CCD cameras
Computer vision on reactive robots ismost often froma video camera, whichuses CCD (charged couple device) technology to detect visible light. A video
camera, such as a camcorder, is arranged so that light falls on an array of
closely spaced metal-oxide semiconductor (MOS) capacitors. Interestingly,
the MOS capacitors are rectangular, not square, so there is some distortion
in creating the image. The capacitors form a shift register, and output is
either a line at a time (“line transfer”) or the whole array at one time (“frame
transfer").
The output of most consumer video signals is analog, and must be digitized
for use by a computer. Consumer digital cameras post an analog signal,
but the update rate is too slow at this time for real-time reactive robot control.
The A/D conversion process takes longer than the CCD array can sense
light, so the camera device can either have many frame buffers, which create
a pipeline of images (but is expensive), or have a low frame rate.
A framegrabber is FRAMEGRABBER a card which fits inside a computer, accepts analog camera
signals and outputs the digitized results. The card has a software driver
which allows the robot software to communicate with the board. Framegrabbers
can produce a grayscale or a color digital image. In the early part of
the 1990’s, color-capable framegrabbers were prohibitively expensive, costing
around $3,000 USD. Now color framegrabbers can be purchased from
$300 to $500 USD, and TV tuners which can capture a single frame are available
for $50 USD.
