STH-DCAM U
SER
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S
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ANUAL
2001 V
IDERE
D
ESIGN
6 User
Controls
The CCD imagers are fully controllable via the IEEE 1394 interface. User
programs may input color images, set video digitization parameters
(exposure, gain, red and blue balance), and frame size. All of these
parameters can be set with the included capture application, or with the SRI
Small Vision System. They are also accessible to user programs through
the capture API (Section 8).
User controls for frame size and sampling modes are on the main capture
window dialog. Video digitization and Subwindowing controls are
accessed through a dialog invoked with the
Video…
menu item. Figure 6-1
shows the dialog.
6.1 Color
Color information from the STH-DCAM digital head is input as raw
colorized pixels, and converted by the interface library into two
monochrome channels and one RGB color channel. The color channel
corresponds to the left image, which is the reference image for stereo. The
color image can be de-warped, just like the monochrome image, to take into
account lens distortion (see the Small Vision System User’s Manual).
Color information from the camera is input only if the
Color
buttons are
pressed on the main window (Figure 2-1). Color/monochrome can only be
changed while the STH-DCAM is not outputting images.
Because the typical color camera uses a colorizing filter on top of its pixels,
the color information is sampled at a lower resolution than a similar non-
colorized camera samples monochrome information. In general, a color
camera has about ¼ the spatial resolution of a similar monochrome camera.
To compensate for the reduced resolution, use binning (Section 6.3) to
increase the fidelity of the image. For example, if you need a 320x240
frame size, use 640x480 and binning x2.
The relative amounts of the three colors, red/green/blue, affects the
appearance of the color image. The STH-DCAM CCD imagers have
attached processors that automatically balance the offsets among these
colors, to produce an image that is overall neutral (called
white balance
).
Alternatively, the application program can control the color balance
manually. Manual balance is useful in many machine vision applications,
because automatic white balance continuously changes the relative amount
of color in the image.
Figure 6-1 Video Parameters dialog.
The manual gain on red and blue pixels is adjusted using the
Red
and
Blue
controls on the
Video Parameters
dialog. For a particular lighting source,
try adjusting the gains until a white area in the scene looks white, without
any color bias.
6.2 Video Digitization Parameters
The CCD imagers have electronic exposure and gain controls to
compensate for varying lighting conditions. The exposure can vary from a
maximum of a full frame time to a minimum of one line time. Gain is an
additional amplification of the video signal, for low-light situations. It is
settable from 0 to 18 dB.
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