progressive and interlaced

Artistic Support Compositing and Post Processing
1

Can someone help me with this one:
In thBlender I’m told for TV I must render in fields i.e two images per frame, or interlaced, to get a clear picture. If not the image will appear blurry on a TV screen. And I should render single frame for computer presentation.

Now HD camera’s (ex 3 for example) are shooting progressive (am I right on that one?). Firstly why is the image clear on a TV screen if its progressive rather than interlaced? And second, if I want to mix live action with animation, should I render my HD 3D footage progressive rather than interlaced? Can anyone clear this up for me?

2

Only time interlacing is dictated is for broadcast.

And I should render single frame for computer presentation.
Not necessarily but generally. If your source is already interlaced, ie video file and you’re just editing without many effects or compositing and you are going to DVD then it’s possible to stay interlaced. DVD can and is commonly interlaced and media player software on a PC will generally handle interlaced by deinterlacing. But deinterlacing will generally mean loosing half your vertical resolution.

Now HD camera’s (ex 3 for example) are shooting progressive (am I right on that one?). Firstly why is the image clear on a TV screen if its progressive rather than interlaced?
Many newer cams shoot true progressive, (as well as interlaced) some shoot pfs which is interlaced but the two segments are frames with no time difference.

You need to make sure your editting software knows what it is it’s dealing with and also with regard to interlaced the field order. Things will go wrong with editing, effects and playback otherwise.

And if there are things like colour space conversion going on in your NLE from YCrCb/YV12 to RGB it’s important that the software knows it’s interlaced. Otherwise you’ll be loosing quality in the conversion, it’s a lossy conversion already.

And second, if I want to mix live action with animation, should I render my HD 3D footage progressive rather than interlaced? Can anyone clear this up for me?
Depends on purpose, if you want to undercrank or overcrank and your vid cam doesn’t offer that in cam then shooting a section of your video interlaced and then deinterlacing and slowing the video down is far smoother and cleaner than just applying a slow down on progressive.

Progressive for everything else. If you intend using blender for this editing. Nodes doesn’t handle interlaced very well I believe, blender is designed for progressive editing. The VSE is more standalone and can handle interlaced I think.

3

Thanks yellow for getting back to me. Still confused though. Can’t get my head around it!

Ok I’m gonna be shooting live action footage and doing the vfx in blender. I’ll be editing on premier and AE. Premier gives the option of 1080i and 1080p. The live action will be shot HD on the ex3 more than likely.

I’ll presume I should choose the 1080p option? Should I render from blender using fields if the editing option is progressive? If I don’t will premier interlace everthing for dvd?

4

if you’re mixing it with something else (IE camera footage) match that.

If it’s blender alone then render whatever you would want (normally progressive). If it’s for DVD alone I’d suggest rendering 24fps progressive 720x480 (if you’re in USA/Canada), that’s allowed in the DVD spec. If you’re mixing with other footage again, match that (in USA/Canada DV = 720x480 interlaced 29.97fps progressive, HDV = 1440x1080 interlaced 29.97fps)

5

Sounds like you have the option to go Progressive the whole way. If so I’d just do that.

Basically progressive scan has a more, well, “film-like” look if you will. That was originally what all of the hype was about 10 years ago or so - gee, has it been that long? That was about when it started to hit the market more broadly in cameras, though I am sure it had been around a lot longer.

One of the main advantages of 24p is you can take film footage and transfer it over and remain more true to a projected look. That is because each frame is scanned once (similar to a camera and projector) rather than two times (interlaced).

The interlaced look is what has been associated with TV footage. A more “video - like” look.

Personally, I have always been able to tell the difference between the two even when shown on an NTSC interlaced monitor. I have also had the great opportunity to see the film I shot (that we edited in Progressive) projected at the Archlight Cinerama dome. The consensus was that we had transferred to film, when in fact it was just a very good video projector projecting the progressive tape in Progressive on the screen.

As noted above there are some technical issues to consider. However for the most part, I think you’ll like the end result better if you shoot in 1080p and then render in progressive.

Just make sure in Premier, to see to it that each clip is set to Progressive, (not sure how Premier does this, just check them to make sure is all I am saying) and the project is also set to Progressive. And when you render out any composites or final edits from Premier you select Progressive. Same would be true I expect with AE. Sorry I use Vegas. But the basic idea is still true. Make sure all your settings are progressive as you go down the pipeline - including the MPeg files you render for the DVD output.

If you change your mind later you can always convert clips to interlace. NLEs are pretty good with this stuff these days, so there should not be any problems.

As a technical note: I had done quite a bit of experiments before shooting. And in the end I shot in interlaced but when I did the editing, I converted the clips to Progressive. But that was an old camera. These days you can just shoot progressive with most real nice cameras that have true progressive. But it is a good idea to do tests before you get to the set and see what works best in your situation.

The bottom line is you always have options to convert in post. You should shoot based on what looks best or works best in tests you do beforehand.

6

The project is for broadcast purposes. What do you mean match it? if I shoot progressive then the rendering should be progressive? Does the editing software then interlace the footage? |Does it need to be interlaced?

7

:RocknRoll:

if I shoot progressive then the rendering should be progressive?

