DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Flicker is sometimes redundantly
called large-area flicker. Take care to
distinguish flicker, described here,
from twitter, to be described on
page 57. See Fukuda, Tadahiko,
“Some Characteristics of Peripheral
Vision,” NHK Tech. Monograph No. 36
(Tokyo: NHK Science and Technical
Research Laboratories, Jan. 1987).
Raster scanning 6
I introduced the pixel array on page 6. In video, the
samples of the pixel array are sequenced uniformly in
time to form scan lines, which are in turn sequenced in
time throughout each frame interval. This chapter
outlines the basics of this process of raster scanning. In
Chapter 11, Introduction to component SDTV, on
page 95, I will present details on scanning in conventional
“525-line” and “625-line” video. In Introduction
to composite NTSC and PAL, on page 103, I will introduce
the color coding used in these systems. In
Chapter 13, Introduction to HDTV, on page 111, I will
introduce scanning in high-definition television.
Flicker, refresh rate, and frame rate
A sequence of still pictures, captured and displayed at
a sufficiently high rate, can create the illusion of motion.
Many displays for moving images emit light for just
a fraction of the frame time: The display is black for
a certain duty cycle. If the flash rate – or refresh rate – is
too low, flicker is perceived. The flicker sensitivity of
vision is dependent upon the viewing environment: The
brighter the environment, and the larger the angle
subtended by the picture, the higher the flash rate must
be to avoid flicker. Because picture angle influences
flicker, flicker depends upon viewing distance.
The brightness of the reproduced image itself influences
the flicker threshold to some extent, so the
brighter the image, the higher the refresh rate must be.
In a totally dark environment, such as the cinema,
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