DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Progressive
Interlaced
Image row
0
1
2
3
DYNAMIC
tn (1/60 s) tn+1 (1/60 s)
Image row
0
1
2
1
2
Line number
(first field)
0
1
2
3
0
1
2
STATIC
Figure 6.8 Progressive and interlaced scanning are compared. The top left sketch depicts an
image of 4×3 pixels transmitted during an interval of 1 ⁄60 s. The top center sketch shows image
data from the same 12 locations transmitted in the following 1 ⁄60 s interval. The top right sketch
shows the spatial arrangement of the 4×3 image, totalling 12 pixels; the data rate is 12 pixels per
1 ⁄60 s. At the bottom left, 12 pixels comprising image rows 0 and 2 of a 6×4 image array are transmitted
in 1 ⁄60 s. At the bottom center, the 12 pixels of image rows 1 and 3 are transmitted in the
following 1 ⁄60 s interval. At the bottom right, the spatial arrangement of the 6×4 image is shown:
The 24 pixel image is transmitted in 1 ⁄30 s. Interlaced scanning has the same data rate as progressive,
but at first glance has twice the number of pixels, and potentially twice the resolution.
Notation Pixel array
VGA 640×480
SVGA 800×600
XGA 1024×768
SXGA 1280×1024
UXGA 1600×1200
QXGA 2048×1365
Table 6.2 Scanning in
computing has no standardized
notation, but these
notations are widely used.
considered worthwhile. The improvement comes at the
expense of introducing some aliasing and some vertical
motion artifacts. Also, interlace makes it difficult to
process motion sequences, as I will explain on page 61.
Scanning notation
In computing, display format may be denoted by a pair
of numbers: the count of pixels across the width of the
image, and the number of picture lines. Alternatively,
display format may be denoted symbolically – VGA,
SVGA, XGA, etc., as in Table 6.2. Square sampling is
implicit. This notation does not indicate refresh rate.
Traditionally, video scanning was denoted by the total
number of lines per frame (picture lines plus sync and
vertical blanking overhead), a slash, and the field rate in
CHAPTER 6 RASTER SCANNING 59
3
4
Line number
(second field)