TVs & widescreen
category: general [glöplog]
This is a very simple to answer question if I try coding something instead of talking:
NTSC signal has a 720x480 resolution and supposedly only 640x480 is visible. If I want to do it in wide-screen should I use an aspect ratio of 16/9 or (640/720)*(16/9)?
NTSC signal has a 720x480 resolution and supposedly only 640x480 is visible. If I want to do it in wide-screen should I use an aspect ratio of 16/9 or (640/720)*(16/9)?
Ntsc is 640x400 visible.
I had written a long post which pouet.net has eaten :(
Anyway so, the fact you are wondering about this should tell you something about the area you consider "safe".
The NTSC standard has 525 scanlines. Of those 525 scanlines, some are taken to let the screen come back to its upwards position, so this leaves out only 480 active scanlines. Of those 480 active scanlines, we have to remove a small part (the "overscan") to be safe.
So the safe area is certainly not 640x480.
The 720x480 is actually 4:3 ratio. (Even if it does not look like it.. The pixels are not square!) The safe area is also ~4:3.
If I was sure your output signal was strictly NTSC I would say, use the width of 720 to determine the 16:9 height. However, since you might be using, say, an amiga, which is not using a standard analogue TV signal, your horizontal resolution may not be 720 in the end. (For example, in PAL mode, Amigas output a horizontal resolution of about 740 samples instead of the standard 702)
I'd advise checking what your safe area is in terms of horizontal + vertical resolution, then consider it 4:3 and derive your 16:9 height from there.
Anyway so, the fact you are wondering about this should tell you something about the area you consider "safe".
The NTSC standard has 525 scanlines. Of those 525 scanlines, some are taken to let the screen come back to its upwards position, so this leaves out only 480 active scanlines. Of those 480 active scanlines, we have to remove a small part (the "overscan") to be safe.
So the safe area is certainly not 640x480.
The 720x480 is actually 4:3 ratio. (Even if it does not look like it.. The pixels are not square!) The safe area is also ~4:3.
If I was sure your output signal was strictly NTSC I would say, use the width of 720 to determine the 16:9 height. However, since you might be using, say, an amiga, which is not using a standard analogue TV signal, your horizontal resolution may not be 720 in the end. (For example, in PAL mode, Amigas output a horizontal resolution of about 740 samples instead of the standard 702)
I'd advise checking what your safe area is in terms of horizontal + vertical resolution, then consider it 4:3 and derive your 16:9 height from there.
Thanks.
So that means that 720*480 is also 16/9, and if I have a 640*480 buffer I should use the (640/720)*(16/9) ratio.
Quote:
The 720x480 is actually 4:3 ratio.
So that means that 720*480 is also 16/9, and if I have a 640*480 buffer I should use the (640/720)*(16/9) ratio.
no.
Why are you europeans using NTSC? o.O
720*9/16 = 405
However this is not right since of course you need to take into account the pixel aspect ratio.
PAR=(480*4)/(720*3) (pixel aspect ratio width/height ~ 10:11)
- Then if your safe area is of width 640:
640*PAR/height = 16/9
<=> height/(640*PAR) = 9/16
<=> height = 9*640*PAR/16
<=> height = 320
- Then if your safe area is of width 640:
640*PAR/height = 16/9
<=> height/(640*PAR) = 9/16
<=> height = 9*640*PAR/16
<=> height = 320
Somehow, I think it's a little more complicated. At least, it is with PAL. I say that because:
Some channels here are 4:3, but show widescreen content. They have the black borders top and bottom, so the vertical resolution is less than a normal 4:3 channel. Scale them up to fill a widescreen tv, and they're visibly lower definition.
Other channels are fully 16:9, and the tv detects them as such and fills the screen. They're noticeably higher res.
I read somewhere that there's a widescreen flag you can include in the tv signal to set the tv to wide or standard, so I'm guessing that wide is using the full 4:3 res or possibly even more.
Some channels here are 4:3, but show widescreen content. They have the black borders top and bottom, so the vertical resolution is less than a normal 4:3 channel. Scale them up to fill a widescreen tv, and they're visibly lower definition.