YES! if it’s for broadcast then you should pick some HD broadcast format as the final render format. IE 480p, 720p, 1080i/p. But if you’re mixing your 3D (ie special effects, etc) with video footage, match the video footage. You’ll get less issues that way.

8

What you really need to do first is check what the actual broadcast delivery requirements are in the target area of distribution. In different parts of the world this is likely to be different.

wiki:

HDTV broadcast systems are identified with three major parameters:

  • Frame size in pixels is defined as number of horizontal pixels × number of vertical pixels, for example 1280 × 720 or 1920 × 1080. Often the number of horizontal pixels is implied from context and is omitted.
  • Scanning system is identified with the letter P for progressive scanning or I for interlaced scanning.
  • Frame rate is identified as number of video frames per second. For interlaced systems an alternative form of specifying number of fields per second is often used.

I am pretty sure that how this is implemented is different in various parts of the world. And some places don’t even have HD yet. And some may support p and some only i.

So if you don’t know already or the client does not know, Google it or call a broadcaster in your area for a link to a website.

I would get that settled first. I have not kept up with it lately and I can’t seem to find links now that tell exactly what the current formats are.

Just know that there is a difference between broadcast standard and what part of this is actually adopted in a particular region/network etc.

As an example from NBC website FAQ:

Aren’t there two different HDTV formats (720p and the 1080i)? Which will a new HDTV receive?
The Digital Television (DTV) standard allows broadcasters to choose among several different formats that they can transmit. There are two high definition formats: 720p and 1080i. NBC broadcasts HDTV in the 1080i format, which provides the highest possible resolution to our audience. But you don’t have to worry - any HDTV receiver will receive both formats.

9

Your production pipeline can be ALL progressive, it gets displayed with interlace if necasary at the end. If you have seen a film on TV then you have seen this workflow.

The editing package just wants a setting to work with so that all elements of media you use (interlace or progressive), become just one type at the end. Broadcasters want a uniform deliverable.

Interlace = smoother pics (over time)
Progressive = sharper pics (per frame)

10

Precisely what it took me many more words to say. lol.

But agreed. This is the idea. NLE are designed to support this workflow so you can deliver in multiple formats if necessary.

For my film, I used a deck that could record in i and p and I delivered two versions to the distributor. One for DVD p and one for broadcast i.

(By the way I never understood why they insisted on a tape for the DVD delivery. Hopefully that kind of stupidity is starting fall away by now. That was way back in olden times - circa 2004. I could have just handed them a digital version on a DVD data disc ready for DVD authoring. But nope. Had to be a tape. Go figure.)

11

R Culver, maybe they (thought they) had a better compressor and wanted to start with best quality master? Ya cant garuantee what other people give ya, unless its a tape, the manufacturer garuantees that as standard at least.

12

Come to think of it, that - considering I’d deliver an mpeg - would be a factor. However I offered to give them the digital file - the original not the mpeg and they could do what they wanted. reflecting on it now, I think it more has to do with standards set not by them but by the buyers - expecialy in other countries. Digital media had not hit everywhere just yet back then. In fact here in Thailand where they manufacture the hard drives I buy in the US, they are still broadasting SD for TV and using old sony cameras to record live shows.

13

I think the the EX3 has 35mb/s 1920x1080p HQ mode (For PAL 50i/25P, Ireland?) and 25mb/s 1080i 50i / 25P(psf) (HDV 1440x1080 compatible) SP mode.

I’ll presume I should choose the 1080p option?
If you shoot HQ yes. If you shoot SP then a HDV 1440x1080i with and state no deinterlacing (as the source will be psf I think) may be a better option. In AE you can set your preview to 1920x1080 but work with a 1440x1080 time line.

You really only want to scale your video once in the workflow, so do 1920x1080 or 720p etc at the delivery end, not before editing and then again at delivery, hence 1440x1080 for SP mode.

Composite blender renders (32bit exr image sequences) + video exported from premiere (full range RGB) as tif image sequences (for your comps at least), into a 32bit linear environment in AE. Suggest not using Premiere for anything other than the edit / slap composites as it’s still 8bit?

Should I render from blender using fields if the editing option is progressive? If I don’t will premier interlace everthing for dvd?
No interlaced out of blender.

14

tape’s less compressed then a DVD, that’s most liketly why they wanted a tape (betting they encoded to their own system).

Get ahold of the local station you’re giving it to, they can give you specs (delivery format will be more important). Hopefully it’s a local, they normally have much more lax requirements. IE NBC says it does 1080i, but local stations most likely still take SD stuff. I’ve noticed CBS has bad black artifacts & all of ABC’s national commercials sound tinny in Digital. :slight_smile:

15

Thanks everyone for the replies. So I’m ignoring what the blender wiki says about rendering for TV (I presume its out of date) and just render one image per frame from now on…

I have been working on a short film and its been interlaced all the way but from now on its all progressive on other projects. The only reason i was interlacing was that it would be suitable for broadcast - but now no need. Cheers guys

16

Be aware of (the need for) motion blur however, as progressive frames (low temporal sample rate) can look somewhat strobe-y. Traditional interlace video is sampled at least double that sample rate making motion smoother.