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Is standard broadcast 525i or 480i?


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22 replies to this topic

#1 of 23 OFFLINE   Ken Burkstrum

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Posted April 18 2006 - 03:11 PM

If it's true, im wondering why broadcast looks worse then DVD?

#2 of 23 OFFLINE   Joseph DeMartino

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Posted April 21 2006 - 05:34 AM

Each NTSC frame consists of 486 lines out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning). That's the maximum resolution. Then you have to consider the source material, e/m interference in broadcast signals, compression in network satellite distribution, DBS retransmission, cable delivery, and a whole host of other things that can conspire to reduce the overall picture quality of "regular" TV. It isn't all about resolution. A lousy video tape played back on an HD channel would look worse than on an SD channel, because the HD broadcast would show the flaws more clearly

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#3 of 23 OFFLINE   JeremyErwin

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Posted April 21 2006 - 07:25 AM

analog broadcast tv (ntsc) has a flawed color model. It's 480i, but it's inferior to dvd or non-bitstarved sdtv

#4 of 23 OFFLINE   Ken Chan

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Posted April 21 2006 - 08:22 AM

And it's not just the number of lines, it's also the amount of detail per line. VHS has the same as broadcast and DVD, but it looks worse than both. Laserdisc too, but it is between broadcast and DVD.

#5 of 23 OFFLINE   Ken Chan

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Posted April 21 2006 - 08:26 AM

dupe

#6 of 23 OFFLINE   ChrisWiggles

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Posted April 23 2006 - 04:46 AM

Broadcast is crippled by many factors including just plain noise via broadcasting, it's often bounced around by satellite heavily compressed before it even gets broadcast locally to you, so you can get tons of banding and crap that way, MPEG blockin artifacts and all that. Also, as mentioned above, it is composite NTSC, while DVD is YCbCr, so DVD has a significant advantage there.

#7 of 23 OFFLINE   Michael TLV

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Posted April 23 2006 - 05:11 AM

Greetings

Broadcast has more horizontal resolution compared to VHS but less than DVD. Roughly 100 more lines versus VHS and 200 less lines versus DVD.

A pristine NTSC broadcast signal from a satellite looked close to Laserdisc quality ... but you'd only see it if you had a big ugly dish.

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#8 of 23 OFFLINE   Ken Burkstrum

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Posted April 23 2006 - 09:03 AM

I thought VHS was 320x240?

"Broadcast has more horizontal resolution compared to VHS but less than DVD. Roughly 100 more lines versus VHS and 200 less lines versus DVD."

Can you give me exact numbers?

So broadcasted HD gets some of the same interference as standard broadcast yet is still preferable to playing a DVD in your home with a dvd player?

Why would VHS look worse on a hd tv then on a sd tv, I figured despite any scaling they would look pretty much the same, like crap!

#9 of 23 OFFLINE   JeremyErwin

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Posted April 23 2006 - 09:53 AM

so many questions.

Let's start with resolution. With analog, there's no fixed horizontal resolution. It varies from set to set, and signal to signal. To measure horizontal resolution, the engineer throws up a test pattern, and counts the number of discernible lines.

However, because of the way the signal is generated, there's always a standard number of scanlines, most of which hold picture data.

Analog 480i uses 525 scanlines.
Analog 720p (yes, if you use a RGB monitor and a tuner with a SVGA port, you can receive this...) uses 750 scanlines.
Analog 1080i uses 1125 scanlines. (Japan had a analog HDTV system at one time)

However, if you use a digital system to display or transmit a video signal, the horizontal resolution is defined. Both mpeg frames and LCD displays consists of a fixed number of picture elements.

SDTV (480i) is 480x720.
HDTV (720p) is 720x1280
HDTV(1080i) is 1088x1920.

DVDs store their picture at a variety of resolutions (640x480, 704x480, 720x480).

So when someone says that VHS has a resolution of 240 lines, they mean that only 240 vertical black and white stripes can be distinguished. Any higher, and it all turns into a grey blur. Laserdisc is capable of about 500 lines of resolution. Both, however, display 525 scanlines (interlaced).

There's a couple of ringers to toss in though. When measuring resolution, many (most?) measurements only care about a circular area of the screen. So, those 500 lines of resolution quoted for laserdisc may mean that the signal, when captured digitally, is best captured by a 665x480 digital frame.

But analog television is dead, dead, dead.

A common projector advocated on this forum is the Infocus 4085. It is a 16:9 projector, and it has a 480x852 (IIRC) element display. Some people have had some success sending a 720x1280 scaled image to the projector, thus taking advantage of the extra horizontal resolution of this display.

Throw is color resolution and it gets even dicier.

#10 of 23 OFFLINE   Ken Burkstrum

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Posted April 23 2006 - 06:05 PM

I'm confused what the difference between digital and film is because they both seem to be captured on tapes as far as I understand it. So your saying VHS film isnt made out of pixels and scanlines and that it's quality is comparable to 240 scanlines?

#11 of 23 OFFLINE   JeremyErwin

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Posted April 23 2006 - 06:37 PM

VHS isn't film. It's magnetic tape. And it's generally analog (the exception being DVHS, which records mpeg2).

