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Progressive Scanning Explained

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#1
Please note: The following is for NTSC playback but does apply to PAL also. For PAL, change the 480i/480p to 576i/576p.

This is taken largely from Panasonic:

Progressive Scan vs Interlaced

Progressive scanning, otherwise known as 480P (p=progressive), creates a picture signal with double the scan lines of a conventional interlaced picture, 480I (I=interlaced), to create a noticeably sharper image. The 480P image offers higher picture resolution and eliminates virtually all motion artifacts. Even on large screens, the progressive scan lines are barely noticeable and picture flickering is greatly reduced, so you can enjoy extended viewing without eye fatigue. There are also many advantages to progressive conversion.

The Benefits of Progressive Vs. Interlaced Scanning
Standard DVD-Video players use interlaced scanning to produce a picture. Interlaced scanning combines two fields to generate a picture of 525 scan lines (480 of which are displayed). Your television projects an interlaced image by first scanning the 240 odd-numbered lines of one field (in 1/60th of a second), followed by the 240 even-numbered lines of the other field (in 1/60th of a second). So, it takes two fields to build one frame of video.

Progressive-scan DVD players have a progressive video processor, which enables all 525 lines (480 of which are displayed) to be scanned at the exact same time. A television with 480P component inputs can completely scan the entire image in 1/60th of a second, so it only takes one field to build one frame of video. The result is a smoother and sharper picture, with high resolution and no motion artifacts.



Films are normally shot at a frame rate of 24 frames per second. This is also the rate used to transfer the vast majority of films to DVD-Video. In other words, DVD-Video movies are usually recorded as 24-frame progressive scan images. So what happens when they are reproduced as an interlaced image? To match the TV field rate of 60 fields per second, each of the film's 24 frames must be shown either twice or three times in an alternating sequence. This kind of conversion sometimes causes two different film frames to overlap as they make up one TV frame, causing visible jaggedness along contours in the picture.


Converting film's 24 fps rate to video's 30 fps rate.
Conventional interlaced video results in "frame mixing" which can cause motion artifacts.

With progressive scanning, this kind of frame overlap doesn't occur. To match the TV field rate of 60 fields per second, it's still necessary to scan each film frame two or three times, as in interlaced scanning. But this is followed by a pattern detection algorithm, that determines which fields should be paired to reassemble the frames as they were on film. This process, called inverse 3:2 pull-down, results in a series of complete de-interlaced frames.


Inverse 3:2 pull down

When the video shows a still image, the common way of converting it to progressive-scan is to combine two fields. When the video shows motion, the common way is to interpolate the missing data between lines. However, the resulting difference between still and motion images is readily apparent on a large screen. This method also tends to misinterpret slow movement as still images, thereby causing jagged edges on moving objects.

Instead, progressive-scan DVD players compute the missing scan lines based on multiple line data from at least two fields. This VT processing method employs the same algorithm whether there is motion or not, so quality is consistently good and misdetection is not an issue. The result is natural image reproduction for large-screen viewing.

Advantages of Progressive Conversion

Line doublers are used in other high-end home entertainment systems to provide progressive scanning. These may be stand-alone devices or incorporated into a digital TV. Impressive as they may be, progressive-scan DVD players' in-player progressive conversion has three big advantages over line doublers:

1) High precision and stability
A DVD-Video disc mastered from a film holds all the data necessary to produce an accurate progressive image, whereas an external line doubler must take hints from the video source to determine the source material and frame allocation.

2) All-digital conversion minimizes signal degradation
Since the signal from the DVD-Video disc is digital, progressive conversion can be performed digitally inside the player. Signal quality is protected until it leaves the player's analog output. In contrast, a stand-alone or in-TV doubler first receives information from the analog output of the source device then converts this analog signal back to digital for processing. Finally, it must translate the signal back to analog before outputting it. All this back-and-forth translation is much more likely to degrade the signal.

3) Processing is optimized to DVD-Video's high image quality
Line doublers built into digital TV sets are designed to work with a variety of video sources, so their settings are not necessarily ideal for DVD-Video. The progressive conversion of progressive-scan DVD players is optimized for the high resolution and low noise of the DVD-Video format. This enables the unit to preserve DVD-Video picture quality for display on all screen sizes, from direct-view CRT to projectors.
This message has been edited since its posting. Latest edit was made on 04 Mar 2004 @ 7:09

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#2
hiloguy Suspended due non-functional email address
This may seem like a dumb question, but here goes anyway: Is it safe to assume that a RPTV (Mitsubishi WS55313) that shows "480P" in its video features specs will actually be set up to accept Progressive scan info from a ps dvd player? I would like to buy this TV, but this model doesn't show anything about "progressive scan" in the Mits ads, while their more expensive models specifically state "Progressive scan." I've also seen this model listed on various Web sites with the notation, "progressive scan: no."

