TV safe area

[Shiru]

It's not technically a legal NTSC signal (out of all the NTSC books and docs I have anyway), but almost all (99.9999999%) TVs support it.

One of most popular DIY ZX Spectrum clones in Russia had so simplified video system so it had whole 320 lines instead of 312.5 per frame (so framerate was 48.82Hz). And that worked with all TV's and monitors of that time (1990s), that clone even was demoscene standart. Only nowadays we got problems with TV-tuners, video projectors etc - they not accept so non-standart sync.

[tomaitheous]

It's not technically a legal NTSC signal (out of all the NTSC books and docs I have anyway), but almost all (99.9999999%) TVs support it.

One of most popular DIY ZX Spectrum clones in Russia had so simplified video system so it had whole 320 lines instead of 312.5 per frame (so framerate was 48.82Hz). And that worked with all TV's and monitors of that time (1990s), that clone even was demoscene standart. Only nowadays we got problems with TV-tuners, video projectors etc - they not accept so non-standart sync.

Wow... that far off and it still worked? Heh- that's pretty cool. On the PC Engine, you can select between two modes - 262 or 263 scanline. If you switch between then on every frame, then the TV will generate a 480i type image. Of course this doesn't work on newer LCD and HDTVs. It works on my capture card though. The VDC(video processor that handles tiles and sprites like the VDP) can generate up to a 512 progressive image (or 480i if you needed), but the video encoder chip doesn't support it.

Evildragon: Those could be "equalization pulses" on the first few scanlines. Really-really old NTSC sets needed them (I forget what for...). It would make sense that the Atari system would generate them considering the '70's people probably still had old sets that required them. I think the SNES omits these and that why some TV's pre 1985 will "geek out" when using said system(and other systems too).

[evildragon]

this is that pulse thing.

http://blackevilweredragon.spymac.com/pulse.mov

(QT, QT Alternative, or VLC can play that vid.. no audio track, H.264 video track)

[Eke]

You're thinking about it wrong: there are two fields that make up each frame, an even and an odd field. We say the field rate is 60Hz because every 60th of a second, ONE of the two fields is displayed. Since a single field is not the entire frame, the field rate is not the frame rate. It takes two fields to make a complete frame, so it takes two 60ths of a second to show a frame. So the frame rate is 60Hz/2, or 30Hz.

Yes, each field is only shown 30 times a second, but there are two fields shown in that time. The field rate refers to ALL fields, not one specific field.

You're forgetting about the half line on the last scanline. For consoles of the 8 and 16 bit era ( and other consoles too), 240p is achieved by omitting the half scanline. So you output 262 or 263 scanlines, not 262.5. This causes the TV display to place all *fields* in the exact same place and this is why you see the scanline *gap* that emulaters try to simulate - called "scanlines". Thus fields become frames.

It's not technically a legal NTSC signal (out of all the NTSC books and docs I have anyway), but almost all (99.9999999%) TVs support it.

so would this mean that, in interlaced mode, the genesis vdp ouputs alternatively 262 and 263 lines (313 and 312 when PAL is set) ?

I guess a quick way to know would be to observe /CSYNC or better, two consecutive /VYSNC periods and /HSYNC period in two consecutive frame (to see if the line frequency is changing or not, meaning the framerate is not constant), running a game that use one of the interlaced modes

[tomaitheous]

You're thinking about it wrong: there are two fields that make up each frame, an even and an odd field. We say the field rate is 60Hz because every 60th of a second, ONE of the two fields is displayed. Since a single field is not the entire frame, the field rate is not the frame rate. It takes two fields to make a complete frame, so it takes two 60ths of a second to show a frame. So the frame rate is 60Hz/2, or 30Hz.

Yes, each field is only shown 30 times a second, but there are two fields shown in that time. The field rate refers to ALL fields, not one specific field.

You're forgetting about the half line on the last scanline. For consoles of the 8 and 16 bit era ( and other consoles too), 240p is achieved by omitting the half scanline. So you output 262 or 263 scanlines, not 262.5. This causes the TV display to place all *fields* in the exact same place and this is why you see the scanline *gap* that emulaters try to simulate - called "scanlines". Thus fields become frames.

It's not technically a legal NTSC signal (out of all the NTSC books and docs I have anyway), but almost all (99.9999999%) TVs support it.

so would this mean that, in interlaced mode, the genesis vdp ouputs alternatively 262 and 263 lines (313 and 312 when PAL is set) ?

I guess a quick way to know would be to observe /CSYNC or better, two consecutive /VYSNC periods and /HSYNC period in two consecutive frame (to see if the line frequency is changing or not, meaning the framerate is not constant), running a game that use one of the interlaced modes

When the Genesis is in interlaced mode, it outputs 262.5 (and half line for PAL too I think, but I'm not 100% sure on that) for every 59.94hz. Charles confirmed this a few months back. The 262/263 alternative thing is a hack Charles MacDonald did for the PC Engine. The Genesis outputs true interlaced mode - though he told he found some weird multiple half lines near end of the frame generation from the Genesis in interlaced mode, but they added to the correct amount of 262.5.

Evildragon: You should see if you can run it through a TV capture card. If it shows up on there, then it's probably just an artifact from the program/hardware. Does it do it will all atari carts?

