interlace help

[nymph4444]

I know NTSC resalotion 525 but you can only see 480
But what do you meen it was 486 and then they changed it to 480?
If it was 486 that you could see why change it to less 480?

[edDV]

I know NTSC resalotion 525 but you can only see 480
But what do you meen it was 486 and then they changed it to 480?
If it was 486 that you could see why change it to less 480?

Because when digital video started, 640x480 frame buffers were more cost effective for memory. In the late 80's early 90's memory was far more expensive than today. At first the FCC held to 486 lines. Eventually they decided this minor letterbox was a creative rather than technical issue.

After that decision, digital standards (including MPeg2, DVD and ATSC) settled on 480 lines for SD digital video.

[jagabo]

The electron beam of a CRT scans slightly diagonally. The topmost scanline is really only half a scanline (the right half) and the bottommost scanline is only half a scanline (the left half). The active picture region of a CRT is actually 485 scan lines. Since computers like rectangular arrays the top and bottom half lines are stored as full lines, giving 486 lines. But since televisions overscan only about 440 of those lines is typically visible. So it was decided to use 480 as that's a nice mod 16 number.

http://www.pembers.freeserve.co.uk/World-TV-Standards/Line-Standards.html

Examine the "vertical timing" section:

http://www.pembers.freeserve.co.uk/World-TV-Standards/Line-Standards.html#Vertical

[nymph4444]

Now I have been doing some reading on Interlaced Images and I think I have it now?

Say you are watching a person talking on TV you will see this.

Say the person is standing up I read that when the first field is drawn on screen it is Half the image like you say.

But they say it reay looks like Half the Hight of the person.

So do you only see from the Head to Hipps and then the next Field draws the Legs and feet?

[manono]

Now I have been doing some reading on Interlaced Images and I think I have it now?

As near as I can tell, you have nothing. You haven't learned a thing. You've done no research at all and expect these 2 fine people to hand it all to you.

So do you only see from the Head to Hipps and then the next Field draws the Legs and feet?

Hardly. Here, go and read from this page:

http://www.hometheaterhifi.com/volume_7_4/dvd-benchmark-part-5-progressive-10-2000.html

Scroll down from the top and begin at The Nature of Interlaced TV, Film-to-Video Conversion, and Other Interesting Gambits. Note the little video right below that (Interlaced NTSC TV/Field 1/Field 2/Interlace Scan) showing how interlaced images are drawn on a CRT Television. Read down through Re-Interleaving 24fps Film. Then read the whole thing again. And again. Until it begins to sink in. You might even read the rest of the page to learn about other related subjects. And stop wasting these people's time unless and until you've actually done some research of your own and there's something specific you don't understand.

[jagabo]

So do you only see from the Head to Hipps and then the next Field draws the Legs and feet?

No. One field is all the even numbered scanlines, one all the odd numbered scanlines. So each field covers the entire height of the frame, but only ever-other scanline. Using edDV's image from earlier:

This interlaced frame of video:


contains two fields:




Click on the images to view them full size. Note how each image only contains half the picture. There is a black line between each line of picture information. It's a little hard to tell looking at two separate image but when when you switch back and forth between them you can see that the car has moved between the two fields:


Again, click on the image to see it full size and animated.

[nymph4444]

OK I whent to the link and have this understanding.

NTSC = 30 FPS and every Frame is made up of Two Fields.

First all the Od Lines are drawn and this makes up one singal image alone.

Then as all the Od Lines start to Fade all the Even Lines are drawn.

And the two Fields onscreen make One Frame.

So If I understand it right if you are watching some one walking if we could slow it down we would see every little movment is it's own Field.

Because every Field is it's own Image?
Do I have this part down?

[edDV]

OK I whent to the link and have this understanding.

NTSC = 30 FPS and every Frame is made up of Two Fields.

First all the Od Lines are drawn and this makes up one singal image alone.

Then as all the Od Lines start to Fade all the Even Lines are drawn.

And the two Fields onscreen make One Frame.

So If I understand it right if you are watching some one walking if we could slow it down we would see every little movment is it's own Field.

Because every Field is it's own Image?
Do I have this part down?

On a computer you will see both fields that make up the frame. Hence the double image for telecine frames 2 and 3. Click on Jagabo's last image above. He is showing both fields alternating so you can see there is motion from field 1 to field 2. The reason the picture goes dark is half the lines are black when you separate the fields.

