Who does deinterlace?

[John Rofrano]

[fabio mereghetti] “Put it on a Vegas timeline and applied Mercalli v1.1 to deshake it: “

is it still interlaced or Mercalli output is forced progressive?

It is still interlaced. Mercalli may deinterlace to process the motion but that motion compensation is then applied to your interlaced footage.

Does it depend on how I will encode at render time?

Yes, if you want to deinterlace, render time would be one good place to do it.

What effect does project property “deinterlace method” has on the process?

This tells Vegas what method to use when it need to deinterlace the footage. This is what it will use when you render to progressive, or if you use a plug-in that requires the video to be progressive in order to process it. If Vegas never needs to deinterlace your footage this property is not used.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Hallgeir Gjesdal]

What is Deinterlacing? Facts, solutions, examples —> https://www.100fps.com

[Fabio Mereghetti]

Thanks.

@Hallgeir
Yes, I know what interlacing is but, for me, sometimes it’s not so clear who-does-what in a workflow chain where a clip is dealt with NLEs, plugins, AVS script with commands and functions and software or hardware players to whatch the end result.
As you surely know a “not mentioned” deinterlacing can take place at any of the steps above. I think that if you don’t care about it you could even end up with applying more than one deinterlacing process to you clip with the consequent degradation in quality.
As John and all the learned guys here and elsewhere are never tired to repeat, from an interlaced source, the best quality you can get is to keep it interlaced from the camera till your (or your clients’) PAL DVD player will send it to that amazing TV set they’ve just bought! Or am I wrong?

@John

Well, I did some homework about this subject and this is the workout, for the moment:

Source (resting on a Vegas 9e pro timeline) = m2t 1440×1080 50i
Project settings = HDV 1440×1080 50i PAR1.3333

I did six different renders, all of them frameserved with Debugmode to an AVS script (with just avisource(“..”)), opened with Virtualdub and saved from there to AVI uncompressed with no Vdub filters. (I did this to have an easy preview of at least the first frame)
Then, with another AVS script I put them six together (cropped) for easy comparison. Here is a screenshot of Vdub:

The caption has this meaning:
mercalli[no/on] + prj settings field order[upper field first/none] + Prj deinterlace method[interpolated/none]

I’m doing all this not just for learning – even if I find it very interesting, but because I want to make some slow motion through AVS MVtools 2 and, thanks to a well explained script of John Meyer, I’ve been able to get nice results.
In fact, this is true for the plain m2t files (the script can manage interlaced clips) but I’m getting bad output after applying mercalli. Unfortunately, being just an amateur, I’m dealing with hand shot clips that need deshaking and you have already hinted me to feed mercalli with the original speed clip instead of applying it after the MVTools interpolated frames are added.

The final rendering for “the public” (proud parents…) will have to be a DVD Widescreen (PAL land) but I would like to keep a higher quality original on my media center.

While I go back testing – this time with the JM script, to see the different results I can get from different sources and with different settings, I would be glad to listen to your comments about it. Thank you.

Fabio.

[John Rofrano]

I’m not sure where you are going with all this. The images look exactly as I would expect them to look. If you’d like an explanation perhaps this will help in understanding what’s going on.

Source: Interlaced footage Upper Field First (UFF)

A: Mercalli: Off, Project Filed Order: None, Deinterlace Method: Interpolate

Since the footage is interlaced and the project is progressive, and you told Vegas to deinterlace using Interpolate, it has thrown out half of your vertical resolution and use one field producing a very pleasing progressive image.

B: Mercalli: On, Project Filed Order: None, Deinterlace Method: Interpolate

Since the footage is interlaced and the project is progressive, and you told Vegas to deinterlace using Interpolate, it has thrown out half of your vertical resolution and use one field producing a very pleasing progressive image. Mercalli processed the video correctly because all of the settings were correct in your project.

C: Mercalli: Off, Project Filed Order: None, Deinterlace Method: None

Since the footage is interlaced and the project is progressive, and you told Vegas to deinterlace using none, it is not processing the fields and instead showing them to you giving you a very unpleasant “comb” effect that is indicative of incorrect field processing.

D: Mercalli: On, Project Filed Order: None, Deinterlace Method: None

Since the footage is interlaced and the project is progressive, and you told Vegas to deinterlace using none, it is not processing the fields and instead showing them to you giving you a very unpleasant “comb” effect that is indicative of incorrect field processing. Passing this garbage to Mercalli just leads to more garbage and Mercalli made the comb even worse.

E: Mercalli: Off, Project Filed Order: UFF, Deinterlace Method: None

Since the footage is interlaced and the project is interlaced, but you told Vegas to deinterlace using none, it is not processing the fields and instead showing them to you giving you a very unpleasant “comb” effect that is indicative of incorrect field processing.

F: Mercalli: On, Project Filed Order: UFF, Deinterlace Method: None

Since the footage is interlaced and the project is interlaced, but you told Vegas to deinterlace using none, it is not processing the fields and instead showing them to you giving you a very unpleasant “comb” effect that is indicative of incorrect field processing. Passing this garbage to Mercalli just leads to more garbage and Mercalli made the comb even worse.

So… what have we learned?

NEVER set Deinterlace to none if you have interlaced footage. 😉

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Fabio Mereghetti]

Thank you again for your time.
Unfortunately, I must be a little thick so let me ask you something more.

Lets say I load an HDV 50i m2t clip just for a color correction and then I want to render it to an uncompressed AVI ready to be used again or compressed outside Vegas: which are the project settings that will let me keep the best possible quality?

Reading around I thought it would be HDV 50i UFF with deinterlacing set to none (the “E” example above) but your comments

NEVER set Deinterlace to none if you have interlaced footage

seems to say that we always have to deinterlace, so now I’m more confused than before…

And about the “F”: didn’t you say that Mercalli is able to deal with interlaced sources?

So, why deinterlace?

[John Rofrano]

[fabio mereghetti] “seems to say that we always have to deinterlace, so now I’m more confused than before…”

I did NOT say that you HAVE to deinterlace. I said that IF your footage is interlaced you MUST tell Vegas what method to use if it NEEDS to deinterlace it for any reason. If you don’t you will wind up with a mess.

[fabio mereghetti] “And about the “F”: didn’t you say that Mercalli is able to deal with interlaced sources?”

Yes, but only if you set the deinterlace method properly. You told Mercalli that if it need to deinterlace the footage, that it should NOT. So it did not deinterlace it and you got a mess.

When I said that Mercalli handles interlaced footage properly I was not saying that it did not deinterlace it. I was saying that you don’t have to worry about deinterlacing it because Mercalli will take care of the for you. It probably does deinterlace the footage at some point to track the motion properly and then re-interlace it to conform to the media settings. In the case of ‘F’ it was not able to do that because deinterlace was turned off.

[fabio mereghetti] “So, why deinterlace?”

There are times when Vegas and plug-ins need to deinterlace the footage in order to process it correctly. If you turn off deinterlacing, it will not treat the footage correctly.

~jr

http://www.johnrofrano.com
http://www.vasst.com