Progresive video on a TV

[Pete Harris]

Hi
New to the Forum, but have a question on interlacing.I currently edit in Avid & then output as a quicktime reference file & the encode in TMPGenc, now if I deinterlace the video & encode in progresive mode will the video play ok on a normal TV (PAL). On my monitor the video looks great, but its progresive so what willn the result be on TV. I ask this as I film in PAL & live in States but have family in New Zealand so have no real way of testing.

Cheers Pete

[David Jimerson]

How are you planning to deliver it to watch on a TV?

If on tape, it will be re-interlaced before it goes to tape. It should still look progressive, but it will be interlaced.

If on DVD, it will either be re-interlaced before it goes to DVD, or it will be progressive on DVD and the DVD player will re-interlace it before it goes to the TV. Again, it will still look progressive.

[Robert Bobson]

If you view a progressive video on an interlaced TV, you will still see interlaced "jaggies" on motion when the second field of one frame is replaced by the first field of the next frame.

But there will only be half the number of these "motion jaggies" as there are in full interlaced - 60i.

[David Jimerson]

You won't see the jaggies on an interlaced TV -- only one field visible at a time.

[Robert Bobson]

I believe that you will see jaggies because that's the way interlaced works.

each progressive frame is broken down into two fields (no jaggies between them), but then when the first field of the pair is redrawn with the first field of the next pair, motion jaggies are created.

You won't see jaggies with a PROGRESSIVE TELEVISION SET that draws all the lines of a frame at once, and then replaces all these lines with all the lines of the next frame.

[David Jimerson]

The only time you see jaggies is when you're watching interlaced footage on a progressive screen (which includes 24p footage being viewed on a 60i timeline), because you've got both fields onscreen at once -- so you see a comb-like interlace artifact in moving objects, because they're two places at once on the screen.

An interlaced TV screen shows only one field at a time -- only one moment in time at a time. When it moves from the last field made out of one frame to the first field made out of the next frame, it's no different from moving between any two fields of interlaced footage. They're not on the screen at the same time, so there's no possiblity of jaggies.

Do Hollywood DVDs produce "jaggies" on an interlaced TV? (No.) They're all progressive.

[Pete Harris]

Thanks everyone for your input.The video will be on DVD & if I get this right Progresive is it.

Thanks again
Pete

[Robert Bobson]

[David Jimerson wrote:

An interlaced TV screen shows only one field at a time -- only one moment in time at a time. When it moves from the last field made out of one frame to the first field made out of the next frame, it's no different from moving between any two fields of interlaced footage]

Not to sound contentious, but interlaced tv DOES NOT show only one field at a time - That's why it's an interlaced tv!

field "A" (odd lines) is drawn on the screen, then field "B" (even lines) is drawn in between the odd lines. Then the next field "A" is drawn in between the even lines, and so on.

So yes, two different fields are ALWAYS ON THE SCREEN AT THE SAME TIME.

and if you watch a progressive movie on an interlaced tv, you will see jaggies that you won't see if you watch the same show on a progressive tv or on a computer monitor.

[David Jimerson]

Robert, if that were true, every single frame of interlaced would have have the jaggies, if there's motion, because every single field is from a different moment time.

Interlace relies on "persistence of vision" -- it looks like a whole picture because your brain retains an image for an instant after it disappears.

But there's only one field on the screen at a time.

[David Kennett]

I did something sometime ago that really brought home the unique advantage of interlaced scanning WHEN SHOWN ON AN INTERLACED DISPLAY.

I was editing DV on computer, and had need for a freeze frame. I chose a frame with little motion, thinking that I would not need to de-interlace for the freeze. The only motion was a hand moving slightly near the bottom of the frame, and on the progressive computer screen, the hand became serrated, as the two fields blended together. This was not the center of attention, and was hardly noticeable.

Imagine my surprise when I first saw the freeze on interlaced TV! The hand was no longer serrated, but fluttered back and forth. The moving hand then became the center of attention.

Interlaced video on an interlaced display works beautifully because we see the MOTION taking place between the two fields. All this benefit is lost when we convert either direction.

[Markus Bo]

Hi guys,

is there any way to proceed from progressive filming to good interlaced. I am quite frustrated trying it with Avid Liquid but the result ist bad. My Cam JVC HD101 does a fantastic conversion via composite or component out but I will do it after Editing. Any idea?

Markus

[Robert Bobson]

Dave wrote: if that were true, every single frame of interlaced would have have the jaggies, if there's motion, because every single field is from a different moment time.

Interlace relies on "persistence of vision" -- it looks like a whole picture because your brain retains an image for an instant after it disappears.

But there's only one field on the screen at a time.