You need to understand interlace if you want to understand digital video. It is a difficult concept but fundamental. Everything builds from there. DVD is basically an interlace format with progressive extensions. You won't begin to understand Blu-Ray or HDTV until you first master SD interlace.

The article manono linked has been greatly improved since I last read it. It is a very good introduction to interlace and the DVD format.

[jagabo]

OK I whent to the link and have this understanding.

NTSC = 30 FPS and every Frame is made up of Two Fields.

There are no frames in analog NTSC video. Only fields. 59.94 fields per second. It's only after digitizing the video that it is stored as frames, 29.97 interlaced frames per second.

First all the Od Lines are drawn and this makes up one singal image alone.

Then as all the Od Lines start to Fade all the Even Lines are drawn.

Yes.

And the two Fields onscreen make One Frame.

There are no frames in analog NTSC video.

So If I understand it right if you are watching some one walking if we could slow it down we would see every little movment is it's own Field.

Yes.

Because every Field is it's own Image?
Do I have this part down?

Yes.

[nymph4444]

I think it is me how I am wording it to you.

When I look at the photo of the Car I see all the Od Lines and I do see it looks like there is every other Line is Black because it did not draw that in yet.

This is what I ment when it draws the Even Lines this is the Next Field and every Field is it's own image?

[edDV]

I think it is me how I am wording it to you.

When I look at the photo of the Car I see all the Od Lines and I do see it looks like there is every other Line is Black because it did not draw that in yet.

This is what I ment when it draws the Even Lines this is the Next Field and every Field is it's own image?

An interlace field is not intended to be a separate image, a field has half the lines missing. It is part of a sequece of fields that make a TV field sequence. If you must pause interlace, there are different techniques that can be used.

You are confusing analog video with digital. In digital, fields are identifyed to a frame. Remenber all the TFF/BFF discussion?

Then you are confusing interlace CRT displays with computer monitors. After several requests, you won't tell us what type of TV is connected to your media player. If the TV is interlace, the media player must export interlace.

[nymph4444]

I think I was confusing Digatle with Analog.

I am soory I am just talkinjg about Analog CTSC CRT TVs

I think I get it now that I whent back and looked at the photo of the Car.
Let me gess tell me on an Analog CRT TV if I did look at the two Fields togather it would look Blury am I right?

[edDV]

I think I was confusing Digatle with Analog.

I am soory I am just talkinjg about Analog CTSC CRT TVs

I think I get it now that I whent back and looked at the photo of the Car.
Let me gess tell me on an Analog CRT TV if I did look at the two Fields togather it would look Blury am I right?

NO. Analog interlace CRT TV sets can only display one field at a time. In continuous motion, one field will be wriiten while the previous field is fading but if you stop the play (e.g. pause on an old vcr) you will only see one field. There is no reason the still would be blurry unless it is processed in some way.

Explain the connection from your media player to TV. Is it composite or S-Video? In either case, it would be interlace 480 lines interlace at 59.94 fields per second.

[jagabo]

Analog interlace CRT TV sets can only display one field at a time. In continuous motion, one field will be wriiten while the previous field is fading but if you stop the play (e.g. pause on an old vcr) you will only see one field.

I've seen a few DVD players (and I'm pretty sure I've seen it with VHS decks too) that continue to send both fields (alternately). In that case you see an image that bounces back and forth like the the GIF I uploaded earlier (much faster of course).

[edDV]

Analog interlace CRT TV sets can only display one field at a time. In continuous motion, one field will be wriiten while the previous field is fading but if you stop the play (e.g. pause on an old vcr) you will only see one field.

I've seen a few DVD players (and I'm pretty sure I've seen it with VHS decks too) that continue to send both fields (alternately). In that case you see an image that bounces back and forth like the the GIF I uploaded earlier (much faster of course).

Yes there are many ways a VCR player could display a pause. The early ones stopped on a field, or if the player had a frame buffer they showed two fields flickering. More sophisticated VCR players would apply a field 1 to field 2 copy to a frame buffer (half vertical resolution) to show a stable stopped field. Next step up for VCR players was a simple blend deinterlce still. This showed better vertical resolution (less diagonal stepping). Progressive DVD players stepped in at this level.

The DVD players you describe probably had no deinterlace processing.

[edDV]

I think I was confusing Digatle with Analog.

I am soory I am just talkinjg about Analog CTSC CRT TVs

I think I get it now that I whent back and looked at the photo of the Car.
Let me gess tell me on an Analog CRT TV if I did look at the two Fields togather it would look Blury am I right?

