I remember one project I worked on - it was a couple of shots for a friend’s short, and I had to put a picture onto a (then blank) cinema screen. There was someone standing on a stage in front of the screen who I had to roto out. Looking back on it, it was an amazingly rough job - mainly because I never really understood what these horizontal lines were when he moved. At the time, I ignored them, and roto’d somewhere between the two edges that I saw (I considered doing a zig-zag roto, but decided that that would be far too much work….)

If you’re sitting there thinking that I was a fool, you’re right (although, in my defense, this was 5 years ago, and I was only just starting this kind of thing at the time.) then carry on, and I’ll run through how to get Shake to realise that footage is interlaced.

If you’re wondering what on earth could have caused it, then please read this article (you don’t need to read the whole thing, just the bit near the top about interlacing - although there is some good stuff in the rest of the article).

So, if you’ve got some interlaced footage, how do you deal with this in Shake?

There are two parts to this. When you’re working in Shake, you only want to be looking at individual fields, but when you render, you want to be rendering out both fields for each image.

1) Working in Shake with fields
Two very simple steps here….

First of all, you need to tell your FileIn node(s) that the footage they are looking at is interlaced. You do this with the “deInterlacing” parameter. This has three options:

• off : Do not deinterlace



• odd : Deinterlace, with the odd-numbered lines coming first



• even : Deinterlace, with the even-numbered lines coming first

(If you’re wondering how to figure out whether you want odd or even, I’ll get to that in a second.)

Once you’ve set your footage to be deinterlaced, you’ll find that you now only see one of the fields. The second field for each frame is available, but at time.5 To work in increments of 0.5, change the “Inc” value in the bottom right of the Shake window.

Once you’ve done this, go through a few frames, a field at a time. If the motion looks right, then your deinterlacing option is right. However, if it looks like it moves forwards a load, and then back a bit, then forwards a load, then back a bit, then you need to change your deinterlacing mode.

When you’re comping interlaced footage, this is how you should be working - checking each 0.5 frames, and only viewing fields.

2) Rendering out both fields

If you were to set a render going with Shake set up as above, you’d find that your output images would only contain one of the fields, and you’d be losing a lot of information.

To get Shake to render out both fields, you need to go into the Globals, open up the renderControls and set fieldRendering to whichever mode you want (”off”, “odd” and “even” again). Once you’ve done this, you will find that you be seeing the footage interlaced again (hence why you don’t want to be working with it on), but all of your animation will still be on a field by field basis.

A good way to demonstrate this is with a quick RotoShape. Without any field modes turned on, create a RotoShape node, and give it some kind of animation. If you then set the fieldRendering to either “odd” or “even”, you’ll see your RotoShape is suddenly interlaced… This is because it’s actually showing (and rendering) your RotoShape at two times at once - the frame you’re on, and 0.5 frames later.

I hope this has been somewhat coherent - I was kinda digging for ideas for this week’s Shake tip - I’ll try and come up with something a little more interesting for next week…. (suggestions below, please)

This entry was posted on Monday, April 18th, 2005 at 20:28 and is filed under Shake Tips. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.