1 Another Look at Camera Control Karan Singh †, Cindy Grimm, Nisha Sudarsanan Media and Machines Lab Department of Computer Science and Engineering Washington University in St. Louis † University of Toronto

2 Cameras What is camera control? Manipulation of camera parameters Projection of 3D geometry into 2D plane Applications Interactively navigate around a scene (games) Create a fixed camera path (movies) Use different viewpoints to understand structure (visualization) Take pictures

3 Cameras Cameras as projection Computer graphics Physical camera From, at, up, field of view 11 dof total View matrix

4 Cameras Cameras in different fields (cont.) Artists have a qualitative vocabulary Describe relationship of camera to object in the scene Perspective effects One point Two point Three point Horizon line Vanishing point

5 Cameras Goals Visualization of camera parameters in the 2D image E.g., feed back on perspective distortion Manipulate current projection New position indicates desired projection change Changes appropriate camera parameters May change multiple parameters Minimal mouse, keyboard use Current approaches use entire right button Click-through interface

6 Cameras Related work Original camera paper J. C. Michener, I. B. Carlbom, Natural and efficient viewing parameters, SIGGRAPH 80 Trackball manipulation Michael Chen, S. Joy Mountford, and Abigail Sellen, A Study in Interactive 3D Rotation using 2D Input Devices, SIGGRAPH 88 Through-the-lens camera control Use image constraints to change camera parameters Not very stable Jim Blinn, Where am I? What am I Looking at?, IEEE CG&A, 1988 Michael Gleicher and Andrew Witkin, Through-the-lens camera control, SIGGRAPH 92

7 Cameras The IBar A cube centered along the look vector Changing the rendering of the cube changes the camera in a corresponding way Different segments move limbs simultaneously Cyan = top and bottom left limbs Red = left and right bottom limbs Rendering of cube reflects projection parameters

8 Cameras Demo (traditional) Dolly in and out Rotate left-right up-down spin Pan (object-centric) Zoom (object-centric) Pan (camera-centric) Zoom (camera-centric) Allows framing

9 Cameras Demo (Perspective change) Dolly + zoom Dolly in and out Center of projection (horizontal – vertical)

10 Cameras Demo (Just Weird) Aspect ratio Skew

11 Cameras Camera- versus object-centric Camera-centric Allows “framing” of objects Position cube in relation to scene Object-centric Traditional camera-moves-with-mouse Nice to have both Map different limbs E.g., zoom using the left handle is camera- centric, the right handle is object-centric

12 Cameras Changing parameters simultaneously Dolly plus zoom Calculate dolly in Find zoom that keeps everything at a distance d away the same size Center of projection Translate in reverse direction

13 Cameras In practice In use in short animated film, Ryan Used for dramatic perspective changes

14 Cameras Summary Visualization of COP, horizon line, perspective distortion Also at arbitrary points in the scene One mouse button for all 11 parameters Shift key chooses less-common action Click through interface Toggle key for disabling Usable perspective manipulation Simultaneous editing of parameters

15 Cameras Drawbacks Remembering which parameters go where Visual clutter User study comparing IBar to Maya camera Primary conclusion: camera manipulation is hard for both naïve and knowledgeable users Unable to manipulate camera to match a target scene IBar helped people to “learn” camera manipulation

16 Cameras Future work Reducing number of parameters on widget Multiple widgets, quick swap between them Similar handles Pre-viewing of manipulation effects What does this handle do? Bookmarking and camera paths Visualizing in scene May be out of scene