Forums

I was wondering how the TV infers from the Master System signal that it should show a progressive image instead of an interlaced one.
I mean, the Master System is sending 50 (or 60) frames per second, just like the old analog television transmissions, but in the latter the TV understands that one frame is for odd scanlines and the other is for the even ones.
I did a quick ROM test yesterday that switches the screen contents at each frame, but of course all I get is two images flickering at 50 (or 60) Hz, so in some way the TV knows that the signal isn't an interlaced one.
How?
Thanks!

The signal timing on a normal analogue transmission delays the timing every second line to make it interleaved. The Master System doesn't. The TV just does as it is told, mostly.

I don't get it.
And I don't think the analogue transmissions had pauses between each line to 'skip' one line too...

There is a half line generated during Vsync which causes half a line shift down on the coming frame when interlacing happens. That half line causes the sweep generator to start at a slightly earlier/later moment which leads to physical shift on the screen which is the basis for interlacing.
SMS and most other game consoles do not produce half lines nor uneven amount of half lines so sweep generators always start at the same moment each frame.

This topic has taught me why nobody's made a line doubler that preserves the interlacedness of an image.

It's electronically and physically impossible! Amazing!

Author	Message
sverx Joined: 05 Sep 2013 Posts: 3814 Location: Stockholm, Sweden	interlaced Vs. progressive Posted: Fri May 04, 2018 9:20 am
	I was wondering how the TV infers from the Master System signal that it should show a progressive image instead of an interlaced one. I mean, the Master System is sending 50 (or 60) frames per second, just like the old analog television transmissions, but in the latter the TV understands that one frame is for odd scanlines and the other is for the even ones. I did a quick ROM test yesterday that switches the screen contents at each frame, but of course all I get is two images flickering at 50 (or 60) Hz, so in some way the TV knows that the signal isn't an interlaced one. How? Thanks!

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14732 Location: London	Posted: Fri May 04, 2018 1:08 pm
	The signal timing on a normal analogue transmission delays the timing every second line to make it interleaved. The Master System doesn't. The TV just does as it is told, mostly.

sverx Joined: 05 Sep 2013 Posts: 3814 Location: Stockholm, Sweden	Posted: Fri May 04, 2018 3:09 pm
	I don't get it. And I don't think the analogue transmissions had pauses between each line to 'skip' one line too...

TmEE Joined: 31 Oct 2007 Posts: 853 Location: Estonia, Rapla city	Posted: Fri May 04, 2018 5:12 pm
	There is a half line generated during Vsync which causes half a line shift down on the coming frame when interlacing happens. That half line causes the sweep generator to start at a slightly earlier/later moment which leads to physical shift on the screen which is the basis for interlacing. SMS and most other game consoles do not produce half lines nor uneven amount of half lines so sweep generators always start at the same moment each frame.

Flygon Joined: 30 Jun 2016 Posts: 196 Location: Melbourne, Australia	Posted: Sat May 05, 2018 2:10 am
	This topic has taught me why nobody's made a line doubler that preserves the interlacedness of an image. It's electronically and physically impossible! Amazing!

Forums

View topic - interlaced Vs. progressive