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Display progressive video on an interlaced display device

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Shawn Hyper
Display progressive video on an interlaced display device
on Sep 12, 2012 at 11:21:36 am

Hi, just wonder if display progressive video on an interlaced display device, that's what we have done, is it normal that moving objects have jagged edge? Since we have noticed such jagged edge. I just thought, the display device will refresh the lines field by field, say in one filed the objects have moved ahead, but the other filed is not refreshed/updated yet, then jagged edge occurs.

Am I right? Thanks in advance.




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Rafael Amador
Re: Display progressive video on an interlaced display device
on Sep 12, 2012 at 5:32:40 pm

Progressive stuff should not have problems on any display, Interlaced or Progressive.
All the Hollywood movies are Progressive and looks OK in whatever the screen.
rafael

http://www.nagavideo.com


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Shawn Hyper
Re: Display progressive video on an interlaced display device
on Sep 13, 2012 at 12:42:08 am

Thanks for reply.

As for our case, when the object on screen is moving slowly, there's no jagged edge can be noticed. But when the object is moving fast, jagged edge occurs.

BTW, I have found an interesting tutorial which discribes such case using gif animation. The link is below:

http://neuron2.net/LVG/interlacing.html

Please check the "Progressive video on an interlaced display" gif demo.




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Rafael Amador
Re: Display progressive video on an interlaced display device
on Sep 13, 2012 at 2:17:40 am

Interlaced monitors are the best way to detect Interlacing issues. If you are seen something wrong on an InterIaced monitor is because you have some field order issue, but Progressive stuff can not cause interlacing issues.
I work only with Progressive stuff and I use an Interlaced CRT.
With an interlaced monitor you are splitting the progressive frame in two fields, but as the two fields belong to the same frame there is not difference (movement) between then.
The picture keeps looking Progressive.
Those animation are confusing. In an interlaced monitor you never see two fields at the same time.
rafael

http://www.nagavideo.com


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Shawn Hyper
Re: Display progressive video on an interlaced display device
on Sep 13, 2012 at 3:21:49 am

[Rafael Amador ]In an interlaced monitor you never see two fields at the same time.


Totally agree and that's the key point.

Suppose an object does not move at frame 1, there's no jagged edge. Then at frame 2, the object moves. The interlaced dispaly device refreshes the odd field lines first, and in this field the object has moved away from origional position, but at the same time the even field lines are waiting to be refreshed, in this field the object is still at origional position. If the object is moving slowly, the displacement between the fileds may be too small to be noticed, otherwise comes jagged edge.

Above is my personal thought.




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Rafael Amador
Re: Display progressive video on an interlaced display device
on Sep 13, 2012 at 6:02:13 am

Shawn.

You are describing how LCD works.
CRT screens works completely different. CRTs have no "pixels".
In a CRT computer you are seen just on single dot of light moving very fast from left to right and from tot to down. Is one single beam of electrons what hits one phosphor at a time. Is our eyes/brain what makes us to see a full picture.
In CRTs do not exists the kind of refresh of the LCDs and other computer screens. On those all the pixels are lighted at the same time, and the whole picture is displayed/refreshed at once.
When you play interlaced stuff on a computer screen, the interlaced shows up because both fields are display at the same time.
But whatever the kind of screen, when you play the two field of a Progressive picture -both at the same time if is an LCD, or one after the other if a CRT- there is no difference between them so it can not show any kind of interlacing artifacts.
rafael

http://www.nagavideo.com


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Shawn Hyper
Re: Display progressive video on an interlaced display device
on Sep 15, 2012 at 5:49:37 am

[Rafael In a CRT computer you are seen just on single dot of light moving very fast from left to right and from tot to down. Is one single beam of electrons what hits one phosphor at a time. Is our eyes/brain what makes us to see a full picture.


Yes, agree. But CRT monitor does not scan the whole frame from top to bottom line by line. It will scan the odd field lines first then the even field lines, right? Is so, there's time difference between the updating of the two field, 1/50 second in PAL. Then, while the CRT monitor updating odd filed lines, here the object is away from origional position, the even field lines are not updated, here the object is still at origional position.




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Rafael Amador
Re: Display progressive video on an interlaced display device
on Sep 15, 2012 at 4:28:43 pm

[Shawn Hyper] "Yes, agree. But CRT monitor does not scan the whole frame from top to bottom line by line. It will scan the odd field lines first then the even field lines, right? Is so, there's time difference between the updating of the two field, 1/50 second in PAL. Then, while the CRT monitor updating odd filed lines, here the object is away from origional position, the even field lines are not updated, here the object is still at origional position."
Shawn,
In an LCD monitor, the pixels are emitting light until they are "updated", and your seen the 480 (576 PAL), 720 or 1080 lines of your picture all at the same time, therefor when you play interlaced material you see both fields at the same time and looks like crap.

In a CRT, when the beam of electrons hit a phosphor, the phosphor lights up and immediately starts to dims down, so before the beam hits the same spots again, that dot is not emitting any light. When the lines of one field are "projected" his light conceals the remaining of the field before. You never really see the two fields at the time. is an optical illusion. The fields are wrote so fast that your eyes can't see the in-between empty lines.
When you see one field, the field before is only in your brain. That's call temporal integration.
When you watch a movie (24fps) in a movie theater, each frame is projected twice, and whit a black in the in between. So you see:
Picture A - Black - Picture A - Black - Picture B - Black - Picture B - Black - Picture C...
But, do you see any black when you watch the movie?
rafael

http://www.nagavideo.com


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Shawn Hyper
Re: Display progressive video on an interlaced display device
on Sep 19, 2012 at 12:20:50 am

Got it. Thanks a lot for your patient explaination.




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