User profile for user: Brendan Jones
Brendan Jones Author
User level: Level 2
233 points

How to convert fields to frames? (and double the frame rate!)

Instead of deinterlacing interlaced material the usual way (field blending or motion interpolation) I want to get higher quality output by converting each field into a frame, thereby doubling the frame rate and losing none of the original motion information, i.e. PAL 25 fps interlaced would become 50 fps progressive (and similar for NTSC - 29.97 interlaced becomes 59.94 progressive).


This would require each field to be vertically stretched to make it a frame (simple to do with bicubic resizing) and alternate fields offset by 1 line to ensure spatial alignment.


But when I try to do this in Compressor it doesn't work. If I set the output frame rate to be 50fps (using PAL 25 fps interlaced material), set field order to progressive, and leave retiming controls at default, all that happens is each frame is deinterlaced first (Noooooo!!) then duplicated to double the frame rate. This is not what I want!!


Is there any way to do this in Compressor? What settings do I need to use?


The weird thing is I've got it to do the reverse successfully - take 50 fps progressive material, and turn it into 25 fps interlaced.

Mac Pro, OS X El Capitan (10.11.2), 3.2 GHz Quad-Core Intel Xeon

Posted on Mar 11, 2017 3:34 AM

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9 replies
User profile for user: Xygen75
Xygen75
User level: Level 1
4 points

Dec 18, 2017 7:19 PM in response to Brendan Jones

Hi Brendan,

AFAIK theres no way to deinterlace with compressor or FCPX.

I used JES Deinterlacer (https://www.macupdate.com/app/mac/13069/jes-deinterlacer) on my raw wedding video to deinterlace from 25i to 50p. JES will add the missing lines by interpolation.

I saved the outcome to a ProRes file, which I've then edited with FCPX.


Good luck,

Xy


P.S.: Sorry, I didn't read the whole thread and didn't realize that you already found a solution. Are you going to provide the plugin for download?

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User profile for user: bikervic
bikervic
User level: Level 1
4 points

Dec 18, 2017 2:58 PM in response to Duchy777

Brendan, I do a lot of analysis of athletes and require slow motion video to get finer resolution of spatial movement. However, most of my clients send in standard 30i clips. I find that the Vegas 15 video editor can slow down the video, but the way they replicate the fields is such that only field 1 is replicated and stretched into 1 usable un-blurred frame. Field 2 is lost as it is not replicated and stretched, so I lose 1/2 the motion/spatial resolution; the important thing is that they do generate 1 un-blurred frame that can then be replicated into a FREEZE frame for analysis. Of course the manual processing of each video frame in order to show un-blurred slow motion video is out of the question!

The approach that Vegas takes is quite poor and almost useless, but I applaud you for realizing the problem and in fact coming up with what looks like a product that I would purchase.

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User profile for user: Brendan Jones
Brendan Jones Author
User level: Level 2
233 points

Mar 25, 2017 11:22 PM in response to BenB

Looks like you edited or deleted your original reply, presumably because you realised you were wrong.


I understand exactly what a field is, and I've now written my FCP plugin as proof it is possible to do what I said (By the way FCP can display fields. You have to have magnification at exactly 100%, otherwise it just shows the lower field as the frame).


Here's the original interlaced frame. You may not be able to see the scan lines if Apple resizes the uploaded image (it should be 768 x 576 pixels):

User uploaded file

Here's the upper field (presented first). You can see it looks like a half-height frame:

User uploaded file

Here's the lower field (presented second):

User uploaded file

Here's the upper field stretched vertically to make a full size frame:

User uploaded file

And here's the lower field stretched vertically to make a full size frame:

User uploaded file

Do this process, and you convert 25 fps interlaced to 50 fps progressive without losing any motion information in the original interlaced stream. Ditto for NTSC 29.97 fps interlaced.


See, I told you it is possible, and it wasn't that hard to write the code to do it. A couple of hours.

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User profile for user: BenB
BenB
User level: Level 6
13,222 points

Mar 19, 2017 8:39 AM in response to Brendan Jones

Fields to not directly translate into frames. A "field" in broadcast is every other scan line of an image. I.E. only have the image. Two "fields" flash quickly on screen one after the other to create the illusion of a frame. Technically, two "fields" can combine to create one full "frame". A "frame" being the full image flashed on the screen quickly.


Interlaced video uses fields, progressive video uses frames. Converting 60i to progressive video properly yields 30p.


You can't make a whole interlaced field into a frame without having to "fake" half of the image, thus resulting in LOWER image quality. You MUST deinterlace video first in order to retime it, that's just physics. If you could achieve what you're trying to, you'd end up with much lower image quality.


2 fields = 1 frame, period, that's it. Sorry.

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User profile for user: Brendan Jones
Brendan Jones Author
User level: Level 2
233 points

Mar 24, 2017 12:12 AM in response to BenB

Thanks BenB for your reply but I have to respectfully and completely disagree.


A field is a half-height frame, e.g a PAL digital interlaced frame is 720 x 576 pixels in size, the fields it contains are both 720 x 288 pixels, interleaved with each other line by line. But these fields can be viewed individually (Final Cut Pro can do it), and they look like vertically squashed images. Therefore it is possible to simply "stretch" them out vertically to make a 720 x 576 pixel frame, either by duplicating each line, or (better) to use bicubic image resizing (like what Photoshop uses to resize images).


Capture each field, stretch each one out to full height, and voila - you now have twice as many frames and no interlacing if presented progressively.


The resultant video quality would be much higher not much lower. That is because the eye is much more sensitive to temporal resolution than spatial in a movie. Doubling the frame rate will make the motion look much smoother and much better than traditional deinterlacing. And bicubic image resizing is very good - the horizontal resolution doesn't change, and the vertical interpolation to stretch each field would be barely noticeable.


Maybe I should write myself some software to prove to you that far from being impossible, what I suggest is totally possible and would yield excellent results. It's what Compressor should be able to do but apparently doesn't

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How to convert fields to frames? (and double the frame rate!)

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