The dealer says "yes."

HELP!

Thank you!

beachbum
#3
There are two types of picture and that number of lines. 480i (interlaced) and 480p (progressive). If the TV shows that it accepts 480p as a signal, then it definitely is a Progressive scan compatible TV. What the specs prob mean is that the TV doesnt have a Progressive scanning unit on board, but that it will accept a Progressive scan signal. This means that if you buy this TV, your DVD player will need to be able to output a Progressive scan signal (note tha Progressive scanning is different on DVD players for PAL and NTSC).

Hope this helps
Chris

#4
hiloguy Suspended due non-functional email address
Thanks for the reply! Yes, your answer (plus your excellent description of "progressive scan") did the trick. I'll buy the RPTV immediately!

I LOVE this forum!



beachbum
#5
No problem, glad i could help. Happy viewing on the RPTV ;-)

Chris

#6
alseides Suspended due non-functional email address
i started a separate thread on this, but it might apply to this thread as well since it concerns dvd resolution.

some players support an upconversion to 720p and 1080i. i have a 1080 capable tv that has s-video and component. how does upconversion and how will it affect my picture? (i have a 57" wide HD sony)

#7
The resolution upconversion does, will not actually add any real picture information to the image, as you cannot create real picture information where none existed before. What upconversion theoretically does is create a smoother look for non-HDTV signals. Upconversion, which is also known as line doubling, reduces the visibility of horizontal scan lines, which become more noticeable on screens larger than 32". With my 60" screen, and no doubt your 57" screeen, upconversion (line-doubling)will make the lines on the screen less noticeable.

Similar in fact to what Progressive scanning does, except that it of course, changes it from an interlaced signal to a Progressive scanning signal, but the principles are the same - smoother images on screen.

Hope this helps
Chris

#8
hi:
I guess this reply is directed to Oriphus. I was in the Bose outlet and the salesman there who seemed to be very knowlegeable gave me this explaination for Progressive scanning. I brought the subject up because the Bose Lifestyle dvd players are not Progressive scan. he said that as long as your TV is Progressive scan that the dvd player does not have to be to get true Progressive scanning. I have a Panasonic Tau (circa 2000) flatscreen crt that is NOT HD but does have 1 set of component inputs. So do you think if I use an interlaced dvd player on this set I am getting Progressive scanning? Thanks...

PennsylvaniaRon
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#9
I have question on Progressive scanning.

While playing a dvd, on one of the on-screen menu's on my dvd player (Harmon Kardon DVD25) the disc type either shows interlaced or Progressive.

So it would appear that some movies are encoded Progressive, while others are interlaced. Does this mean that to benefit from Progressive scanning (even if you have all the right hardware), it's still dependent on the encoding of the movie?
#10
Hi Guys, Ill answer PennRon first.

PennRon: The guy in the Bose store seems to be incorrect. Take a TV and connect a Progressive scan DVD player in Progressive scan mode and connect it to a TV that does not support Progressive scanning, you will get no picture. I have a similar Panasonic Television which is only interlaced. If your TV did support Progressive scan, you still need a device to convert the moving images from interlaced to Progressive, and thats were the DVD player comes into the picture.

What can happen though, is that some TV's have a Progressive scanning unit built in (very different to supporting P-Scan) which will take a signal and convert it to Progressive. However, I dont believe your TV does this, most dont. Basically, if the player doesnt have the built in P-Scan then you wont be able to get a P-Scan image.

To answer you question, i dont think you are going to be getting a Progressive scan image since i dont think your TV has a P-Scan converter, merely support for a P-Scan signal....



garym - NO, DVD's are not encoded as Progressive scan or as interlaced. They merely have a number of MB/s of data that is sent to a TV via a DVD player. (THis is my understanding of it). As long as you have a P-Scan player and a compatible viewing source (TV, Projector, etc) then you will be able to view your DVD's in Progressive Scan mode at XXXp that uyour system supports

Thanks
Chris

#11
chris: I'm not sure that's the case, let me explain better...

I have connected my Progressive scan player by component to my plasma.

While playing a disc, if I bring up the disc info screen, there are two pieces of information on here.

1) 'Output scan type', this always says 'progressive'
2) 'Movie scan type', this sometimes says 'interlaced' and sometimes says 'progressive' - it varies from disc to disc - this seems to indicate that the discs themselves are indeed encoded differently in some way?

Any ideas?
#12
Well, im honestly not sure - I will try to find out though. Everything i have plays P-Scan at all times. I'll get back soon with an answer....

#13
Hi, it was as i said it is. DVD video is encoded in mpeg2 format at a certain amount of frames per second, depending on the format its encoded in (NTSC or PAL). Its read at a certain bitrate on hows it encoded.

