RGB Spectrum SuperView 3000 Manual De Usuario
May 9, 2002
SuperView 3000 User Manual
49
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V
IDEO
L
EVELS AND
C
HROMA
K
EY
If you have the optional B
ACKGROUND
I
NPUT
connector on your SuperView
unit, then in Autosync mode you have the option of using the Chroma Key
mode. In this Autosync display option, windows selectively replace the
background computer graphics, based on the color of the graphics. The concept
of chroma key is discussed in greater detail in this chapter.
mode. In this Autosync display option, windows selectively replace the
background computer graphics, based on the color of the graphics. The concept
of chroma key is discussed in greater detail in this chapter.
The SuperView’s chroma key serves two purposes. First, it allows the
boundaries of the video window to be user-defined. You can create windows of
arbitrary shape by “painting” a window of the desired shape in the key color.
The second purpose is to overlay the video with the host computer’s graphics
and text. The host computer graphics and text are generated on the computer
screen in the same area as the window. A key color for the background of the
host computer graphics image is selected. This key color must be different from
any other color used in the computer graphics overlay. When the ChromaKey
is enabled, the window is displayed in the background of the host computer
image—i.e., the graphic overlays block out the window image, and the window
image appears where the key color is drawn.
boundaries of the video window to be user-defined. You can create windows of
arbitrary shape by “painting” a window of the desired shape in the key color.
The second purpose is to overlay the video with the host computer’s graphics
and text. The host computer graphics and text are generated on the computer
screen in the same area as the window. A key color for the background of the
host computer graphics image is selected. This key color must be different from
any other color used in the computer graphics overlay. When the ChromaKey
is enabled, the window is displayed in the background of the host computer
image—i.e., the graphic overlays block out the window image, and the window
image appears where the key color is drawn.
The key color is defined by a range of values for each of the red, green, and blue
computer signals. The selected key defines whether the host computer’s display
signal is “transparent”, i.e., if the color from the computer falls within the
specified range, the window signal is shown. For example, if a host computer
signal consists of red lines on a white background, and white is chosen as the
key color, then the resultant image on the screen is of the window overlaid by
the red lines. Considering it another way, you could say that the window “shows
through” the white area.
computer signals. The selected key defines whether the host computer’s display
signal is “transparent”, i.e., if the color from the computer falls within the
specified range, the window signal is shown. For example, if a host computer
signal consists of red lines on a white background, and white is chosen as the
key color, then the resultant image on the screen is of the window overlaid by
the red lines. Considering it another way, you could say that the window “shows
through” the white area.
The SuperView’s chroma key circuitry works by examining the values of the
host computer’s red, green, and blue signals at every point on the screen. If the
value of each signal falls in the “acceptance range” for that signal, the host
computer image is made transparent, and the windows are allowed to show
through. All three high-resolution signals (red, green, and blue) must lie
simultaneously within their respective acceptance ranges for the host computer
image to be transparent. For the windows to be made visible, the chroma key
circuitry must indicate that the host signals are within the acceptance range, at
the same region as the window location.
host computer’s red, green, and blue signals at every point on the screen. If the
value of each signal falls in the “acceptance range” for that signal, the host
computer image is made transparent, and the windows are allowed to show
through. All three high-resolution signals (red, green, and blue) must lie
simultaneously within their respective acceptance ranges for the host computer
image to be transparent. For the windows to be made visible, the chroma key
circuitry must indicate that the host signals are within the acceptance range, at
the same region as the window location.
It is not possible to key on a single color value. This is because the precision of
the digital representation of the color in the host computer’s frame buffer (or
color map) is lost when it is converted into analog form in order to drive the
color monitor. There is also variation in gain from frame buffer to frame buffer.
Even if it were possible to specify the color exactly, slight amounts of noise,
video overshoot and temperature drift would cause unreliability. Therefore, you
must specify a range of colors on which to key.
the digital representation of the color in the host computer’s frame buffer (or
color map) is lost when it is converted into analog form in order to drive the
color monitor. There is also variation in gain from frame buffer to frame buffer.
Even if it were possible to specify the color exactly, slight amounts of noise,
video overshoot and temperature drift would cause unreliability. Therefore, you
must specify a range of colors on which to key.