Confusion about interlacing

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twosixonetwo
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Confusion about interlacing

Post by twosixonetwo » Tue Feb 25, 2014 3:51 pm

Hey,

I have been frequently told that the Mega Drive/Genesis is always outputing interlaced video. I was quite sure, that this meant that only every other line was being output every other frame. This seemed unlikely since I remembered some games having effects which were based on turning sprites on and off with each frame, and if the Mega Drive only outputs every other line, you would see the lines in the sprite, instead of the illusion of the sprite being transparent.
I even wrote a tiny test with the help of SGDK, which flickers to colors in a horizontal stripe pattern. When run on a real Mega Drive (and crt) both colors show in heavy flicker, just like the Mega Drive outputs progressive scan.
So my question is: Did I misunderstand the concept of interlacing, or does the Mega Drive output 224p video?

Chilly Willy
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Post by Chilly Willy » Tue Feb 25, 2014 4:07 pm

Most games output 240p. The MD is CAPABLE of interlaced video, but very few games actually use it.

r57shell
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Post by r57shell » Tue Feb 25, 2014 4:37 pm

As I told you, Chilly Willy give the image right from start :D

But I'll give link where we discuss a much.
viewtopic.php?t=1685
Image

twosixonetwo
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Post by twosixonetwo » Tue Feb 25, 2014 6:05 pm

Thanks! I knew that there was an interlaced mode, I just heard some people saying that the Mega Drive wasn't capable of any progressive scan at all. Seems like they were wrong :D

Chilly Willy
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Post by Chilly Willy » Wed Feb 26, 2014 6:52 pm

twosixonetwo wrote:Thanks! I knew that there was an interlaced mode, I just heard some people saying that the Mega Drive wasn't capable of any progressive scan at all. Seems like they were wrong :D
They probably mean HD TV progressive modes, like 720x480p, or 1280x720p. The progressive mode that virtually all old consoles and home computers use (240p) is not an accepted progressive mode, just a mode that works on most old TVs. Newer LCD TVs often don't support it, making the picture from an old console look like crap because they're trying to deinterlace a progressive signal.

tomaitheous
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Post by tomaitheous » Thu Feb 27, 2014 1:01 pm

Chilly Willy wrote:
twosixonetwo wrote:Thanks! I knew that there was an interlaced mode, I just heard some people saying that the Mega Drive wasn't capable of any progressive scan at all. Seems like they were wrong :D
They probably mean HD TV progressive modes, like 720x480p, or 1280x720p. The progressive mode that virtually all old consoles and home computers use (240p) is not an accepted progressive mode, just a mode that works on most old TVs. Newer LCD TVs often don't support it, making the picture from an old console look like crap because they're trying to deinterlace a progressive signal.
I remember, from days of old, when working at a public access station - that you were not allowed to broadcast 240p. 480i only. That was for any station across the US. You would have to line double the 240p image to 480i30. Matter of fact, I never find official documentation supporting the 240p format. I think it was more of a hack that just worked (at least at first). There were some TVs that didn't like it BITD, I remember having this problem with the SNES on a friends TV from the 80's. TG and Genesis worked fine on it, though.

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