Cropping 4:3 down to 16:9 - horizontal jaggedness

TimmyRaa wrote on 11/12/2003, 6:07 AM
Continuing with my wedding video saga, of my two cameras that I had going, one was filming in widescreen (16:9) - my preferable choice - and the other was older and could only film in 4:3.

I'm sticking with widescreen for the final presentation, and just cropping the top and bottom off the 4:3 shots. However, I've rendered some of it to see how it looks, and the cropped 4:3 stuff looks terrible; I'm getting horizontal 'jaggedness' (my word!) down the edges of things, when there is motion. Looking at a still subject, the picture looks acceptable, but motion is terrible. There's a screen capture showing what I mean here - http://www.timspence.co.uk/weddingjerkyness.jpg.

I realise that when I crop the 4:3 picture, and then stretch it vertically to fit 16:9 aspect ratio, I'm losing some vertical detail, but it shouldn't look like that!

Can anyone help, or suggest better ways to do it?

Comments

farss wrote on 11/12/2003, 6:59 AM
They are normal interlace artifacts. Theyll look even worse if you've stretched things. But fear not, all will be well when you play it back on a TV.

OK, you think I'm nuts right!

Computer monitors only display video as progressive scan but your video is made of two fields taken at different points in time. One of those fields contains all the odd lines and the other one all the even lines. On a TV they are displayed one field, then the next field field filling in th lines missed in the first one. Work just great! Except you cannot really do that on a computer monitor, VV has no choice but to display the two fields at once so your eyes see what you see. Hence the reason if you really want to check your video you need an external monitor or else just learn to know what aren't real artifcats and what to freak out about.
TimmyRaa wrote on 11/12/2003, 7:43 AM
That's kinda what I suspected, except the *proper* 16:9 stuff looks perfect on my PC screen. As I'm watching the finished rendered movie, it's ONLY the cropped 4:3 shots that appear jagged.

I guess the only way to check, is to play it back on my telly!! :o)
farss wrote on 11/12/2003, 8:14 AM
Timmy,
check it on a real TV unless you can hook it upto your VV system.
If your camera can do passthrough then you can use that to go from your firewire port via the camera to the TVs Av/V inputs. I'm assuming it's easier to move the TV than PTT and hook camera upto TV.

I didn't really think through what you've done, it could be that stretching the lines vertically has caused some weird problem but I kind of doubt it.

BTW using most cameras in 16:9 does result in some loss of image quality, basically the camera is doing electronically what you're doing to your 4:3 footage so it causes a drop in resolution. The only way to avoid this is a camera with 16:9 CCDs or fitting a 16:9 anamorphic lens on the front of the camera. Niether of these is a cheap option.

Also mixing two types of cameras on a two camera shoot is not a good idea. Each camera has its own unique way of recording the image due to a host of factors so when you cut from one camera to another the difference is very noticeable. You can get around this to some extent with colour correction etc but good to avoid if you can.

Might I also ask how those without a 16:9 TV are going to view your footage?
Your video is going to look very squashed on a 4:3 TV. One trick around this is to use 14:9 letterboxed, looks OK on a 4:3 TV and still fills a lot of the screen at 16:9.

Let us all now how you go,
TimmyRaa wrote on 11/13/2003, 5:33 PM
>> Let us all now how you go

Well, I checked it on a CRT, and sure enough the lines were still there. After much post-production fiddling with TMPGEnc, and playing with (de)interlacing, I discovered that it could remove a lot of the lines with its 'Deinterlace' options. I went back into VV to see if this could help out - better to perform it sooner in the rendering process than later - and sure enough there's a 'Reduce Interlace Flicker' switch, that can be turned on for the individual problem clips.

I've rendered a part of it, and all's looking smoooooooth so far!!
farss wrote on 11/13/2003, 7:31 PM
Your pretty much at the limit of my knowledge on this.

Don't really know just what that plays with or its likely impact on total image quality. I think you really need to get some input from someone who really understands the internals of VV.

It is a truly amazing tool, I just wish there was some very specific info on what a lot of these switches actually do and when to use them and their total impact in various scenarios.

I think there is a White Paper on thi site about 24p, have you found it and read it?

I haven't and therefore don't even know if I'm sending you down a blind alley. It's just that I don't understand why that switch cured your problem as you shouldn't have any real interlacing to deal with as I understand it but then again...
TimmyRaa wrote on 11/14/2003, 3:22 AM
My only concern so far has in fact been picture quality - obviously if it's applying some filter to the picture, there may be some detail lost in whatever blending it does. Like you, I'm also not sure why I would have interlacing problems in the first place; maybe I'm not though, it's just that this particular filter blends out my jaggedness, in this particular instance. I must admit though, when I was playing with deinterlacing options in TMPGEnc - which I believe actually mathematically correct, not just blend interlacing problems - the results of an incorrectly interlaced image were strikingly similar to my problem.

As far as the image quality goes though, some slight loss of detail is *far* preferable to those horizontal lines!

Thanks for your help so far - I'll have a hunt around for that white paper.