LAUSR

To the Editor — State-of-the-art 3D-rendering software for microscopy data (Imaris, Bitplane; Arivis 4D Viewer, Arivis AG; Volocity, PerkinElmer; FluoRender1) assembles animations based on key frames: the user stores different scene transformations in several key frames along a timeline, and the rendering engine creates a smooth animation by interpolating between them. The number of required key frames, however, increases considerably as animations become more complex: a full rotation around a single axis with constant speed requires at least three key frames, and substantially more are required for compound motions such as a combined rotation around multiple axes (Fig. 1a, Supplementary Video 1) or nonlinear motions, which are essential for achieving smooth and pleasant transitions. The definition of key frames by the user then becomes tedious and irreproducible. 3Dscript, an ImageJ/Fiji2,3 plugin, addresses the need for an intuitive way to assemble complex and high-quality animations. Here, animations are described by a list of instructions such as “From frame 0 to frame 180 rotate by 180 degrees horizontally ease-out” written in a syntax that is based on natural English language (Fig. 1b, Supplementary Notes). Each sentence starts with a frame interval that is followed by an action (e.g., “rotate,” “translate,” “zoom,” “change”) and the associated parameters. It ends optionally with an easing keyword (e.g., “linear,” “ease-in,” “ease-out,” “ease-in-out”) describing nonlinear motions often used in the animation of user interface elements in modern web design. 3Dscript provides instructions for spatially transforming an object in 3D; for animating 4D timelapse data (Supplementary Video 2); and for changing rendering properties such as contrast, channel weights, clipping and so on (Supplementary Videos 3 and 4). Unlike in key-frame-based animation, arbitrarily complex motions are intuitively implemented via the chaining of multiple instructions. Transformations, which are generally order dependent, are naturally applied in the order in which they appear in the text. Mixing of rotations and translations appropriately allows users, for example, to shift the center of rotation and generate planet-like motions, with an object rotating at the same time around both its own and an offset axis. Multiple instructions that apply in the same frame interval can be written concisely as enumerations (Fig. 1b). For the animation of motions that follow parametric paths such as Lissajous curves, user-defined ImageJ macros can replace any numeric parameter in 3Dscript, such as the number of degrees in a rotation (Supplementary Notes, Supplementary Videos 5 and 6). Macros are evaluated at runtime as functions of animation time. A dedicated editor based on Fiji’s script editor2 supports users in composing animations. During typing, written text is automatically completed (Supplementary