OK for analog we need to separate source file issues from display hardware issues.

You can't look at two fields together on an analog CRT monitor. It is a field by field stream.

Keep asking questions.


PS: I'm sympathetic because it was difficult for me to "get it" too. Keep it up.

Rest assured less than 20% sort of get it here. Less than 5% really get it. The main thing is you want to know.

[nymph4444]

My TV is a 60 ich Projection Set and I have a None Prograsive DVD Player and it conects with RCA Composit Jacks.

I am not at all talking about my DVD Player or my Projection TV I am just talking about CRT Broadcasting.

And yes I do know now and understand that One Field is it's own image and you can not see just One Field alone.
Because as one Field is being drawn the Field before it is Fading but your eye can't see it.

I get all of thiis what I sould have asked is If you could see the two Fields togather it would look Blury because it was only ment to see One Field at a Time Right?

[jagabo]

what I sould have asked is If you could see the two Fields togather it would look Blury because it was only ment to see One Field at a Time Right?

If there is no motion the picture will be perfectly clear. If motions are small there will be a little blurring, or you will see comb artifacts. If motions are large it will look like a double exposure, or you will see comb artifacts.

[nymph4444]

Thank you that is what I ment if there was any movment and you could see both Fields on screen you would see Blury because every frame is it's own image.

Now just one thing if every Field is it's own image and just say there is movment and you could stop it at just one Field am I right you would see a Grany Image because one Field will be missing the other Field witch is every other Line?

[edDV]

Thank you that is what I ment if there was any movment and you could see both Fields on screen you would see Blury because every frame is it's own image.

Now just one thing if every Field is it's own image and just say there is movment and you could stop it at just one Field am I right you would see a Grany Image because one Field will be missing the other Field witch is every other Line?

An NTSC CRT TV displays a sequence of fields. For normal interlace (non-film) video like TV news, sports or talk shows, each field will show a motion update. As each new field is scanned, there is some remainder of the previous field as the phosphor fades away. The eye/brain will perceive this as continuous motion.

Telecined film interlace video is different. It is also a sequnce of fields but motion is not continuous due to the 3 field 2 field representation of the film frames. This uneven motion is called judder. For example, a slow pan will appear to alternate fast-slow-fast-slow. Zooms will also show jerky motion. For these reasons pans and zooms are mostly avoided when shooting a TV series on film.

Other types of displays use different techniques to display interlace video. Projectors vary in technology. What is your projector model? Plasma and LCD displays are progressive so must show interlace as a sequence of frames rather than fields. Normal 60i interlace video will be deinterlaced to 60p or 120p. Telecine video will be inverse telecined to 60p or 120p for display.

[edDV]

Now just one thing if every Field is it's own image and just say there is movment and you could stop it at just one Field am I right you would see a Grany Image because one Field will be missing the other Field witch is every other Line?

You can't pause an interlace CRT TV but if you have a digital camera, you can take a picture of the screen with shutter set to 1/60th second. This will show a single field, or more likely parts of both fields being scanned. Take several pictures to get a sense of the scan pattern. It is important you shoot this from a tripod with sharp focus on the screen.

[nymph4444]

Well this is what I ment.

I have some VHS Tapes of movies from the 1990's and I have a 4. Head VCR.
So when I hit the Pause the Tape say one a persons Face it looks Clear.

Now I know what you are telling me that every Field is it's own image so every little movment will be on it's own Field.
And if you happen to get the two Field on screen at one time and there is movement you will see a little bit of what will look like two images togather.

I get all of this but some times even with Movment when I pause the Tape it looks Clear.

I just always thought you would see Lines through the Image?

[edDV]

A conventional VCR pause is just playing a single field over and over and sent as odd and even lines to prevent the screen from going half brightness. Vertical resolution will be half. A two head VCR will show the head switch noise in the picture, a four head VCR will cover the head switch area. Still you are only looking at a single field played as odd and even lines.

More sophisticated VCR's will have a frame buffer that allows a two field frame freeze. Some of these will deinterlace to progressive for the still*. This kind of technology is common in progressive DVD players.

The only way I know to see a single CRT field scan is by photgraphing the TV with 1/60th or higher shutter speed.


*The old Sony analog Mavica video printers evolved into a line of industrial/medical video still image printers. Until recently, most cameras used for medical imaging were interlace.

[nymph4444]

Now I have a Free program called Media Coder to convert Video Files to other file types.

