This page is a mirror of Tepples' nesdev forum mirror (URL TBD).
Last updated on Oct-18-2019 Download

Interlaced TV

Interlaced TV
by on (#193251)
I was showing someone Haunted Halloween, and explaining when Donny gets hit he blinks on and off every frame to make them look fuzzy, but then I remembered on the actual TV he doesn't blink. Due to the interlaced TV scan when he blinks on and off you only shows every other scanline consistently giving a venetian blind look(and not blinking).

I tested this today and I couldn't see it on my CRT TV but it was pretty clear on my LCD flat screen.

I took a video of this but I can't post it for a while.

Notably, you can't see it at all in an emulated setup- Computer Monitor.
Re: Interlaced TV
by on (#193252)
On a CRT, he blinks. I imagine he also blinks on an AVS, an Analogue Nt Mini, or an NES with a Hi-Def NES mod.

But on a typical consumer LCD TV displaying the composite or RF output from a stock NES Control Deck, you see combing because the LCD is treating the nonstandard 240p signal as if it were a standard 480i signal. The 240p Test Suite was developed to root out faulty deinterlacing. But TV makers appear not to care about vintage game consoles as signal sources. Some can't sync to 240p at all; others can sync only over RF or composite but not component or only over RF but not composite or component.
Re: Interlaced TV
by on (#193253)
It looks something like this...

https://video.stackexchange.com/questio ... interlaced
Re: Interlaced TV
by on (#193256)
Here's the video.

https://youtu.be/Q5LUzoqVxAk
Re: Interlaced TV
by on (#193261)
The reason is because of what Tepples has described in detail.
Re: Interlaced TV
by on (#193268)
Composite video is normally formed by 2 fields that are drawn slightly apart vertically, this is called interlaced video (480i @30Hz). However, several old consoles output video with non-standard timing that does away with the space between the fields, causing them to act like frames (240p @60Hz). This is also what causes the infamous "scanlines", which are actually the gaps where fields are never drawn in 240p video. Anyway, most newer TVs don't give a shit about the 240p signal, and decode it the same way they do 480i video, causing that annoying striped look.