Other channels are fully 16:9, and the tv detects them as such and fills the screen. They're noticeably higher res.
I read somewhere that there's a widescreen flag you can include in the tv signal to set the tv to wide or standard, so I'm guessing that wide is using the full 4:3 res or possibly even more.
If we're talking about standard TV signals, honestly I think they just use the blackbars to detect aspect ratio.
DVD's are another matter completly, you can encode 16:9 in a complete frame using the whole vertical resolution. (I think that's what's called anamorphic)
DVD's are another matter completly, you can encode 16:9 in a complete frame using the whole vertical resolution. (I think that's what's called anamorphic)
i need to capture videos of some of my older demos for dvd resolution and im getting quite scared with your talks. x_x
No, there IS a signal that switches the whole signal from 4:3 to 16:9 aspect ratio (hidden somewhere in the invisible scanlines together with teletext etc). Most TV stations and eg. the Xbox and Xbox 360 output it (the Wii doesn't, hence the need to set your TV manually), also most digital TV tuners generate it according to the content.
In both cases the actual resolution is about 720x480 in NTSC/PAL60 or 720x576 in PAL mode including overscan. I'd recommend subtracting a good 7.5% from all four borders for 4:3 and about 3 to 5% for 16:9 (widescreen modes seem to have less overscan), then everything should be well within the screen.
Just remember that "safe area" applies only to things you can _read_, don't make everything smaller and leave black bars around the screen please :)
In both cases the actual resolution is about 720x480 in NTSC/PAL60 or 720x576 in PAL mode including overscan. I'd recommend subtracting a good 7.5% from all four borders for 4:3 and about 3 to 5% for 16:9 (widescreen modes seem to have less overscan), then everything should be well within the screen.
Just remember that "safe area" applies only to things you can _read_, don't make everything smaller and leave black bars around the screen please :)
What KB said makes sense. Re. the 'safe area' - newer (particularly LCD/plasma) screens will just scale the image to fit the screen, so you'll get the full overscan. Older TVs will just beam the image at the screen, and if you're lucky you'll get most of the picture, if not you'll lose a random sized chunk of the edges.
So make sure anything really important is within the safe area, and for demos with text at the edges of the screen that might involve black borders so it's visible on older tvs. If there's nothing too important in the unsafe bits, use the full screen.
So make sure anything really important is within the safe area, and for demos with text at the edges of the screen that might involve black borders so it's visible on older tvs. If there's nothing too important in the unsafe bits, use the full screen.
Quote:
Just remember that "safe area" applies only to things you can _read_, don't make everything smaller and leave black bars around the screen please :)
Pah. You obviously know nothing about design.
When I do video production (for any resolution), I take the "safe area" as a 7-10% zone where I don't put anything that should be important on the video. This not only helps CRT televisions (which are not always 100% accurate on alinging the analog signal), but also badly aligned projectors/screens and many other things (apart from being design-safe and much cooler than putting stuff on the edges).
But that doesn't mean I -crop- the scene by that 7-10% (which is what I understood some of you are advicing)
But that doesn't mean I -crop- the scene by that 7-10% (which is what I understood some of you are advicing)
Actually, what's the best way of handling demo captures at 640x480? Obviously capturing at the right res is idea, but a lot of stuff is fixed at 640x480.
Is it best to keep it at that res, and have the dreaded black borders, or is it better to scale it and perhaps lose some clarity?
JCL: I advise cropping the scene (or more accurately adding black borders to expand the image) only when you have stuff at the edge of the screen (eg. if you capture an old demo - you wouldn't want to lose say a scroller off the edge of the screen. If there's nothing important in the edges, fill the screen.
Is it best to keep it at that res, and have the dreaded black borders, or is it better to scale it and perhaps lose some clarity?
