DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Figure 6.3 Production aperture
comprises the array S AL columns
by L A rows. Blanking intervals
lie outside the production aperture;
here, blanking intervals
are darkly shaded. The product
of S AL and L A yields the active
pixel count per frame. Sampling
rate (f S ) is the product of S TL ,
L T , and frame rate.
Figure 6.4 Clean aperture
should remain subjectively free
from artifacts arising from
filtering. The clean aperture
excludes blanking transition
samples, indicated here by black
bands outside the left and right
edges of the picture width,
defined by the count of samples
per picture width (S PW ).
The horizontal center of the picture
lies midway between the central
two luma samples, and the vertical
center of the picture lies vertically
midway between two image rows.
L T
L A
such as VITS, VITC, or closed captions. Consumer
display equipment must blank these lines, or place
them offscreen.
At the left-hand edge of picture information on a scan
line, if the video signal immediately assumes a value
greatly different from blanking, an artifact called ringing
is liable to result when that transition is processed
through an analog or digital filter. A similar circumstance
arises at the right-hand picture edge. In studio
video, the signal builds to full amplitude, or decays to
blanking level, over several transition samples ideally
forming a raised cosine shape.
See Transition samples, on page 323. Active samples encompass not only the picture, but
also the transition samples; see Figure 6.4 above.
Studio equipment should maintain the widest picture
possible within the production aperture, subject to
appropriate blanking transitions.
CHAPTER 6 RASTER SCANNING 55
S TL
S AL
S PW
PRODUCTION
APERTURE
(S AL ›‹ L A )
CLEAN
APERTURE