DVD Demystified

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Figure 12.6
Video safe areas
Chapter 12
and reappear 60 times a second. This interlaced twitter effect (also called
flicker) can be especially bad with computer-generated graphics. In addition
to interlace artifacts, chroma crawl and color crosstalk from composite
video signals make thin lines or sharp color transitions problematic,
despite their orientation.
To reduce these effects, use the antialiasing and feathering features of
your graphics software whenever possible. Make sure that all horizontal
lines are at least two pixels thick. To be even more careful, keep the thickness
of horizontal lines at multiples of two pixels. 7 Use gradual color transitions
instead of sharp contrasts between dark and light colors. To adapt
existing graphics, or as a final pass before encoding, apply a blur filter to the
entire image or to offending areas. For example, a Gaussian blur of 0.5 to 1
has little visual effect but helps to reduce video artifacts. Also, because blurring
reduces high-frequency detail, the MPEG compression will be more
efficient, possibly resulting in higher quality.
7 This advice only applies when you are working at native NTSC video resolution of 480 lines. If
you create graphics at higher resolutions, the number of pixels will change when the graphic is
scaled down. This doesn’t apply to 625-line (PAL) video, since it’s generally scaled horizontally,
not vertically.