense.
Camcorder Sensitivity
High definition refers to video having higher resolution than suitable definition and most ordinarily refers to resolutions based on either 720 rows/frame or 1080 rows/frame. Recording formats can either be 1920x1080, 1440x1080 and 1280x720. Consequently, are ready with either 720 or 1080 rows per frame recording formats having a resolution of 1280x720 and 1920x1080 respectively. It is foremost to understand the recording format for any camcorder under consideration. If the full sensor resolution is principal to achieve the guard function, then make sure that the camcorder records in sufficient resolution.
Had this whitepaper been about digital still cameras, the above argument of recording format would've been sufficient to delineate the effects on image quality. However, since video incorporates motion, the fact that some camcorders report "interlaced" video while others report "progressive" video has some relevance, particularly when petition is foremost to the type of guard being performed. If not, then the relevance of interlace vs. Progressive scan is less important.
Other Resolution Factors:
It's worth mentioning that in those camcorders that use three sensors, pixel shift technology has been employed in the horizontal axis to make incremental improvements to the sensor resolution by using interpolation. This complicates the calculation of visual resolution somewhat, but may not be a original factor.
Camcorder low-light sensitivity is regularly of original importance for guard applications, particularly when imaging at dusk or dawn, but also when attaching a night vision module that intensifies ambient light. The guidelines for camcorder appraisal are listed below. We propose a delineate of the following factors: the Recommended Minimum Illumination Specification, Objective Lens F-number, Detector Pixel Size, Night vision Module availability.
As such, but criteria enabling the comparison of these including: objective lens F-number, pixel size, electronic noise reduction, It is apparent that low-light execution as detailed on the list of the camcorders specifications because separate cameras can yield varying results, even though the specifications may be similar.
Consequently, once you've identified a few separate camcorders that have the features of interest and the execution that you require, it is foremost to test the camcorder's low-light capabilities.
Recommended Minimum Illumination Specification:
Quite often, low-light execution specifications are in case,granted on a camcorder's specification sheet. These are regularly described as either "low light sensitivity" or "minimum illumination" and the supervene is given in lux. The lower the lux rating, the great the camcorder performs in low light. However, because the details describing how these low-light measurements are made is not often provided, it is highly difficult to correlate these figures when comparing separate camcorder models from separate manufacturers. (What's the assumed reflectivity of the objects being viewed? What's the signal-to-noise ratio? Image brightness? etc.). As such, use of these specifications is involved and not often satisfying. It is obviously best to test the camcorders yourself. Some websites (such as camcorderinfo.com) achieve their own very truthful tests.
Detector Pixel Size:
Not only is the detector array size important, but the corporal size of the detector is also foremost for a number of reasons. Most often, small detector corporal sizes (such as 1/6" format) are found in less expensive camcorders while larger detectors (e.g. 1/3" format) are found in higher execution camcorders. Physically small detectors need small, less expensive lenses and supervene in compact, lower cost camcorders. For guard applications, an foremost notice is that light sensitivity decreases with pixel size. While larger pixels in normal have more light sensitivity and are excellent when imaging in low light or at night, larger pixels also supervene in a decrease in resolution (in notice of a single focal length lens). Also, larger pixels with large array sizes supervene in large arrays and large lenses. So, smaller pixels are often preferable. One should correlate the sensitivity of camcorders with the smallest pixels with other camcorders being considered. Pixel sizes for a variety of digital camcorders are shown in the with chart (reference at link below).
Objective Lens F-Number:
As with Slr cameras, lens F-number is highly foremost to a camcorder's low light sensitivity. All other things being equal, a lens with a low f-number (such as F1.4) focuses much of the light from the scene onto the camcorder's sensitive imaging detector. A lens with an F-number that is twice as high (F2.8) will pass only 25% of the light through it, manufacture the camcorder 25% as sensitive. That's a lot! For contract camcorders with integral lenses, sometimes the objective lens must be designed with a relatively high F-number in order to withhold the contract institute yet deliver the desirable zoom range. In particular, one finds that the F-number at the longer focal length values increases slightly. F-numbers at the maximum zoom setting for a variety of digital camcorders are shown in the with chart (reference at link below).
Night vision Module Availability:
For camcorders to be used for guard applications, the availability of a night vision module can be quite important, particularly for imaging at a length and at night. Camcorders naturally do not have sufficient light sensitivity to enable imaging in these environments. However, by attaching a night vision module such as those shown on our site at http://www.electrophysics.com/night-vision, the light sensitivity of the camcorder can be increased by up to ten F-stops. As is well known, the resulting night vision images will be green, absent of all color. But, inexpensive images can be produced in starlight and moonlight. Some of these night vision modules can be seen by clicking on the link below.
Other Factors To think
In evaluating camcorders for guard applications, resolution and sensitivity are regularly the original considerations, other factors may deserve attention. Some of these are listed below.
Media: "Media" refers to where the video will be stored. Many camcorders use several separate media types. The following are the coarse types of media and some considerations for guard applications:
MiniDv Tape - These have been used for many years. The downside is the need to fast forward and rewind rather than direct access. However, they are known to be quite reliable, they are widely ready and rugged. In addition, it is often favorable to have corporal media with guard footage rather than a soft copy only which could more categorically be misplaced or mislabeled.
MiniDvd - Though a familiar media, it may not be as favorable as one expects since the Dvd often cannot be directly inserted into Dvd players. Also, recording in the highest ability sometimes results in significantly lower capacity.
Hard Disk Drive (Hdd) - These are ordinarily high capacity media (e.g. 120 gigabytes) with long report times. Backup is obviously foremost and necessary. Also note determined if compressed video is being used for warehouse in order to increase the ready capacity.
