How does tweening work?

Tweening is a computer-assisted animation technique. It consists in moving or morphing a digital element between 2 keyframes. This by using an animation software.

In 2D animation, the animator will specify 2 key states. So, he will be able to change the scale, location, color, etc. values of an object. Then let the computer calculate the transition between the 2 keyframes.

The most basic example of this, is a circle that moves horizontally from left to the right :

Animation par interpolation basique d’un cercle
Basical inbetween animation of a circle

Of course, tweening animation isn’t only used for moving objects.

So we can modify all the values of the object between 2 different states (keyframes). The goal is to play with its color, size, form or even transparency to create auto-generated transitions (or morphing). All of this between 2 poses, in an automatized way, without having to redraw each inbetweens :

Animation d’un morphing entre 2 formes différentes
Morphing animation between 2 different shapes

Because it is computer-assisted animated, tweening is also used in 3D. It is used to make the transition between 2 numeric values configured by keyframes.

The result remains the same, and the possibilities are higher in 3D, but also way more complex :

Sphère 3D pour laquelle on a animé la texture pour faire varier le relief et la luminosité
3D sphere with animated texture to add bump and luminosity variety

Tweening animation begginings

Computer-calculated animation began in the 1940s. When pioneers began to experiment computer-generated virtual images.

One of the fathers of the genre, John Whitney, created the opening credits of Alfred Hitchcock’s “Vertigo” (1958) in collaboration with the graphic designer Saul Bass :

In the early 1960s, Bell Labs, a research center interested in computer experimentation and its various future applications, began to create fully computer-generated visual content.

Edward Zajac, a researcher at Bell Labs and considered one of the first digital artists ever, produced one of the first fully computer-generated films.

This film is named “A Two Gyro Gravity Gradient” (1963). It was created to demonstrate how a satellite can remain aligned face to Earth during the course of its orbit around it :

Flash animation software (Animate CC) and tweening movement

Adobe Flash (originally Macromedia Flash for regular users) is an animation software. Using vector, bitmap or script generated images (with ActionScript) it is used to create multimedia content. Content destined to be published on the Web.

It can be used to create animations for video games or mobile apps. But its use was mainly devious by animation studios for 2D TV series or animation film productions.

It is nowadays a standard and one of the most used softwares in the animation industry.

It also allows, with the use of its drawing tools, to produce traditional animations.

Cheap and easy to use, it also permit cut-out characters animation.

It is used to optimize the speed of production, while reducing costs while keeping a good visual quality. That’s why studios love it.

That said, for the “purists” of traditional animation, Flash was one of the reaons why traditional animation vanished. Precisely because of all its advantages and by wanting to save too much on the production, as a result, jerky animation pollutes the market.

Jerky animation, sloppy and degraded visual quality, old 2D animators of the golden age of traditional animation can have difficulties adapting to this kind of computer-assisted animation…

Fortunately, there are other alternatives on the market, such as Toonboom’s Harmony software.

This software has the particularity, in addition to having all the same features as Flash for cut-out animation, to give back its nobility to traditional animation.

It allows, thanks to its advanced drawing tools and its light table, to recreate a more traditional approach and feeling to 2D animation by computer and this is most appreciated by those who are nostalgic of good old pencil on paper animation!

Tweening animation in 3D

In 3D animation, we use the same principle as computer-assisted 2D animation, so we generate interpolations between 2 key poses (or keyframes in 3D).

Each time a new keyframe is created, a set of numeric values is saved and it determines the state of a 3D object in a virtual space at a given time.

For example, we can animate a sphere that moves from point A to point B horizontally, by changing the translation values of the object on the z axis.

The same goes for animating the 3D object in rotation, scale or any numeric animable values. We also can animate the texture, the light, or the skeleton of a character’s rig by changing the weight value applied to the character, depending on the result we want. The possibilities are limitless!

As with any interpolation animation software, you will usually animate using a motion editor (Graph Editor in 3D).

In this motion editor, we can play with curves in order to apply “ease in / ease out” or animate any property of the object in a visual way rather than typing numerical values :

Graph Editor dans le logiciel 3D Maya
Graph Editor in 3D Maya software

Fenêtre de l’Éditeur de mouvement dans le logiciel Flash
Motion editor in Flash animation software

Le graph editor dans le logiciel de compositing Adobe After Effects
Graph Editor in Adobe After Effects compositing software

Of course, who says digital animation, says animating with numerical values.

Which is, for an artist, the opposite of the creative and traditional process that he expected when he spent all his time sketching in school instead of studying …

But we have to adapt to contemporary time, as animation softwares evolve and offer more interesting options, it can be fun to do computer animation espacially if we are able to apply the traditional animation techniques in the digital style!


I am a professional 2D and 3D animator who worked for years on Animated TV Series and Video Games. (see complete profil description on the sidebar of the Blog). Have fun!

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