[Chilly Willy]

You're forgetting about the half line on the last scanline. For consoles of the 8 and 16 bit era ( and other consoles too), 240p is achieved by omitting the half scanline. So you output 262 or 263 scanlines, not 262.5. This causes the TV display to place all *fields* in the exact same place and this is why you see the scanline *gap* that emulaters try to simulate - called "scanlines". Thus fields become frames.

It's not technically a legal NTSC signal (out of all the NTSC books and docs I have anyway), but almost all (99.9999999%) TVs support it.

You didn't read enough posts back. We talked about that. If you're going to comment on a thread, please read more than the last post.

@evildragon - Your TV doesn't show enough of the vertical region to see the initial scanline.

[Eke]

ok, I think I understood

so, to resume:

1/ genesis default mode is 240p (288p) and generates 262 (313) unique "superposed" lines per frame (exact framerate is unknown ?) resulting in a gap between each scanline.

313 lines in PAL is maybe because line 1 (odd field) out of 625 is drawn first on a PAL TV


2/ interlaced mode 1 is something like "240i" ("288i"): it generates 262.5 (312.5) unique interlaced lines per frame (@59.94 & 50 fps). The VDP always output the same line so, unless a line is modified between 2 fields, even and odd lines would be identical on the frame.

I wonder if any game use this mode, maybe changing the field before the whole frame is displayed could achieve a double-resolution mode in software


3/ interlaced mode 2 is 480i (576i): it generates 525 (625) unique interlaced lines per frame (@27.97 & 25 fps). In this mode, the height of the cells is doubled and the VDP alternatively outputs even and odd lines at each field (could it be inverted in PAL mode ?), resulting in a double-resolution interlaced display.

[TmEE co.(TM)]

When I set up interlace mode 1 in one of my games, it didn't seem to give anything else than a "flickery" image... best way to describe it is that it is like mode 2, but you have 240 pixel lines instead of 480... (or 224/448 for NTSC)... I haven't done any tests or anything else... no interlace looks better that it...

[evildragon]

@evildragon - Your TV doesn't show enough of the vertical region to see the initial scanline.

I can always adjusted the V-Size... (like it said, it's a video "monitor", it can be adjusted in any way I please)

[Chilly Willy]

@evildragon - Your TV doesn't show enough of the vertical region to see the initial scanline.

I can always adjusted the V-Size... (like it said, it's a video "monitor", it can be adjusted in any way I please)

That's cool. I use an Amiga 1084 monitor with my Genesis/CD/32X with a custom RGB cable. It's rather adjustable as well. I put a picture of the setup in one of the other threads recently.

[evildragon]

@evildragon - Your TV doesn't show enough of the vertical region to see the initial scanline.

I can always adjusted the V-Size... (like it said, it's a video "monitor", it can be adjusted in any way I please)

That's cool. I use an Amiga 1084 monitor with my Genesis/CD/32X with a custom RGB cable. It's rather adjustable as well. I put a picture of the setup in one of the other threads recently.

lol, mines a clone of yours. it's a Teknika MJ-22..

Has the following inputs:
Digital RGB (TTL)
Seperate Video
Composite

I'm gonna modify the digital RGB to analog RGB one of these days..

[Chilly Willy]

I can always adjusted the V-Size... (like it said, it's a video "monitor", it can be adjusted in any way I please)

That's cool. I use an Amiga 1084 monitor with my Genesis/CD/32X with a custom RGB cable. It's rather adjustable as well. I put a picture of the setup in one of the other threads recently.

lol, mines a clone of yours. it's a Teknika MJ-22..

Has the following inputs:
Digital RGB (TTL)
Seperate Video
Composite

I'm gonna modify the digital RGB to analog RGB one of these days..

Lemme tell ya - the Genesis on analog RGB is VERY nice. If you thought Kolibri was colorful before, you should see it in raw RGB. Composite video just can't handle a candle to RGB.

I used to watch TV on my 1084 as well. I made my own s-video to separate cable to use with it. A little small, but very nice picture. Not to mention, I could adjust the overscan to see most of the video transmitted. A prime example of this "safe area" being discussed in this thread - the new "The Outer Limits" series was originally made for Showtime, and featured nudity. When they sold the rights to syndication, they had to edit those scenes for broadcast TV. Some of the scenes were merely expanded or panned a little to push the nudity into the overscan area. By adjusting my monitor to see most of the overscan area, I was able to see most of the nudity that had been "edited out" for broadcast.

[evildragon]

My Genny is normally attached to my TV via Component Video, so I see the same quality pretty much, as RGB.

[Jorge Nuno]

Yes it's true, it's RGB encoded in other way (kinda like YUV)
It fact there is some very little loss, because every manipulation with analog adds noise...

Code: Select all

Y  = R + G + B + sync combined
Cb = B - Y
Cr = R - Y

It's not just summing the color components, there is a multiplicative factor before each colour [like a coeff. matrix].

[evildragon]

Y isn't just RGB combined, it's still a weighted greyscale image. (meaning blue is gonna be darker than red, and red is gonna be darker than green.. That's as simple as i can explain it).

EDIT: Oh, you sorta said that. I don't got my glasses on, can't find them.

I used a JROK RGB to Component converter, and is even powered by the 5v the AV connector outputs.