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NTSC vs. PAL. ФИНАЛ. Ставьте закладки.
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Дата: 17.03.01, @22:14
http://www.nmia.com/~roberts/vidstd 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? |
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