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Do I understand * blanking correctly?

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Daniel Sleeth
Do I understand * blanking correctly?
on Jan 16, 2015 at 2:28:47 pm

I am trying to get my head around horizontal, vertical and digital blanking intervals, but I have nobody to confirm whether what I understand from it is accurate...

Let's assume I have an analogue television that is 20 pixels by 10 pixels (to make things simple). The image starts at the top left pixel (row 1, pixel 1) and pixels come on one-by-one until the end of that row (row 1, pixel 20) at which point there is horizontal blanking until the beam moves back along and down to the start of the next row (row 2, pixel 1). The process repeats with horizontal blanking taking place at the end of each row.

When the beam gets to the last pixel in the image (row 10, pixel 20) there is vertical blanking until it returns to (row 1, pixel 1).

a) is what I've explained correct so far?
b) is there vertical blanking as well as horizontal blanking at the end of the very last pixel, as the beam is travelling all the way across the image?
c) does vertical and horizontal blanking only take place on analogue TVs, as I thought pixels on digital televisions could be individually targeted using their coordinates (there is no beam scrolling across the screen)

Thanks for any help you can give. My brain hurts a little!

Dan


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Tom Matthies
Re: Do I understand * blanking correctly?
on Jan 16, 2015 at 7:44:04 pm

It's a little dense but this article explains a lot.
Your explanation is most correct. In analog (NTSC) video, once the first line is scanned, the next line to be scanned is actually line 3 (not line 2). This goes on scanning every odd line until the bottom of the screen. At this point, back at the top of the picture, the even lines are displayed and interlaces with the odd lines. This is where the concept of interlaces TV is formed. All of the odd lines are displayed and in the next 1/60th of a second the even lines are displayed forming a full raster in 1/3oth of a second-for NTSC. PAL is a bit different but similar. ATSC TV is different. Here the blanking intervals are needed mostly for proper timing of the signals and not necessarily for the blanking of the electron beam within the receiver. It's important in the timing of the transmission signals and in the decoder of an ATSC receiver. Same timing but different reasons.

Not my monkeys. Not my circus.


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Tom Matthies
Re: Do I understand * blanking correctly?
on Jan 16, 2015 at 7:54:01 pm

I suppose it would help to add the link to the article.

http://en.wikipedia.org/wiki/NTSC

For ATSC TV:
http://www.atsc.org/cms/index.php/standards/standards

For NTSC analog:
http://antiqueradio.org/art/NTSC%20Signal%20Specifications.pdf

Not my monkeys. Not my circus.


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Daniel Sleeth
Re: Do I understand * blanking correctly?
on Jan 26, 2015 at 9:23:37 am

Thanks a lot for your reply! I have read the links and they have been helpful - though I am still slightly confused! I have been tasked with making some animations to explain these functions. Blind leading the blind...

Thanks again!! I'll post the videos here when I am done lol


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