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by timonoko
1393 days ago
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Had to correct numbers: Super-good BW-TV was 625 x 625 x 25 = 10 Mhz. The color-carrier was 4.3 Mhz. So if you did not want to see the color-shit on your BW-TV, you had adjust the focus so that less than 625 x (4.3e6/(625 x 625 x 25)) == 275 horizontal lines were visible. TVs did not had separate adjustement for vertical focus. So all you really had was 270x270 TV. Except of course there never was 10Mhz TV-channels. It was below 8 Mhz, which was needed for full color. So there was moment of time, when we could enjoy 8Mhz black and white for a year. Almost 600 horizontal lines. And then they turned the color on and party was over. |
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The other lines are for the vertical retrace, when the video signal is blanked.
With square pixels, the B&W image would have been 576 x 768, which requires a 7.5 MHz analog video bandwidth (@ 50 Hz vertical & 15625 Hz horizontal frequencies).
Most 625-line B&W TV sets could display 576 x 768 images very well and some of the early personal computers with video outputs for TV used this format.
Nevertheless the broadcast TV signal was limited by a low-pass filter to lower horizontal resolutions, corresponding to 5 MHz analog video bandwidth in Western Europe and to 6 MHz analog video bandwidth in Eastern Europe. The reason was to provide space in the TV frequency channel for the audio signal, which used a carrier offset from the video carrier by 5.5 MHz in Western Europe and by 6.5 MHz in Eastern Europe.
So the broadcast B&W signal was worse than what the B&W TV sets could display, corresponding to 576 vertical pixels by about 510 to 620 horizontal pixels (depending on the country).