Stop motion in Blender: the frame-by-frame effect, in 3D and with photos

Stop motion, or frame-by-frame animation, means photographing an object or a figure, moving it slightly, then taking another photo, and so on. When the film is played, the successive poses give the illusion of movement, with the slightly jerky look that is part of its charm: clay animation, brickfilms made of bricks, cut-out paper animation. In 3D, you reproduce this look by stopping Blender from smoothing the movement between two keyframes. This guide shows the two methods, the Grease Pencil variant, and how to edit a real photo stop motion.

The principle: hold each pose

By default, Blender calculates in-between positions between two keyframes: the movement is smooth, frame after frame. Stop motion does the opposite: each pose stays frozen for several frames, then jumps to the next one. The rhythm is described as "ones", "twos" or "threes":

Method 1: Constant interpolation

This is the simplest method if you set a keyframe yourself for each new pose. Select the keyframes in the Timeline, the Dope Sheet or the Graph Editor, press T and choose Constant. Each value then stays the same until the next keyframe, then changes all at once. Setting a keyframe every two frames is enough to animate on twos. The guide to animation in Blender covers setting keyframes and the Graph Editor in detail.

Method 2: the Stepped Interpolation modifier

If the animation already exists and is smooth, there is no need to redo it: the Stepped Interpolation curve modifier cuts it into steps. In the Graph Editor, select a curve, open the sidebar (N), go to the Modifiers tab, then Add Modifier, Stepped Interpolation. Its settings:

• Step Size: the number of frames for which each pose is held. 2 to animate on twos, 3 to animate on threes.
• Offset: shifts the moments when the pose changes, useful so that two characters do not change pose at the same time.
• Start Frame and End Frame: limit the effect to part of the animation, for example to keep one passage smooth.

The advantage: the original curve stays intact. Disable the modifier to get the smooth movement back. It is added curve by curve; for a rigged character, select the curves of all the bones before adding the modifier from the Channel menu, Add F-Curve Modifier.

In drawing: Grease Pencil and Time Offset

With Grease Pencil, the animation is already frame by frame: each drawing is a keyframe. The Time Offset modifier then plays with these drawings: it shifts their start (Frame Offset) so that several copies of the same character do not move at the same time, plays them backwards (Reverse) or back and forth (Ping Pong), and the Fixed Frame mode shows a chosen drawing, for example one mouth shape among several prepared ones.

Cut-out paper animation

Cut-out animation animates flat pieces (arms, legs, head) laid on top of one another. In Blender, each piece becomes a textured plane:

1. Prepare each piece as a PNG image with a transparent background.
2. In the 3D Viewport, add it with Add, Image, Mesh Plane: Blender creates a plane with the proportions of the image, with a material that displays it.
3. Place the origin of each piece on its joint (the shoulder for an arm), then link the pieces together by parenting so that an arm follows the torso.
4. Offset the pieces slightly in depth to control what passes in front, and film with an orthographic camera (entry in French) to keep the flat look.
5. Animate the rotations with Constant interpolation or the Stepped Interpolation modifier, as above.

Making the effect convincing

A real stop motion is never perfect, and that is what makes it recognisable:

• Slight errors in position: an object that "breathes" by a few millimetres from one pose to the next, like a figure adjusted by hand.
• Tactile materials: modelling clay with fingerprints, the shiny plastic of bricks, paper with a visible grain. The guide to textures in Blender shows how to get them.
• A miniature camera: a shallow depth of field gives the impression of a small set filmed up close; the depth of field entry (in French) explains the setting.
• No motion blur: every photo in a stop motion is sharp. Leave motion blur turned off.

Editing a real photo stop motion in Blender

1. Photograph each pose, with the camera fixed in place and constant lighting, and number the files in order.
2. In the Video Editing workspace, add the photos as an image sequence (Add menu, Image/Sequence, selecting all the photos).
3. In the Output Properties, set the Frame Rate, for example 12 frames per second, and adjust the frame range to the length of the sequence.
4. Choose a video format and render the animation, as explained in the guide to rendering an animation in Blender.

Rendering half as many frames

An animation held on twos repeats each frame twice: there is no point in rendering it twice. In the Output Properties, set the step of the frame range (Frame Range, Step) to 2: Blender renders only every other frame. Render them as image files (PNG, for example), then assemble them into a video at 12 frames per second instead of 24 in the Video Sequencer, as for a photo stop motion: the rhythm is identical. On a long animation in Cycles, that is half the render time; the render time calculator gives the order of magnitude.