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Camera Selection Guide
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Cameras supported
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Cameras
Most cameras are fine for
capturing sports motion, but some features are important when capturing
high speed objects. Manual exposure control is a critical function for
capturing blur less high speed objects.
First, a bit of background: To make video, the modern camera uses a device called a CCD (Charged Coupled Device). This thing looks like a chip, and has thousands of little buckets that collect light. To take a picture the camera opens the shutter letting light in for a controlled amount of time and then reads the amount of light in each bucket. Frame Rate, is the number of pictures or frames the camera takes per second (FPS). Exposure, is the amount of time the camera shutter is open.
A regular TV works at 25FPS PAL, 29.97FPS NTSC, this why every video camera uses that magic 30FPS. To analyze athletic you need between 15 to 30FPS. Software companies advertise 50-60 FPS, but this higher frame rate is teased out of DV and TV cards by cutting the video resolution in half to get 2 frames from one. Higher frame rates are possible but with industrial video systems (Bottle line inspection) but are expensive ($15,000).
Blurring is the biggest issue with video and athletic movement. Blur, is caused by the subject moving while the camera shutter is open. Blur, is reduced by limiting the exposure time. Although the camera is capturing frames at 25-30 frames per second, the camera shutter may only be open 1/1000th of a second per frame. If a bat/ball is moving at 100mph with a 1/1000th of a second exposure, that bat/ball can only move 0.18 inches (45 mm). Exposure around 1/500th results in good video.
With every advantage, there is a disadvantage. Reduced exposure limits the amount light going into the camera, reducing the brightness of the picture. You can reduce the exposure to the limit of the camera in the bright sun, but when indoor, getting enough light is difficult so you will have balance blur-less pictures for bright pictures.
Now that the theory of blur free video is outlined, what camera will you use? Manual Exposure control is the key. Professional TV cameras have this feature, but they are expensive. The high-volume low cost consumer cameras are a mixed bag. Many consumer cameras only have “Sports Mode” for high-speed action shots.
When in “Sports Mode” the computer inside the camera looks at the background
of your picture using background movement to automatically adjust
the exposure. When the background moves the exposure time will reduce,
otherwise, the camera optimizes for picture brightness. In cricket batting, golf swings
and tennis serves, the background never moves, even the athlete's body
should also not move that much. The result is the camera thinks nothing is
moving so it makes the exposure time longer, resulting in
blur.
USB
USB and Firewire (IEEE1394) are
serial bus technologies, the way the camera and computer communicate.
USB is the standard for a type of low cost camera called WebCams. Webcams are basically a small video camera and analog to digital video convertor with a USB interface. These devices do not provide zoom or tape storage for video. The resolution of the video from these cameras is limited by the USB interface. 320x240 pixels is the maximum you can transfer over USB at 30 frames per second.
The advantage of these Webcams is that they are cheap simple and avalable everywhere. Also they get they power from the computer so there is no extra batteries to manage.
Recently USB has been upgraded. USB 2.0 now provides bandwidth up to 460Mbs up from 6Mbs of USB1.1. A few new Webcams using USB 2.0 are avaliable on the market with resolutions of 640x480 at 30 frames per second.
Firewire
Firewire
or IEEE1394 is a serial technology developed
specially for video transfer. Any digital video camera will
support this standard. Digital video cameras will provide resolutions of
720x588 pixels at 25 frames per second 720x480 at 30 FPS. The reason
for this high resolution is the 600Mbs provided by firewire.
Firewire or Digital video (DV) cameras are typically full featured cameras combining zoom, video effects, tape storage, video playback and many other features into a small package.
DV cameras are more expensive then regular video cameras or Webcams but provide the best results.
Composite (Regular Analog Camcorder)
These devices have been around
for years, camcorders that store video to tape and provide various
functions with the video. The problem is how to get analog video into a
digital computer. To do this there are two options.
First option is a TV card. These cards are low cost and provide good quality results, and in many cases come with your monitor card (ATI all-in-wonder). The problem is these cards are PCI and need to plugged on the inside of your computer. The second option is to use a Video to USB converter.
These devices are simple to use and are low cost. The trade-off of these devices is that the quality of the video is similar to a Webcam.
