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Another Look at Camera Control

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. What is camera control?. Manipulation of camera parameters

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Another Look at Camera Control

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  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. 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 Cameras

  3. Cameras in different fields • Computer graphics • From, at, up, field of view • View matrix Cameras

  4. Cameras in different fields (cont.) • Film, photography • Camera is physical object • Describe movement of camera itself • Dolly in/out, tilt, pan, roll • Zoom in/out • Graphics systems use same vocabulary • Through-the-lens • Exterior views • Camera-centric • Reposition the camera • Object-centric • Reposition the camera relative to an object Cameras

  5. Cameras in different fields (cont.) • Mathematics • 4X4 matrix • 11 degrees of freedom • Straight lines to straight lines • Computer vision • 3X4 matrix • Don’t keep depth • Graphics maps 11 dof to “useful” parameters • J. C. Michener, I. B. Carlbom, Natural and efficient viewing parameters, SIGGRAPH 80 • Six extrinsic parameters (position, orientation) • 5 intrinsic parameters (center-of-projection, focal length, skew, aspect ratio) Cameras

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

  7. 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 Cameras

  8. 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 • K. Henriksen, J. Sporring, and K. Hornbaek • Virtual trackballs revisited, IEEE TVCG Cameras

  9. Related work • 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 Cameras

  10. 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 Cameras

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

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

  13. Skew Aspect ratio Demo (Just Weird) Cameras

  14. 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 Cameras

  15. V W V H f v0 d f T L u0 H q R T L Some implementation details • Camera parameters • T – Eye position • L – Look vector • V – Up vector • W,H – width, height • f – focal length • u0,v0 – center of projection • d – distance to object Cameras

  16. Drawing the IBar • Cube edge is centered on look vector • Adjust for center of projection • Size of cube adjusted so is always sc high on screen Cameras

  17. Drawing the IBar (cont.) t p1 p2 1-t Draw horizontal bar at horizon line Cameras

  18. Drawing the IBar (cont.) • Feedback • IBar highlights when mouse is over active part • Indicate selected segment with circle Cameras

  19. Manipulating the IBar • Relative, not absolute • Determine which limb, and which segment selected • Determine ratio/percentage moved • Change corresponding parameter(s) by ratio • E.g., • Multiply zoom by ratio of length change • Pan by mouse movement Cameras

  20. Manipulating the IBar • Limb movement constrained to vertical (or horizontal) • Shift key unconstrains • Left-right movement rotates up or down • Up-down movement changes center of projection • Pan unconstrained • Shift key constrains • Stem • Shift chooses aspect ratio or skew Cameras

  21. 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 Cameras

  22. Camera- versus object-centric • Camera-centric • Render cube with new camera, scene with original camera • Object-centric • Render both cube and scene with new camera • Changing parameters • Invert operation (i.e., pan in the opposite direction) Cameras

  23. Centering the IBar on an object • Allows rotation around arbitrary point • User selects point p in scene • Determines d • Render at p • Rotation • Translate p to origin (and camera) • Rotate • Translate back Cameras

  24. In practice • In use in short animated film, Ryan • Used for dramatic perspective changes Cameras

  25. 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 Cameras

  26. 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 Cameras

  27. 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 Cameras

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