Appendix A StillColor
©
National Instruments Corporation A-5 NI-IMAQ User Manual
Why StillColor?
StillColor is optimized for single-frame acquisition. A StillColor
Composite acquisition acquires multiple consecutive frames. Assuming
that all frames represent the same scene of still objects, the algorithm then
uses knowledge about the composite color format to perfectly separate the
color and the luminance information.
In an NTSC video signal, two consecutive frames representing the same
object will contain the same luminance information but will have chroma
signals that are opposite in phase. By adding the two frames together, the
chroma information is cancelled, and by subtracting the two frames from
each other, the luminance signal is cancelled. The resulting separation is
now perfect, as shown in FigureA-2.
Color and luminance separation is more complex in a PAL video signal.
The IMAQ device must acquire three consecutive frames, but the same
perfect separation of the color and luminance information can be achieved
after manipulation of these images.
After separating the color and luminance signals, the StillColor algorithm
then decodes and rebuilds the color image. As shown in FigureA-2, the
result does not show any of the artifacts encountered in traditional color
decoding methods.
Composite Color Acquisition
The PCI/PXI-1408, in conjunction with NI-IMAQ, supports acquisition of
color images from an NTSC or PAL composite color video camera.
NI-IMAQ can acquire the multiple frames, decode the color information,
and rebuild the image automatically. The output image can be a simple
RGB color image or one of many image representations supported by
NI-IMAQ. See the Introduction to Color section later in this appendix for
more information on image representations.
You can connect the composite video signal to any of the four input
channels on the PCI/PXI-1408. Since StillColor is used for still scenes, you
can perform only a snap (a single-image acquisition).
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