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I was watching an episode of _Shirobako_. I love how the anime gives you a
slightly in-depth view of the production process. However, something I can't
get my mind around is those few segments that involve CGI (in anime in
general) with the interaction of traditional 2D animation such as stationary
or moving objects.

In the episode, a scene in _Exodus_ where the girls ride a jeep while avoiding
an explosion was shown in key animations/"genga":
<https://sakugabooru.com/post/show/10903>.

As you can see, the 3D bike and characters basically move together on a plane.
Could it be that the bike is animated frame by frame in traditional animation
somehow? Or the other way around? Or could it be more technical than those?


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2015-01-27T20:46:06.563
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2023-09-10T03:02:10.077
2023-09-10T03:02:10.077
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anime-production
How do 3D objects coincide with traditional 2D animation?


The bike can be animated in a 3D model editor application and overlayed upon
the ready 2D frames. It doesn't really matter which application both come
from, since they can all export frames to static images. 3D editors have
motion direction, of course, or else we would not see much 3D movies. And you
can not add anything else aside from the main 3D mesh with applied texture, so
that the background will be transparent upon frame export. You know how they
have those "layers" in Photoshop? Well, that is it. One of them comes from 2D
app, the other from 3D. Nothing special.

Images taken [from this Autodesk 3ds Max™
tutorial](http://forums.cgarchitect.com/34787-help-rendering-vray-reflection-
transparency.html) showing how not much of a rocket science it is to create 3D
scenes with transparency (click images for full resolution):

[![](https://i.stack.imgur.com/D6FG5l.jpg)](https://i.stack.imgur.com/D6FG5.jpg)

The image with transparent background and white shadow with gradual
transparency changing, after exporting from a 3D editor, can be imported into
a 2D editor (such as Adobe Photoshop) and be laid over some colored rectangles
like this:

[![](https://i.stack.imgur.com/6hsccm.jpg)](https://i.stack.imgur.com/6hscc.jpg)
[![](https://i.stack.imgur.com/gPazqm.jpg)](https://i.stack.imgur.com/gPazq.jpg)

We also have sites like
[GraphicDesign](https://graphicdesign.stackexchange.com/) on [StackExchange
Questions and Answers sites network](http://stackexchange.com/sites) that [ask
questions on similar
topics](https://graphicdesign.stackexchange.com/questions/27507/how-can-i-
create-and-batch-this-3d-planes-effect) with such illustrations:

![](https://i.stack.imgur.com/nLvit.png)

You say "traditional animation", but that really means collaging paper
elements on a table, taking a shot of the scene and later on gluing together
the resulting frames into a cinema roll. You must want to know about the
modern day way, so that is what I described above.

Older animation techniques require the use of celluloid sheets, which are
transparent sheets of plastic, to make the things simple. Are you familiar
with the term _cel-shading_? Well, this is where the modern day 3D animation
technique comes from − the older days method of drawing the outline of objects
on a cel sheet. It goes something like this: You draw the black outline and
the fill inside areas with colored paint. Then you place it above the scene
image and move around or swap for other cels with different character poses.

[![](https://i.stack.imgur.com/rXMAYm.jpg)](https://i.stack.imgur.com/rXMAY.jpg)
[![](https://i.stack.imgur.com/GhRpdm.jpg)](https://i.stack.imgur.com/GhRpd.jpg)

There are a number of techniques used to overlay 3D objects onto ready frames
of anything else, used by all sorts of "magicians" in their shows. You could
ask google how they did it before computers and find out something new.


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2015-01-28T20:46:47.583
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answer


# **Construction of Anime Frames**

When a frame of anime is made, there are different layers to the images. These
allow for easy editing of a particular component.

Here's an example image (taken from Wikipedia) .

![enter image description here](https://i.stack.imgur.com/DgIoAs.jpg)

Presume that we are releasing an anime about this bird and this is the image
that comes up in the title screen. We are ready to release the first episode,
but the director says _" actually, that bird is too far to the left, we need
to change it."_.

If our image didn't have layers, when we move the bird we won't know what was
behind it originally, leaving a hole in the image:

![enter image description here](https://i.stack.imgur.com/Ig24us.png)

Because we're a very experienced set of animators however, we know that we
should use layers. We have one layer with the background on it, and another
layer that is transparent apart from the image of the bird. Moving the bird
layer should be much less painful now.

![enter image description here](https://i.stack.imgur.com/eqFy4s.png)

![enter image description here](https://i.stack.imgur.com/D7e7ys.jpg)

It is by using layers in images, that animators can put in other mediums such
as 3d, or real-life photos with ease.

# **How 3D can be put onto 2D?**

Here's an example 3D model that I found of a motorbike within a 3D editor:

![enter image description here](https://i.stack.imgur.com/JjTti.png)

In the editor, you can control the camera (left) and the lighting(right) [both
highlighted in orange] of the scene. This particular scene only has one light
source, but you could have several. ![enter image description
here](https://i.stack.imgur.com/frReM.png)

Editors usually allow the user to render a 2D image of what the camera can
see. By moving the camera around, you could get all the images you need for
the frames. You can then insert them on their own layer of the 2D images.

![enter image description here](https://i.stack.imgur.com/7k3Ghm.png) ![enter
image description here](https://i.stack.imgur.com/ZyEjum.png)

There are some problems with this approach though, A better way of getting the
result though. If there are multiple movements in the system it is hard to do
keep track of their timing from frame to frame. Also, if other camera angles
are requested by the director, the process must being again. For this reason,
making scripted movements is a much better approach. The frame-by-frame
solution would work well for objects such as parked cars, or objects with
little movement.

Manual setting of movements (examples: rotate wheel of bike 5rps, 'turn
30degrees left after 4 seconds) and [**Key
Framing**](http://www.arch.virginia.edu/arch545/handouts/keyframing.html) is
how an animator sets up this system.

![enter image description here](https://i.stack.imgur.com/LwSuk.png)

3D animators can then export the animation as several images, as seen from the
camera's point of view. They can then be added to the layers of the 2D frames.

And if the director wants to change an angle, all the 3D animators have to do
is move the camera and regenerate the images.

* * *

I'm not 100% certain about this but I imagine that the moving 2D parts of a
frame are done after the 3D rendering as 3D's precise movements would make it
hard to adjust for the 2D's less refined movements, wheras 2D is easily
changeable to accomidate the 3D models - it also allows the camera angles to
be changed early on.


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