DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

For a modest improvement over
2-tap averaging, use 4 taps with
coefficients [ 1 ⁄ 16 , 7 ⁄ 16 , 7 ⁄ 16 , 1 ⁄ 16 ].
VERTICAL
TEMPORAL
Figure 37.6 V·T development
Figure 37.7 Storage system
to implement deinterlacing
can be implemented
with two fields of memory.
This drawing suggests 525
lines of storage, but it
suffices to store just the
active lines.
lution. Nonetheless, the method performs well for VHSgrade
images, which lack resolution in any case. Rather
than simply averaging two lines, improved performance
can be attained by using longer FIR filters with suitable
tap weights; see Filtering and sampling, on page 141.
Vertical-temporal domain
Interlace-to-progressive conversion can be considered
in the vertical-temporal (V·T) domain. Figure 37.6 in the
margin sketches the Interlaced capture fields of
Figure 37.2, in a 3-dimensional view. Viewed from the
“side,” along the axis of the scan lines, the verticaltemporal
domain is projected. The temporal samples
are at discrete times corresponding to the field instants;
the vertical samples are at discrete intervals of space
determined by the scan-line pitch. The four open disks
represent samples of original picture information that
are available at a certain field instant and line number.
A calculation on these samples can synthesize the
missing sample value at the center of the pattern. In the
diagrams to follow, the reconstructed sample will be
drawn as a filled disk. (A similar calculation is
performed for every sample along the scan line at the
given vertical and temporal coordinate: For Rec. 601
digital video, the calculation is performed 720 times per
scan line.)
Figure 37.7 shows the block diagram of a storage
system that can be used to implement interlace-toprogressive
conversion.
CHAPTER 37 DEINTERLACING 439