Flash Memory - Flash memory (such as solid state memory and memory cards) is very animated since there are no animated parts resulting in a contract and effective design. Capacities are increasing every year.
Image stabilization:
Image stabilization is a camcorder highlight that helps improve image ability during hand-held video recordings, reducing blur due to camcorder motion. The stabilizer at once corrects camcorder shake so that hand held shots at full telephoto (such as video taken from a animated car) are plane and steady. These image stabilizers can be either visual or digital in design. visual image stabilizers regularly manipulate a prism in the lens to stabilize the image when projected on the camcorder detector. Digital image stabilizers regularly sense the camcorder petition and, taking advantage of extra rows and columns on the perimeter of the detector, shift the image an suitable number to stabilize unavoidable types of motion. Normally, the visual image stabilizers, though more expensive, are preferable since they great remove the blur component of the motion.
Lens interchangeability:
Many lower cost camcorders have non-removable objective lenses. These lenses are contract and highly integrated into the camcorder's housing, have a very wide zoom range and even macro capability. Normally, the field-of-view of the integrated zoom lens is selected to achieve the Fov range desired for most applications. However, for increased versatility, higher-end camcorders offer a detachable lens and a lens mount so that a series of lenses can be offered for a wider divergence of applications, including wider angle and more telephoto viewing. (See a list of mid-range camcorders having detachable lenses here). For non-removable lens camcorders, if wider angle or more telephoto Fov values are required, adapters are sometimes offered to change the magnification as desired. But the supervene is a allowance in visual quality. For the guard videographer, interchangeable lenses can be a great advantage if the magnification offered by fixed lens camcorders isn't sufficient for the desired application. In addition, night vision modules that are designed for detachable lens camcorders fit in the middle of the lens and camcorder and withhold all that objective lens' functions including motorized zoom, auto-iris and image stabilization.
Digital zoom:
Digital zoom is an foremost highlight for any camcorder. Because it is not possible to appreciate all the imaging detector's resolution on the camcorder's viewfinder or display panel, digital zoom enables the operator to view details on the viewfinder that would otherwise go unnoticed until digital images were later analyzed. In addition, it's beneficial to note that a detector having a larger pixel array enables the operator to achieve more digital zoom than with a camcorder having a smaller detector without the effects of pixelization.
User interface:
Any camcorder operator will confirm that accessibility to features is of some importance. Drilling down through sub-menu after sub-menu to way disposition functions is not a desirable thing to do while in the field.
Infrared mode:
Some camcorders highlight a sensitivity to near infrared light permitting the use of an infrared illuminator to brighten scenes. For a variety of reasons, these illuminators are not applicable for many guard situations. For one thing, regularly the illuminators included with the camcorders do not scheme sufficient illumination at the distances of interest. In addition, they can be detected by others with most camcorders and Ccd cameras.
Manual Gain:
For low-light situations, some camcorders offer a by hand gain mode that permits the user to manually adjust the gain in the video image, regularly increases up to +18dB. Though grainy, for guard applications, the video images are regularly a principal revision over non-gained or even auto-gained versions.
Shutter Speed:
If maintaining the suitable frame rate (for example 60Hz) is not principal because the objects under notice are not animated quickly, the frame rate and detector shutter speed can be reduced (for example to 1/3 sec) so that each of the sensor's pixels will consolidate light over a longer time that they are exposed. In darkened environments, selecting the longest suitable integration time may be sufficient to provide a usable image at dusk or dawn.
External Audio inputs:
In order to preclude the appearance of sounding like a pure optics geek, it is foremost to mention that audio ability and way to external audio inputs is foremost for the guard videographer. The built-in microphone doesn't always work well when shooting images far away or when you need something more directional to filter out ambient noise.
Viewfinder:
When performing covert surveillance, having a viewfinder on the camcorder is sometimes foremost in order to preclude the illumination from the animated Lcd panel.
Robustness:
Another serious compromise is the lack of robustness in camera hardware - the flimsy switches and controls that cause videographers stress. When you're out in the field under perhaps dangerous conditions, you don't want to be playing nearby with wee controls and Lcd panels that categorically come apart.
Price:
Of course, price is always a notice when evaluating the many many camcorders models ready today. But, what these guidelines should show is that very often, the most expensive camcorder may not be the best for a exact application. Understand what features are most beneficial for your application in notice of camcorder price range.
Conclusion
Technology improvements in Ccd and Cmos image sensors as well as the introduction of new high definition display and recording formats have resulted in the introduction of lots of separate digital camcorder models. Guidelines have been in case,granted when evaluating camcorders for use in guard applications.
For surveillance, visual image ability is of highest importance. Camcorder resolution and sensitivity are the original factors to consider, with a variety of linked factors such as image and pixel fields-of-view, the pixel size, as well as the frame rate, image stabilization, alternative lens options and lens interchangeability, integration mode, digital zoom and display resolution, user interface, video formats, recording media, by hand gain, infrared mode, video compression, external audio inputs, viewfinder, robustness, and video compression.
While these are beneficial guidelines for insight foremost camcorder specs, prior to manufacture your own camcorder buy decision, we propose that you achieve your own investigate of ready models and, based on these guidelines, agree those models that are expected to deliver the best execution and achieve your own tests under real-life situations. You may learn that other factors may be foremost to your exact application and that your final decision is a compromise of those other factors.
To View all figures and illustrations referenced in this article, Click Here
Disclaimer: We have made every attempt to provide spoton information. However, we cannot accept any responsibility for errors or inaccuracies. Should you recognize errors or need assistance, please perceive us directly. Thank you.