#14
thanks for the info
#15
Hi, No problem Gary. Check your user manual to see what it gives as the reason for the information it provides...

#16
aren't Playstation 2 consoles Progressive?
#17
Some may support it, but i really dont know. PS2's arent really one of my areas of expertise im afraid :D

#18
yes the ps2 is, I've hooked mine up to my plasma with a component cable, and played MTX motocross - in the options in the game you can choose either 480i or 480p (progressive).

It looked very good.
#19
Hi Gary, just on the Progressive Scanning issue, i've just found out that some DVD's have flags built in that better allow the DVD players to rebuild the Progressive scanning image. this may be what ur experienceing

#20
Oh right, how does that work then?

btw I looked in the manual, it says "... pressing the disc info button will display information about the disc..."

Very informative!
#21
alseides Suspended due non-functional email address
Just thought I would add to the PS2 post. The newly (well, kinda new) released version of the PS2 v50000 has some new features:

Added Progressive Scan video out
New DVD Player firmware 3.0
New Remote Control support: Power on/off and tray open/close button
30% more silent compared to older models
Support of DVD-R/RW/+R/+RW media

What you are probably intersted in the the p-scan output. I think that previous models did not support pscan. But this one does.

#22
The flaggin system is quite simple. A set of structured commands that a DVD player picks up on. Why its needed i have no idea and the technical aspect of what it does i have no idea, but apparently it does exist and thats as much as i know ;-)

Chris

#23
Since DVD is designed to be viewable on an interlaced TV, the video has to be stored in that format. Depending on the source, however, it's sometimes possible to use something called pulldown to convert progressive to interlaced without changing the original stream. The most common (at least in NTSC land) is 3:2 (AKA 2:3) pulldown. You'll also see this referred to as telecined and the process of deinterlacing it as inverse telecine (or IVTC). This involves adding flags to a 23.976p video stream to make it read as a 59.94i (AKA 29.97i) stream. The video still has it's original information, but when it's read by the player, 4 frames become 10 fields (5 frames).

Let's say you're looking at 4 (23.976p) frames from your original stream (we'll call them F1, F2, F3, F4). The interlaced stream that's actually read looks like this:

| F1 | F1 | F2 | F3 | F4 | Field 1

| F1 | F2 | F3 | F3 | F4 | Field 2

Notice that all then information is still there, so a deinterlacer can theoretically recover the progressive frames.

There are also different ways to deinterlace 3:2 pulldown material. Some deinterlacers only read flags. Unfortunately, since not all film material is actually telecined (some is actually encoded at 59.94i in the telecine pattern), just following flags won't always work. Another method is to just compare fields for matches to find the pulldown pattern. If it's a close enough match, the deinterlacer will then recover the progressive frames based on that. This gets particularly tricky when you deal with a lot of TV material, since it's common to have the original footage shot on film and any effects, titles, etc., ... done in video. That gives you a hybrid stream that has both telecined film and NTSC video parts. Since real interlacing has different requirements for deinterlacing than telecined film does, that can cause the video to not display correctly, particularly during transitions between the film and video. Then it can get really ugly when a hybrid source is transferred to PAL, but that's another issue (and beyond me to explain in a way anyone could understand it).

The other type of pulldown (that I'm aware of anyway) is 2:2 pulldown. Like 3:2 pulldown, the name denotes a pattern of fields. For 3:2 pulldown it's an alternating pattern of 3 fields from one progressive frame followed by 2 from the next progressive frame. In the case of 2:2 pulldown it's 2 fields from the first frame followed by 2 from the second. Basically that just means it's actually progressive, but since it already displays at the same fps as the video format being used, it can just be split into fields and displayed as is. That also means that when you want to deinterlace it you can just put the fields back together without having to do any fancy calculations.

I've never seen any 2:2 pulldown, but I believe it's more of a PAL thing. Basically, if you speed up a film to 25p (instead of slowing it down to 23.976p like in NTSC) you can turn it into interlaced content without doing anything. Obviously 2:2 pulldown doesn't actually require any flags, since the video would look exactly the same with or without them.

Edit: I just noticed that a lot of the pulldown information was in the original post. Maybe if I'd re-read it I'd have saved 15 minutes of typing.
This message has been edited since its posting. Latest edit was made on 01 May 2004 @ 8:16

Rich Fiscus
@Vurbal on Twitter
AfterDawn Staff Writer
#24
lol - indeed, Pull-down has been explained, but the flagging information was very informative Vurbal, cheers ;-)

#25
No problem. Always happy to show off... err uh help.

Rich Fiscus
@Vurbal on Twitter
AfterDawn Staff Writer
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