David, you're not correct. you could just as easily say "because of persistence of vision, there's only one line on the screen at a time" or "there's only one pixel on the screen at a time".

but the fact is we "see" two fields at the same time, until the first field is scanned over with the "third" field.

in progressive 30p, every single field isn't from a different moment in time.
each frame is made up of two matching fields, because there are only 30 unique images per second - so there's no motion artifacts between these two identical fields.

but there will be motion jaggies between the 2nd field in a matching pair, and the first field in the next matching pair (as long as there's motion in the image)

even with 2:3 pulldown, the majority of frames are made up of matching fields. again, no motion jaggies on these frames.

anybody else want to wade in here with their opinion?

[David Jimerson]

Robert, think about what you're saying.

I'm not talking about progressive video here; I'm talking about interlaced video. 60i.

You're saying that interlaced TVs work by drawing in Field 1, then drawing in Field 2 in between the lines of Field 1 while Field 1 is still on the screen. Then, Field 3 comes along and erases Field 1 and Field 2, then Field 4 is drawn in between the lines of Field 3, still on screen. And so on.

Field 1 of the video is one moment in time. Field 2 is the next 1/60th of a second. Two different moments in time. And so on with Field 3, Field 4, Field 5, Field 6, etc.. Every single "frame" made up of these fields would have the comb artifiacts if both fields were on screen at the same time -- if there's motion.

Also, if it worked with progressive video the way you say, then most of what you see on TV would have the jaggies, because most of it is shot either on film (as progressive as it gets) or on 24p video -- all the TV dramas, movies, most sitcoms, high-budget commercials . . . and a lot of "reality" shows are shot in 30p, and sometimes in 24p. But none of it has the jaggies.

Which circles back to the original point -- progressive video looks just fine on an interlaced TV.

For further reading, please check out:

http://en.wikipedia.org/wiki/Interlaced

http://www.digitalfaq.com/dvdguides/...tandsource.htm

[Robert Bobson]

Yes, 60i has 60 different moments (fields) per second. and if there is motion on the screen, there will be jaggies visible between every field.

But we were talking about progressive video. and there will be jaggies between each "different" field in motion.

I am sure of what I'm saying. I've worked in television for 25 years.
I know television inside and out.

If, as you say, only one field were visible at a time, the lines that make up the other field of that frame would be black? that's not correct.

If you were to freeze off any frame (two fields) containing motion from any television show broadcast in interlaced video, you will see jaggies!!

and any movie originally shot on film, soap opera, news program, expensive commercial - ALL CONTAIN JAGGIES WHEN BROADCAST INTERLACED!

That why photoshop has a deinterlace filter - so that you can eliminate one of the fields if you're using a freeze for a graphic - to get rid of the jaggies!

(I'm starting to think you're pulling my leg here....?)

[Ron Evans]

Both scanned fields are present to some extent so Robert is partially correct. The interlaced TV system works by using a combination of phosphor decay and fooling our eyes into thinking that the whole picture is still there. By the time the next field is due to be drawn the phosphors should be decaying away. There is never really black lines between the just scanned lines ( maybe a very fine guard band that is never scanned) but they are not as bright as they were when they were just scanned. The rate of change is such that our eyes/brain fill this in for us. Its not real. A still would not show what we think we see. The fields are overwriten so points that were bright last time remain bright etc. Those that are now not scanned decay to black. If the decay is too long we would never see black. So the decay of the phosphors is designed to just last until the next scan, or at least close. Since it takes time to scan the screen one can see that the whole screen is at different levels of decay at any time since the moment the electron beam has scanned the phosphor it is in decay. IT is thus neccessary to bring the scan rate to a maximum technology can manage ( not very much when the system was designed 50hz or 60hz) to help our eyes/brain create the illusion. The smoothness of interlace depends on this system of using our brain/eyes. Our brain fills in the missing pieces of information. IF we move to a true progressive system we must now capture the original in a way that meets these needs for a display technology that doesn't use this method to create the illusion. A true progressive display turns the whole screen on frame at a time. For this to display smooth motion as we perceive from interlace video we need to be above the flicker rate for our eyes/brain ( 60hz ). Anything shot at less than 60frames will not appear to have the smoothness of interlace. No movement the image will be sharp and clear, movement and it will stutter like 24p if it is displayed at a higher refresh rate than it was shot at. For me I will take the interlace system until we can have full 60 frames per second originals. There are lots of things wrong with our systems. Broadcast TV clinging on to the interlace system but just as bad is the film community clinging on to 24p. Both were created as compromises in technology many years ago and neither is necessary now. We don't have to have the jaggies of interlace and we don't have to have the stutter of 24p.

Can't wait for true progressive above the eye/brain flicker rate. Something like 1080p60.

Ron Evans