JCL: I advise cropping the scene (or more accurately adding black borders to expand the image) only when you have stuff at the edge of the screen (eg. if you capture an old demo - you wouldn't want to lose say a scroller off the edge of the screen. If there's nothing important in the edges, fill the screen.
psonice, we are talking about producing the signal not capturing it.
knos: perhaps that last post wasn't too clear: I meant using captures as in using them in producing say a dvd. If you have 640x480 captures and want to put them on a dvd with 720x480 res, is it best to scale it or keep the original pixels and have borders? (or would that just squash the image so you lose the aspect ratio?)
psionice: You scale. Remember that the pixels are non-square.
In general to capture demos I would recommend capturing at the desired target frame rate (50Hz (PAL) or 60Hz (NTSC,PAL60,HD formats)) at the maximum resolution your computer and your patience can handle. Use HuffYUV or another quasi-lossless codec to keep data rates at least remotely sane.
Then (and the order of these steps is important)
1 crop to either 4:3 or 16:9 as you wish (or "anti-crop" and introduce black bars at two sides)
2 scale down to your chosen target resolution (720x480 (NTSC/PAL60), 720x576 (PAL), 1280x720 or 1920x1080) and take a note somewhere what your original aspect ratio was
3 If your destination format is interlaced (eg. for DVDs or DV), now do this:
3.1 Apply a slight blur filter in Y direction to smooth out the flickering. The amount normally depends heavily on the material you're encoding
3.2 Merge two frames into one using fields (eg. Avisynth is good for this)
4 encode using two passes and remember to set the codec settings correctly (aspect ratio, interlacing, etc)
That way you should get nice captures. This method didn't take the safe area into account tho - on-screen texts at the edge of the screen might be cut off by the screen. But adding black bars at all four sides isn't a too good solution either, so see it as informative design lesson for future demomakers ;)
In general to capture demos I would recommend capturing at the desired target frame rate (50Hz (PAL) or 60Hz (NTSC,PAL60,HD formats)) at the maximum resolution your computer and your patience can handle. Use HuffYUV or another quasi-lossless codec to keep data rates at least remotely sane.
Then (and the order of these steps is important)
1 crop to either 4:3 or 16:9 as you wish (or "anti-crop" and introduce black bars at two sides)
2 scale down to your chosen target resolution (720x480 (NTSC/PAL60), 720x576 (PAL), 1280x720 or 1920x1080) and take a note somewhere what your original aspect ratio was
3 If your destination format is interlaced (eg. for DVDs or DV), now do this:
3.1 Apply a slight blur filter in Y direction to smooth out the flickering. The amount normally depends heavily on the material you're encoding
3.2 Merge two frames into one using fields (eg. Avisynth is good for this)
4 encode using two passes and remember to set the codec settings correctly (aspect ratio, interlacing, etc)
That way you should get nice captures. This method didn't take the safe area into account tho - on-screen texts at the edge of the screen might be cut off by the screen. But adding black bars at all four sides isn't a too good solution either, so see it as informative design lesson for future demomakers ;)
Careful, HD formats are really 60Hz, NTSC is actually ~59.94Hz (the exact value is 60000/1001), and I'm not sure about PAL60 but I think it's real 60Hz too.
That's all so confusing... and to think that PAL DVD movies are running 4% faster than they should...
kb: you're talking about interlaced material there but some DVDs play at progressive scan :)
Shouldn't it be better just to make the DVDs with progressive material?
Adding to all of that your electricity (that was invented by someone's scientists) is controlled by atomic clocks with a precision of 1/10^-9.
kb: you're talking about interlaced material there but some DVDs play at progressive scan :)
Shouldn't it be better just to make the DVDs with progressive material?
Adding to all of that your electricity (that was invented by someone's scientists) is controlled by atomic clocks with a precision of 1/10^-9.
That is if you don't want your video @60Hz (or @50Hz here in Europe).
xernobyl: encoding at 25 or 29.97/30 instead for progressive DVDs is of course an option, too (don't think that DVD players can do progressive@60). But personally I've still got this good old CRT TV at home and 60Hz just looks so goddamn smooth :)
Ryg, I was pretty convinced HD format were somewhat frequency agnostic and at least supported 50hz.