Compositing question

[Mongo_Slade]

So i was watching spongebob today and i noticed in his pineapple house he is usually sitting on his recliner seat which is a flat object/drawing ,my question is is the chair two layers because when he sits down he is plush into the seat or well how is this technique done meaning having a 2d character interact with and object such as a chair under a table ,inside of a car sticking a head out etc. i hope i made this question clear enough lol

[jeremyhopkins]

Yes, if Spongebob is sitting in a chair there's an underlay of the chair that is behind him and part that is overlay over top of his body. If Spongebob's arm is on top of the armrest on the chair, that would be another overlay on the chair. As an example the layers would be:

Spongebob arm
Front chair
Spongebob
Back chair
Background

[Mongo_Slade]

so basically when a scene is like this the object is basically a layered obect then right?,so how did they do this in the eraly days of animation such as tom and jerry etc.?

[jeremyhopkins]

It would be the same. The only difference is that Tom and Jerry was done on cels and filmed with a camera and Spongebob is composited with a computer.

[GdeSouza]

It needn't be that complicated. The bg element is one layer, the character one layer. The animator would just not draw the part of Spongebob that goes behind the front arm of the chair. A match line , A line matching the contour of the element of which Spongebob is behind is on his layer so they know where to paint to. In the old days this was indicated in blue on the drawing. It wouldn't photograph so the cel painters would have the drawing beneath the cel to know where to paint to.
I don't know how they do it digitally whether scanned or paperless but imagine the animator could do the match line in balck then remove it digitally after The character drawing is filled with paint.

In the days of Tom & Jerry they had to be real careful as to how many levels as things would darken the more cels were overlayed. That's why in old cartoons you see a color difference on a held character and his animated arm for example. They didn't paint his arm a different color, it was the difference caused by levels of cels.

[jeremyhopkins]

Yes, that makes more sense especially for cel.

[jeremyfries]

By the way, when you look at drawings from old cartoons, sometimes you see "REG" written on them. This is what it meant: the drawing was to be "registered" to some background element such as a chair or doorway, just like described above.

Don recently described this in one of the webchats, and I suddenly thought, "So THAT'S what that meant!" :)