Progressive Scan vs. Line Doubling (1 Viewer)

[Bart]

Hey guys,

Can you tell me the difference between progressive scan and line doubling? I saw an amazing TV a few weeks ago (36" Sony Wega XBR) and the guy who owned it said it looks great because he is using component video inputs and a progressive scan DVD player. A friend at work said that progressive scanning should only affect the refresh rate, not the resolution. He said the reason the TV looks so good is because of the built-in line doubler. I thought progressive scan WAS line doubling. Can someone please explain the difference for me? (if there is any). Thanks.

Bart

 

[Mary M S]

I would like to see the answer to this one. Was going to start shopping for a prog. scan DVD for an upgrade after purchasing a LCD Sony GW.
But the Sony has no refresh rate, so if Prog DVD is all about refresh rate....?

 

[jeff lam]

My understanding is that they are the same thing but usually the progressive signal from the DVD player (even a cheap one) will outdo the line doubler on most TV's. So, in other words, if your TV's line doubler is better than your progressive output on your progressive player, you just wasted your money on the player because you can't use both. Usually this is not the case though as I guess even the cheap progressive players do a better job than most TV's. I too am curious as to what the experts say on this one.

 

[John Royster]

I'm no expert on video but here's my take on it.

Progressive scanning in DVD world means taking the interlaced fields on the DVD and combining them into a whole frame. This is done digitally so "most times" it is better then any line double in the TV. Very similar to line doubling if not the same.

Line Doubling - taking an interlaced source to display a progressive picture. Combines two interlaced fields to display a single frame. Almost identical to DVD world except being done on an analog signal.

And your friend is WAY off base here. When fed a progressive signal a TVs internal line-doubler is completely bypassed. How you gonna convert fields to frames if the progressive signal already contains frames?

 

[Michael Reuben]

They're effectively the same thing, since both generate a 480p signal.
In common parlance, "progressive scan" generally refers to a DVD player capable of generating a 480p output, while line doubling refers to external circuitry (either inside a TV or in a separate unit) that works on the signal after it leaves the DVD player.
Obviously, one advantage of line doublers is that they can be used for signals other than DVD. The advantage of p/s players is the fact that their operations are performed entirely in the digital domain, and the player can take advantage of "flags" imbedded in the datastream to do the reverse 3-2 pulldown accurately (assuming the flags are accurate, which isn't always the case).

A friend at work said that progressive scanning should only affect the refresh rate, not the resolution.

The same is true of line doublers. There are also scalers that can upconvert an image to a higher apparent resolution, although it's largely an illusion. Perhaps that's what your friend was thinking of, since some TVs do upconvert their input to something greater than 480p.
M.

 

[Allan Jayne]

In a sense making progressive scan out of interlaced video is always a form of line doubling, we end up with twice as many scan lines per second as there were before.
Plain line doubling consists of outputting every scan line twice. This does mean that we output each scan line in half the time it originally took. If we started out with interlaced video the result is progressive scan, although we get a better picture from de-interlacers that do more than simply output every scan line twice.
By "do more" we mean do such things as take portions of scan lines from the next or previous field if the material fits better than interpolating what should go in between a pair of odd scan lines or a pair of even scan lines. It so happens that if the subject matter is stationary, taking material from the next or previous field is better, while when the subject is in motion, interpolating is better. Weaving together the entireties of two consecutive fields to get a progressive scan video frame is also done, but is not always the best thing to do. The 3-2 pulldown (repeat pattern) of film source video means that there are consecutive frames that are "stationary enough" to permit weaving their entireties without artifacts. Nevertheless the best DVD players doublers spot check the content to be sure that pairs of fields flagged as being the same really are.
All line doublers used in today's consumer video equipment are digital, which requires that each scan line be broken up into pixels which may or may not correspond with pixels the video may have had earlier in its lifetime. Horizontal resolution is lost if the doubler does not chop up the video into small enough pixels, or if the new pixels do not line up with a pre-existing pixel pattern (pixel footprint). When the video going into the doubler is already in digital form (does not include coming down a component video cable) and the doubler works with the same pixels (pixel for pixel) there is no resolution loss. This is where the DVD player with built in doubler has its advantage over doing the doubling in the TV or in a stand alone unit.
Video hints:
http://members.aol.com/ajaynejr/viddoubl.htm