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In Figure 8-4, each pixel is shown to have two halves - a Clocked Well (CW) and a Virtual Well
(VW). The transfer of charge (that takes place in the vertical blanking interval) uses a slightly
different mechanism for the two fields. In the odd field, the first transfer pulse clocks the charge
from each CW to the adjacent (lower) VW. In the even field, the first transfer pulse clocks the
charge from each VW to the adjacent (lower) CW. As shown in the diagram, this causes the
effective pixel area and centroid of each pixel to be shifted by half of the pixel height from the
odd field to the even field.
By the above process, the charge collection area represented by each pixel is electronically
shifted vertically from field to field by half of the pixel height. This is analogous to the process of
"dithering" the pixel matrix vertically at 60 Hz.
Using the two displaced imaging areas, two distinct video fields are created. The resulting
interlaced video image may be viewed on a monitor as an image with a higher vertical
resolution.
In Image Processing applications, the frame storage memory must be designed in a way that
allows the writing of odd-numbered rows during the ODD field and the even-numbered rows
during the EVEN field. The FIELD INDEX signal (HIGH during the EVEN field) is provided to
simplify the addressing of the frame storage memory.
8.4.7 Can the pseudo-interlaced operation be disabled ?
In applications where a vertical resolution of 242 is sufficient, the interlace operation can be
disabled. With the interlace disabled, both fields represent the same physical pixel matrix; the
charges, however, are derived from integration periods that are 1/60th of a second (one field
period or 16.66 mS) apart.
To disable interlace, the integration level potentiometer on the video board should be adjusted.
On more recent versions of the video board, a switch is provided for this purpose.
Contact DVC before making such an adjustment !
8.4.8 What is anti-blooming ?
Blooming: is defined as the phenomenon in which a bright spot of light in the field of view of a
video camera appears to be larger in size. Needless to say, this is an unwanted artifact in the
image.
Anti-blooming: is the method by which the effect of blooming is minimized (or eliminated).
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