Now when I open my VOB Files of Decrypted from my DVDs of the Land Of The Lost TV show it tells the specas of the file.

And it tells me the File is Interlaced Video.

So when I convert it to mp4 H264 I would think I would have to Interlace it.

But am I right that all that would do is try to Interlace an already Interlaced video?

[edDV]

Now I have a Free program called Media Coder to convert Video Files to other file types.

Now when I open my VOB Files of Decrypted from my DVDs of the Land Of The Lost TV show it tells the specas of the file.

And it tells me the File is Interlaced Video.

So when I convert it to mp4 H264 I would think I would have to Interlace it.

But am I right that all that would do is try to Interlace an already Interlaced video?

In Handbreak, interlace in remains interlace with all filters turned off.

480i MPeg2 in ---> 480i h.264 out

Other modes

480i MPeg2 in --> deinterlace or decomb filters --> 480p h.264 @ 29.97 or 59.94 fps out

Or for a typical movie,

480i (telcine) MPeg2 in --> detelecine filter --> 480p h.264 @ 23.976 fps out


For a progressive DVD, there is a straight conversion to h.264 (all filters off)

480p MPeg2 in --> 480p h.264 @ 23.976 fps out

[nymph4444]

I am sorry I typed to fast I ment to say

I have DVD's of the 1970's TV Show The Land Of The Lost
and I Decrypted some of the VOB files and put them on my Hard Drive.

Now eatch One is about 1.5 GB or so and I was going to convert them to MP4 H264 at a Low bit rate because MP4 H264 gives good video picture at Low bit rates.

You say In Handbrake Interlace remains Interlace.

Please explaine?

If you mean you can turn off if you want to Interlace or De Interlace your video files you convert I think I can turn them off in Media Coder if this is what you are saying?

Please tell

[edDV]

I am sorry I typed to fast I ment to say

I have DVD's of the 1970's TV Show The Land Of The Lost
and I Decrypted some of the VOB files and put them on my Hard Drive.

Now eatch One is about 1.5 GB or so and I was going to convert them to MP4 H264 at a Low bit rate because MP4 H264 gives good video picture at Low bit rates.

You say In Handbrake Interlace remains Interlace.

Please explaine?

If you mean you can turn off if you want to Interlace or De Interlace your video files you convert I think I can turn them off in Media Coder if this is what you are saying?

Please tell

No I was explaining the user interface.

How do you want to play these files? With your media player and projector? If so, why not play the VOB?

In other words, what are you trying to do?

[nymph4444]

Well I have a Match Speed Trio 500 media player with a 5 inch LCD screen.

If I put the VOB file on it as is it plays ok why?
I thought LCDs were not Interlaced?

And 2. the player can be connected to an HDMi port on a TV. And for that I realy thought you could not play Interlaced video?

Please tell me what is going on with my Trio why it can play interlaced video on the LCD screen

[jagabo]

Well I have a Match Speed Trio 500 media player with a 5 inch LCD screen.

If I put the VOB file on it as is it plays ok why?
I thought LCDs were not Interlaced?

Because the designers of DVD players and LCD displays know what they're doing. They know how to handle interlaced video -- they deinterlace it.

And 2. the player can be connected to an HDMi port on a TV. And for that I realy thought you could not play Interlaced video?

It's the same with all DVD players and TVs: they know how to deal with interlaced video. They deinterlace it if necessary.

[nymph4444]

Soory I have a Trio 5000 Model.

I think you just helped me out with something.

I Took some of my VOB files of TV show and Movies and when I converted them to mp4 H264 I tryed Interlaceing options and De Interlaceing options.

And when I played it on my Computer or on my Trio 500 the video would play in two full dabble images.
The top half of the screen woul play the same video that played at the bottum of the screen.

And I think I get it now if I take a VOB file that is Interlaced I sould just leave it as is. I thought I had to Interlace it again when I convert it.
But what I was realy doing is Interlacing a video that was Interlaced to start with.
So it played massed up because I was giveing it another Interlaceing am I right on this?

And the same thing if I convert a VOB of a movie I sould not be trying to give it a Interlace or De Interlace because if it had it I am doing it again.

So if I am right De Interlaceing and or Interlaceing sould just be at the making of things and or Broadcasting. Not to be doen again later.

So if my Trio 5000 can play VOB files it know they may be Interlaced and if I do an Interlace of an Interlaced video and put it on my Trio 5000 it wont know how to handle it and the playback is OFF.

Am I right or do I still not have it