|Per Hour||206.10 MB|
|Per Day||2.47 GB|
|Per Period||123.66 GB|
|Per Hour||10.31 GB|
|Per Day||123.66 GB|
|Per Period||6.18 TB|
Some object details are visible. For humans this would include visibility of individual arms and legs, and potentially clothing or weapons.
The object can be classified. Viewers should be able to discern the type of object (such as human) from other similar-sized objects (such as deer).
The object is visible. At a minimum it will appear as a dot on the screen.
Lens Selection Guide
The focal length of the lens is measured in mm and directly relates to the angle of view that will be achieved. Short focal lengths provide wide angles of view and long focal lengths become telephoto, with narrow angles of view. A "normal" angle of view is similar to what we see with our own eye, and has a relative focal length equal to the pick up device. Our online lens calculator is a simple to use device for estimating focal length, object dimension, and angles of view.
The size of the camera's imaging device (CCD) also affects the angle of view, with the smaller devices creating narrower angles of view when used on the same lens. The format of the lens, however, is irrelevant to the angle of view, it merely needs to project an image which will cover the device, i.e.: the same format of the camera or larger. This also means that 1/3" cameras can utilize the entire range of lenses from 1/3" to 1", with a 1/3" 8mm lens giving the same angle as a 2/3" 8mm lens. The latter combination also provides increased resolution and picture quality as only the center of the lens is being utilized, where the optics can be ground more accurately.
The lens usually has two measurements of F stop or aperture, the maximum aperture (minimum F stop) when the lens is fully open, and the minimum aperture (maximum F stop) just before the lens completely closes. The F stop has a number of effects upon the final image. A low minimum F stop will mean the lens can pass more light in dark conditions, allowing the camera to produce a better image at night. A maximum F stop may be necessary where there is a very high level of light or reflection, as this will prevent the camera from "whiting out", and help maintain a constant video level. All auto iris lenses are supplied with Neutral Density spot filters to increase the maximum F stop. The F stop also directly affects the depth of field.
DEPTH OF FIELD
The depth of field refers to the area within the field of view which is in focus. A large depth of field means that a large percentage of the field of view is in focus, from objects close to the lens often to infinity. A shallow depth of field has only a small section of the field of view in focus. The depth of field is influenced by several factors. A wide angle lens generally has a larger depth of field than a telephoto lens, and a higher F stop setting typically has a larger depth of field than a lower setting. With auto iris lenses, the automatic adjustment of the aperture also means constant variation of depth of field. The small depth of field is most apparent at night when the lens is fully open and the depth of field is at its minimum. Objects that were in focus during the day may become out of focus at night.
AUTO or MANUAL IRIS
Generally we tend to use auto iris lenses externally where there are variations in the lighting levels. Manual iris lenses are used normally for internal applications where the light level remains constant. However, with the introduction of electronic iris cameras it is now possible to use manual iris lenses in varying light conditions and the camera should electronically compensate. There are several considerations to this option though: the setting of the F stop becomes critical; if the iris is opened fully to allow the camera to work at night, the depth of field will be very small and it may be more difficult to achieve sharp focus even during the day. The camera can maintain normal video levels, but it cannot affect the depth of field. If the iris is closed to increase the depth of field, the low light performance of the camera will be reduced.
VIDEO DRIVE or DIRECT DRIVE
With auto iris lenses it is necessary to control the operation of the iris to maintain perfect picture levels. Video driven lenses contain amplifier circuitry to convert the video signal from the camera into iris motor control. With direct drive lenses, the camera must contain the amplifier circuitry, and the lens now only contains the galvanometric iris motor making it less expensive. The deciding factor depends on the auto iris output of the camera. Most now have both types.
Please select a FPS setting to preview videos below
One thing you need to be careful about when analyzing specifications of a DVR with respect to "frames", "fields" or "images" per second capabilities is what are they talking about:
- The total number of frames/images per second for the entire card to be spread across all cameras (cumulative total)
- The total number of frames for each individual channel
- The maximum frame capacity of the hardware not taking into account software switching, simultaneous functions, etc. (rated hardware capacity)
- Display speed
- Recording speed
- "I" frame "B" frame or "P" frame calculation
- Is it really images or are they even calculating frames which also provides misleading figures
There are an infinite number of ways of presenting these numbers, many of which are misleading. Sounds like financial reporting on Wall Street! Remember that 30 frames per second is real-time / real motion video, but that is for a single video stream. So if you want to record 4 cameras simultaneously, all in real-time/real motion video, you need 120 frames per second and its full unshared resources. To drill down even further you have to question at what resolution is the real time image being displayed. Many systems can only record real-time if the resolution is lowered.
The frame rate issue is a very tricky one. The fact is the speeds that manufacturers quote are usually the "maximum" obtainable, meaning under ideal conditions, and does not take into account anything else the PC, software, or video card might be doing. In other words it's like the MPG sticker on your new car - good luck trying to get that mileage; maybe downhill in neutral with a strong tailwind.
To add further to the confusion are some manufacturer quotes "IPS" (image per second). An "FPS" (frames per second) why do they do this-because 2IPS=1FPS. Therefore, it takes 60IPS to equal 30FPS or a single real-time image. It becomes more convoluted because in "images" per second there are "initial" frames and subsequent frames which refresh only changed portions of the image. Confused yet! Well make sure they are talking "Frames" per second and not "Fields" per second, as similar to IPS there are two fields to each frame.
We keep calling them "capture" cards because they are "capturing" and recording video, but what plays back and displays the video on the screen? The answer is the capture card. Even though it is "capturing" (encoding) the video, it also handles the video display on the card (decoding).
Some other math we need to learn. If we already know about the alleged maximum recording frame/image rate of the board, what about the video display? Sorry, but yes we have to add that into the equation.
So, now that you are displaying and capturing at the same time, the performance may proportionately diminish, as they may be sharing the same components to accomplish different tasks. One function must wait for the other or both perform at a reduced rate. To counteract this problem some companies use a separate video display card (decoder), which generates real-time video on all channels all the time. A live video display card usually has separate chips for each group of channel of video displayed. Each chip is capable of generating a true 30 frames per second image per channel across multiple channels. It is a live feed from the board directly to the monitor and each channel transmits its own video, without the need for the software to compress the video signal. This should not be confused with the VGA video card, which is entirely different. Today, there are also several newer technologies that are capable of providing real-time images and multiple channels without the need for a live display card but they come at a price.
Let's jump back now to, how the heck does this capture card work. After all, raw video uses a tremendous amount of data and we are talking about transmitting as many as 64 simultaneous camera images from a single machine. Making practical to send, receive and store huge amounts of data requires video compression before it can be transmitted.
There are 2 types of physical compression; hardware and software. It is actually a case of compression and decompression. Compress it to travel down the network and decompress to transmit when it comes out the other side, so the name "Codec." When you use hardware compression there is no loss of efficiencies, as all the work is being done on the board by the hardware components. That is of course if you have all the right components.
Software compression utilizes software to perform specific operations. When performed simultaneously in conjunction with other functions it has a taxing effect on overall system performance. The software uses the available hardware resources such as processor and memory to complete its task.