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

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

13. Demo (Just Weird)
Skew
Aspect ratio
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. Some implementation detailsR W v0 u0 V L T f H
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 V L T f H q d
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.)
Draw horizontal bar at horizon line t
1-t p1 p2
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