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View Full Version : Why should deinterlacing be done after cropping?

orion44
15th July 2020, 23:27
http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-telecine.html

The above article states:

Also, deinterlacing should be done after cropping and before scaling.

Why should deinterlacing be done after cropping?

I always deinterlace first, and then crop and resize.

Will I mess up my encodes if I deinterlace before cropping?
manono
16th July 2020, 06:51
The guy says, "For interlaced (not telecined) video, you must always crop vertically by multiples of four...". If you don't, you'll royally screw up the video. Me, I'd rather deinterlace first. If deinterlacing is even called for.

He also claims, "Telecined video was originally filmed at 24000/1001, but was telecined before it was written to the DVD." so I'm not sure I'd believe all that he says.
orion44
24th July 2020, 23:30
The guy says, "For interlaced (not telecined) video, you must always crop vertically by multiples of four...". If you don't, you'll royally screw up the video. Me, I'd rather deinterlace first. If deinterlacing is even called for.


Why does interlaced video need to be cropped vertically by multiples of four?

After the video is deinterlaced, is it ok to crop vertically by multiples of two?
manono
25th July 2020, 06:44
Why does interlaced video need to be cropped vertically by multiples of four?

You can figure out the answer yourself by just reading on AviSynth's Crop (http://avisynth.nl/index.php/Crop) page.
After the video is deinterlaced, is it ok to crop vertically by multiples of two?
Same answer as before.
foxyshadis
1st August 2020, 11:24
http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-telecine.html

The above article states:

Also, deinterlacing should be done after cropping and before scaling.

Why should deinterlacing be done after cropping?

I always deinterlace first, and then crop and resize.

Will I mess up my encodes if I deinterlace before cropping?

Honestly, that line was written 20 years ago (https://web.archive.org/web/20040409040211/http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-telecine.html), when CPU power limits meant that deinterlacing unneeded pixels might mean the difference between 2 fps and 4 fps. (And if you go all-in on QTGMC, it can STILL be that way.) Documentation is the last thing to get worked over, so a lot of advice from the 90's and 00's is still floating around.
Katie Boundary
28th September 2020, 20:05
Solid black areas don't show visible scanlines even when interlaced, so they can screw up field-matching.