Frame by Frame VS. Tweening

When it comes to traditional 2d animation, as opposed to the 3d kind seen in most major hollywood animations these days, there are mainly two different kinds of animation. Frame by frame, and tweened. Let's look at each individually.

Frame by Frame animations

Frame Rate refers to the number of images that make up an animation over a given period of time. The acronym "FPS" would of course be "Frames per second".

Frame by frame animation is probably what most people think of when they think of hand drawn animation. In this style of animation every frame of an animation is drawn, by hand, to show fluid movement of objects and surfaces that can move and change over time.

The fluidity of the movement depends first and foremost of the frame rate.

Tweened animations

"Tweening" refers to a function within an animation program whereby the user defines "keyframes" that begin and end a section of animation and computer software automatically finds the average position, rotation, and scale of various points between those keyframes. Basically it's when the computer smooths out animations for you.

It's not the silver bullet the basic definition might have you believe however. Tweening can NOT create new frames of animation. If an object is to appear as if it is rotating the computer will not instantly know how to draw an object form that new point of view. Tweening can move objects, but the same side of that object must always face the camera.

If an object needs to rotate, then a new version of that object must be drawn.

This form of animation became popular for television shows, especially for children, where the limited number of drawn frames helps to keep the cost of an entire animation low.

Let's look at a few examples of what it looks like in motion. For each of the following clips keep an eye out for the following qualities...

  • How characters seem to be divided into "parts". Heads, hands, parts of the hair, are static images that move independent from one another.
  • How these individual parts move fairly smoothly as long as they are facing one direction.
  • How the characters don't rotate smoothly, or rotate to face another direction very quickly to minimize the number of frames that need to be drawn to show that rotation.

The above is a clip from "Foster's Home for Imaginary Friends" from 2009, the below is a clip from "Teen Titans Go!" from 2013.

Common interfaces

Thankfully there are a few functions and workflow concepts that are common amongst animation programs.

Onion Skinning

When animating, especially with a frame-by-frame approach, it can be difficult to know where you should draw / place an object on one frame without knowing where it was on the previous frame. To achieve smooth animation an object can not change either position or shape too much from the previous frame or else the animation will seem to "jump" or jitter around.

Many programs will include a feature called "Onion skinning" which alleviates this problem.

Onion Skinning is an option to display neighboring frames of an animation on a single frame so that the user can better position the drawing of the selected frame.

Typically the neighboring frames shown through onion skinning are made transparent so that you can only "kind of" see them. Some programs like Adobe Flash will also allow you to display the neighboring frames as outlines. You should also be looking for an option to change how many frames are included in the transparent image. This is important because the more neighboring frames that are displayed the harder it will be to read the image as a whole.