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Re: а RGB лучше
Автор: Pin
Дата: 18.03.01, @00:30
`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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