NTSC: The frame rate is chosen to be very close to the
frequency of the power system. In the US, we use 60Hz power, so
the NTSC frame rate is 59.94 Hz. The reason you want the same
rate as the power frequency is to minimize interference. The
line rate is 525 lines. The line frequency, frame frequency and
color carrier frequency are all related to each other, and are
actually locked to each other. All the needed timing signals
can be divided from one master clock signal. The color carrier
for NTSC is 3.58 MHz, for short. There are many more digits.
The color information, consisting of Red, Green and Blue, are
all present at the color TV camera. The black/white signal is
made by mixing the three colors, 0.30Red, 0.59Green and
0.11Blue. The two color signals needed to make a full color
picture is R-Y (red minus black/white), and B-Y (blue minus
black/white). If you transmit the Y (black/white) signal and
the two combination colors, R-Y and B-Y, you can extract the
green color using simple adding and subtracting. Green = Y-R-B
For NTSC, the two color signals are modulated on the color
carrier using quadrature AM modulation. It's possible to keep
the two R-Y and B-Y signals on one carrier. To extract the two
signals at the receive end, you must also transmit a color
reference signal, called the color burst. This short burst of
unmodulated color carrier is placed right after every horizontal
sync pulse (about 15000 times per second). The color burst is
used to lock the color demodulator in the TV set so the correct
R-Y and B-Y signal can be demodulated. Now, the black/white
signal and the two color signals can be combined to make Red,
Green, and Blue, all the color information needed to make a full
color picture on your TV set.
PAL:
PAL is fairly close to NTSC. Since the power frequency is
50Hz, the frame rate is also 50 Hz. The line rate is 625 lines.
However, the Europeans didn't like the color change that can
occur if there is a phase change in the transmission of the
signal. So on NTSC TV sets there is a HUE or TINT control to
correct for any phase change of the color burst/color signal.
One way of making an "automatic" hue control is to transmit the
R-Y signal alternately with a phase shift of 90 degrees. In
every other line the R-Y signal is transmitted inverted. Since
our eyes are less sensitive to color compared to black/white,
the resolution needed for color is less. As you know, the
black/white resolution is about 5 MHz, however the color
information transmitted on the color carrier is about 1.4 MHz
wide. The frequency of the carrier is 4.43 MHz. So, in PAL,
they assume the vertical resolution can be cut in half without
"affecting" color resolution. By combining two horizontal
lines, using a delay line in the TV set, two lines can be
combined and any phase error can be cancelled. Severe phase
changes in the transmission of a PAL signal will show up as weak
colors, but correct colors. In NTSC it will show up as full
color saturation, but the wrong colors! It's also a fact that
our eyes are much more sesitive to color hue changes than to
color saturation changes. So, you will not see green faces in
PAL, but you might see weaker (!!!!!!!!!!) colors.
Еще
http://www.ee.surrey.ac.uk/Contrib/WorldTV/compare.html
Итог (с) Никки
Если в двух словах, то в PAL интенсивность цветов ослабляется,
но зато цвета всегда правильные (кроме якростной составляющей).
В NTSC напротив - интенсивность точек всегда правильная, но
цвета - нет.
Так что лица с брильянтовым оттенком - удел NTSC. А блеклость, но
без зелени - PAL.
http://www.dvdspecial.ru/cgi-bin/ultiweb.cgi?mode=show_message&id=11697
Все. Надеюсь, все точки над i расставлены. Фокстри, ты прочел?
NTSC vs. PAL. ФИНАЛ. Ставьте закладки. -- BFG -- 17.03.01@22:14 (Чит.: 165)