Phytec pciGrabber4x4, Руководство по оборудованию

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pciGrabber-4x4
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PHYTEC Messtechnik GmbH 2008 L-720e_0
6.1.2 The Videosignal and Digitization
The standard videosignal, which is processed by the Grabber, contains
625 lines, which are divided into two fields (see Figure 39). The first
field (odd field) contains lines 1 to 313, the second (even field) the
lines 314 to 625. The fields are interlaced, in order to reduce flicker of
the TV-picture. In special respect line 314 follows after line 1. Besides
various retrace- and blanking lines, the videosignal contains lines for
control and data purposes and lines for videotext information, which
restricts the actual image size to two fields of 288 lines.
Figure 39: InterlacedIimage (Example with 9 Lines)
Each field is built up within 20msec. One field provides already the
whole image, but the vertical resolution is reduced to the half. For
many applications this might be sufficient, so that after 20 msec a
digitized image is already available. In case of that the resolution in
X-direction can also be reduced, we can obtain an image without
distortion. However a reduction of the resolution in X-direction can
not speed up the digitization process, since the time base is fixed.
If the full TV-resolution is required, time has to elapse until both
fields are digitized (40 msec). Both fields follow one after another.
In order to make the interlacing of both fields possible, the last line of
the odd (the first) field, is reduced to the half. Therefore the first line
of the second field contains only the half line.