You're confusing lines of resolution (columns) with scanlines (rows). Vhs, laserdisc, ntsc, dvd, all have the same number of scanlines (486). The number of lines of resolution varies from device to device.

and, why, for the love of ... are we discussing vhs? vhs is obsolete. Gone. Forgotten. Even DVHS has been largely replaced by hard disc recordings and now HD-DVD.

#12 of 23 OFFLINE   Michael TLV

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Posted April 24 2006 - 03:28 AM

Greetings

All horizontal numbers are expressed as lines per picture height. A square.

VHS was 240 lines
Broadcast was 340-350 lines
Laserdisc was 375-425 lines
SVHS was 400 lines
DVD is 540 lines

VHS looks crappy on HD sets because of the lack of scan line structures. Our brain interprets a sharper image when visible scanlines are present in an image.

An interlaced picture of a white wall devoid of detail will look more detailed / sharper than a progressive scan image of the same white wall.

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Michael @ The Laser Video Experience
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#13 of 23 OFFLINE   Allan Jayne

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Posted April 24 2006 - 06:06 AM

Both 525i and 480i are used to refer to the same thing in analog video.

For digital 480i video including DVD only 480 of the 486 picture containing lines are kept and lines 487 through 525 are not recorded on the disk either. For outputting an analog signal including component video the player adds back in scan lines 481 through 525 for both 480i and 480p. The various digital video formats SDMI and DVI and the way the data is recorded on DVD also have something between scan line 480 and the next frame's scan line 1 but this block of data is not organized as a fixed number of additional scan lines.

Analog video is pixellated in the vertical direction only. If you were to take an upright thin cross section you may well see the cross section divided up into 480 or 486 pixels (720 or 1080 for HDTV). Digitial video including DVD is pixellated both horizontally and vertically.

Video hints:
http://members.aol.c...nejr/vidres.htm
.

#14 of 23 OFFLINE   Ken Chan

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Posted April 24 2006 - 12:18 PM

Quote:
So broadcasted HD gets some of the same interference as standard broadcast yet is still preferable to playing a DVD in your home with a dvd player?
HD (as it is now in the U.S.) is digital, and digital is resistant to interference. With analog, you get ghosting or snow or buzzing or whatever, progressively worse with more interference. With digital, the picture stays the same, up until it turns into a complete mash of green squares or disappears completely. So even with some interference, it is likely to be "perfect" most of the time. And if they're both perfect, the resolution of HD is much higher than DVD, so HD is better.

Quote:
DVDs store their picture at a variety of resolutions (640x480, 704x480, 720x480)
352x480, not 640x480.

#15 of 23 OFFLINE   JeremyErwin

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Posted April 24 2006 - 01:21 PM

Quote:
352x480, not 640x480.

I stand corrected. The nicest thing about atsc, imho, is that it doesn't have ntsc's broken color model.

#16 of 23 OFFLINE   Allan Jayne

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Posted May 18 2006 - 07:55 AM

What shows are recorded on DVD as 352 pixels across (by 480 high)?

They must look awfully blurry.
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#17 of 23 OFFLINE   Ken Chan

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Posted May 19 2006 - 12:04 PM

They are blurry. I don't know of any DVDs that are sold that way, but it's in the spec, and it works. The big thing is you can get about twice as much stuff on a disc. Maybe if you're transfering from VHS, it makes the bad only slightly worse. Come to think of it, maybe some DVD-recorders use it for their long-play setting.

#18 of 23 OFFLINE   ChrisWiggles

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Posted May 19 2006 - 05:31 PM

Quote:
Analog video is pixellated in the vertical direction only. If you were to take an upright thin cross section you may well see the cross section divided up into 480 or 486 pixels (720 or 1080 for HDTV). Digitial video including DVD is pixellated both horizontally and vertically.

This is misleading, IMO. All video is sampled in both directions. I also would refrain from using "pixel" terminology, but rather image sampling. Pixels is a slightly confused term.

#19 of 23 OFFLINE   MarkHastings

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Posted May 20 2006 - 05:01 PM

Quote:
What shows are recorded on DVD as 352 pixels across (by 480 high)?
Is 352x480 the DVD spec? I thought it was an MPEG spec?

Anyways, you find that spec mostly with DVR's - That's how you get more shows recorded onto the hard drive.

Also, VOD (Video On Demand) is often recorded to sizes lower than 720x480 to make it easier to deliver.

#20 of 23 OFFLINE   Steve Berger

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Posted May 21 2006 - 03:41 AM

Quote:
Originally Posted by MarkHastings
Is 352x480 the DVD spec?....VOD (Video On Demand) is often recorded to sizes lower than 720x480 to make it easier to deliver.
352x480 and 720x480 are in the DVD spec (I think 704x480 is also but I'm not positive). Consequently most authoring programs will make DVDs from them quite nicely.

Since 352x480 is better than most consumer tape formats and slightly better than the typical analog broadcast available, it is, in theory, a good choice for recording those things.

The VOD (528x480 and 540x480 commonly) allow reduced bandwidth for transmission but the files generally need transcoding (or header changes) to create DVDs. Digital camcorders (at 720x576) also require similar jiggering to create DVDs.

DVRs use various resolutions and bitrates but are fairly secretive about it. You find out when you examine the files created. Some of the flex recordings can even change during the recording process, as I understand it, making DVD creation really tough (if you can extract the files).


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