Appendix B
StillColor
©
National Instruments Corporation
B-5
PCI/PXI-1408 and NI-IMAQ for Win95/NT
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 Figure B-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
Figure B-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).